2019 Drainage Design Manual

DRAINAGE DESIGN MANUAL CITY OF DALLAS SEPTEMBER 2019

City of Dallas DRAINAGE DESIGN MANUAL

SEPTEMBER 2019

SECTION 3 Contents ROADWAY DRAINAGE DESIGN ��21 3.1 GENERAL �� 22 SECTION 1 3.2 IMPROVED ROADWAY DRAINAGE �� 22 INTRODUCTION ��1 3.2.1 Street Capacity 22 1.1 PURPOSE ��2 3.2.2 Straight Crown Street 23 1.2 SCOPE ��2 3.2.3 Parabolic Crown Street 23 1.3 OVERVIEW ��3 3.2.4 Valley Gutter Flow 23 1.4 INTEGRATING DRAINAGE ��4 3.2.5 Flow in Alleys 24 1.4.1 Drainage Design Process 4 3.3 INLET DESIGN �� 24 1.4.2 Drainage Design Considerations 4 3.3.1 Types of Inlets 24 1.4.3 Defining a Project 5 3.3.1.1 Grate Inlet 25 1.4.4 Sustainable Design Guidelines 5 3.3.1.2 Curb Inlet 25 1.4.5 Pre-Development Meeting 5 3.3.1.3 Y-Inlet 25 1.4.6 Design Software 5 3.3.1.4 Combination Inlet 25 SECTION 2 3.3.1.5 Slotted Drain Inlet 26 HYDROLOGY ��7 3.3.2 Inlet Design Requirements 26 2.1 GENERAL �� 8 3.3.3 Inlet Capacity Calculations 27 2.2 HYDROLOGY �� 9 3.3.3.1 Grate Inlet 27 2.2.1 Rational Formula 9 3.3.3.2 Curb Inlet 29 2.2.1.1 Runoff “C” Value 9 3.3.3.3 Y-Inlet 30 2.2.1.2 Rainfall Intensity (i) 10 3.3.3.4 Combination Inlet 31 2.2.1.3 Time of Concentration (T ) 10 c 3.3.3.5 Slotted Drain Inlet 31 2.2.2 Hydrograph Methods 12 3.4 UNIMPROVED ROADWAY DRAINAGE �� 31 2.2.2.1 SCS Unit Hydrograph Method 12 3.4.1 Bar Ditch Design 31 2.2.2.2 Use of Other Hydrograph Methods 14 3.4.2 Bioswales / Bioretention Swales 31 2.2.2.3 Flood Routing 15 3.4.2.1 Bioswales 31 2.2.2.4 Hydrograph Time Interval Determination 15 3.4.2.2 Bioretention Swales 32 2.2.2.5 Gage Data and Calibration Methods 16 3.4.3 Culvert Crossing 32 2.2.2.6 Storage Options 16 3.5 ADDITIONAL ROADWAY 2.3 DETENTION / RETENTION ANALYSIS �� 16 DRAINAGE CONSIDERATIONS �� 33 2.3.1 Design Objectives 16 3.5.1 Utility and Drainage Infrastructure Requirements 33 2.3.2 Downstream Analysis 17 3.5.2 Alternative Pavements 34 2.3.3 Design Methodology 17 3.5.2.1 General Design Considerations 34 2.3.3.1 Modified Rational Method 17 3.5.2.2 Permeable Paving 34 2.3.3.2 Adjustment for Sustainable Drainage Measures 18 3.5.2.3 Permeable Unit Pavement System 35 2.3.4 Water Rights 19 3.5.2.4 Porous Pavers 36 3.5.3 Sand and Organic Media Filters 37

Dallas Drainage Design Manual i 3.6 ENCLOSED STORM DRAIN SYSTEM DESIGN �� 39 SECTION 4 3.6.1 Starting Hydraulic Gradeline Elevation 39 BRIDGE HYDRAULIC DESIGN ��65 3.6.2 Storm Drain Line Design 40 4.1 GENERAL �� 66 3.6.3 Lateral Design 41 4.2 DESIGN FREQUENCY AND FREEBOARD �� 66 3.6.4 Head Losses 41 4.2.1 Design Frequency 66 3.6.5 Manhole Placement and Design 42 4.2.2 Freeboard / Minimum Clearance 67 3.6.6 Tree Box Filters 42 4.3 FLOW REGIMES �� 67 3.7 CULVERT HYDRAULIC DESIGN �� 44 4.3.1 Low Flow Considerations 67 3.7.1 General 44 4.3.2 High Flow Considerations 68 3.7.2 Design Frequency 44 4.3.3 Supercritical Flow 68 3.7.3 Hydraulic Controls 44 4.3.4 Erosive Velocities 68 3.7.3.1 Inlet Control 44 4.4 CHANNEL CONSTRICTION �� 68 3.7.3.2 Outlet Control 44 4.5 SCOUR �� 69 3.7.4 Energy Gradient Analyses 45 4.6 BRIDGE DECK DRAINAGE �� 69 3.7.4.1 Energy Loss Through Culvert 45 4.7 ROADWAY OVERTOPPING �� 70 3.7.4.2 Energy Balance at Inlet 49 4.8 OTHER DESIGN CONSIDERATIONS �� 70 3.7.4.3 Determination of Outlet Velocity 50 SECTION 5 3.7.4.4 Depth Estimation Approaches 50 OPEN CHANNEL DESIGN ��73 3.7.4.5 Direct Step Backwater Method 50 5.1 GENERAL �� 74 3.7.4.6 Roadway Overtopping 50 5.2 OPEN CHANNEL HYDRAULICS �� 74 3.7.4.7 Performance Curves 51 5.2.1 Flow Classification 74 3.7.4.8 Exit Loss Considerations 51 5.2.1.1 Types of Flow in Open Channels 74 3.7.5 Flow Regime Determination 51 5.2.1.2 Subcritical Flow 75 3.7.5.1 Subcritical Flow and Steep Slope 51 5.2.1.3 Supercritical Flow 75 3.7.5.2 Supercritical Flow and Steep Slope 52 5.2.1.4 Critical Flow 75 3.7.5.3 Hydraulic Jump in Culverts 52 5.2.1.5 Hydraulic Jump 76 3.7.5.4 Sequent Depth 52 5.2.1.6 Uniform Flow 76 3.7.6 Other Culvert Design Considerations 52 5.3 DESIGN GUIDELINES �� 78 3.8 OUTFALL DESIGN �� 54 5.3.1 Manning’s ‘n’ Values 78 3.8.1 General 54 5.3.2 Design Frequency and Freeboard 78 3.8.2 Headwalls / Pipe End Treatment 55 5.3.3 Channel Velocity 78 3.8.3 Energy Dissipators 55 5.3.4 Channelization 78 3.8.3.1 Riprap Aprons / Basins 55 5.3.5 Channel Geometry 78 3.8.3.2 Concrete Aprons / Basins 61 5.3.6 Channel Slope 79 3.8.3.3 Baffle Blocks 61 5.3.7 Bed Controls 79 3.8.3.4 Baffled Outlets 61 5.3.7.1 Channel Drops 79 3.8.3.5 Drop Structures 63 5.3.7.2 Baffle Chutes 79 3.8.3.6 Other Energy Dissipators 63 5.3.7.3 Checkdams 80 3.8.4 Sedimentation Basin 63

ii Table of Contents 5.3.8 Channel Bends 80 SECTION 8 5.3.9 Channel Junctions 81 FLOODPLAIN AND SUMP 5.3.10 Bottom Width Transition 81 DESIGN REQUIREMENTS ��109 5.3.11 Superelevation 81 8.1 GENERAL �� 110 SECTION 6 8.2 FLOODPLAIN HYDRAULIC ANALYSIS �� 110 DRAINAGE STORAGE DESIGN ��83 8.2.1 Hydraulic Modeling 111 6.1 GENERAL �� 84 8.2.1.1 1D Steady Flow Modeling 111 6.2 DETENTION BASIN �� 85 8.2.1.2 1D Unsteady Flow Modeling 111 6.2.1 Design Guidance 85 8.2.1.3 2D Unsteady Flow Modeling 111 6.2.2 Low Flow Channels / Pilot Channels 86 8.3 REGULATORY FLOODPLAIN MAPS �� 112 6.3 RETENTION BASIN �� 87 8.4 FLOODPLAIN APPROVAL PROCESS �� 112 6.4 UNDERGROUND DETENTION �� 87 8.4.1 Fill Permits 112 6.5 STORMWATER PONDS �� 88 8.4.2 Sump Fill Permits 113 6.6 CONSTRUCTED WETLANDS �� 89 8.4.3 Floodplain Alteration Permits 113 6.7 RAINWATER HARVESTING �� 91 8.4.4 Other City Permits 113 6.8 RAIN GARDENS �� 92 8.5 ENHANCEMENTS AND RECREATIONAL USES �� 113 6.9 BIORETENTION �� 94 8.6 FEMA COORDINATION �� 114 6.10 INFILTRATION REQUIREMENTS AND TESTING �� 95 8.7 SUMP AND LEVEE AREAS �� 114 6.11 STORMWATER PUMP STATION DESIGN �� 96 8.7.1 Sumps 114 6.11.1 Design Guidance 96 8.7.2 Levee Setback 114 6.11.1.1 Pump Station Hydrology 96 SECTION 9 6.11.1.2 Pump Station Hydraulics 97 OTHER REGULATORY REQUIREMENTS ��117 6.11.1.3 Operation and Maintenance 97 9.1 GENERAL �� 118 SECTION 7 9.2 ENVIRONMENTAL AND CONSTRUCTION PERMITTING REQUIREMENTS �� 118 EROSION AND SEDIMENT CONTROL MEASURES ��99 9.2.1 Water Quality 118 Tree Mitigation 118 7.1 GENERAL �� 100 9.2.2 Section 404 Permitting 119 7.2 NATURAL CHANNEL SETBACK �� 100 9.2.3 Section 408 Permitting 119 7.3 TEMPORARY CONSTRUCTION 9.2.4 EROSION CONTROL �� 102 9.2.5 Aquatic Relocation 119 7.4 PERMANENT EROSION CONTROL DESIGN �� 102 9.2.6 Construction Permit Requirements 119 7.4.1 Grass / Vegetation 102 9.2.6.1 TPDES Construction General Permits 119 7.4.2 Turf Reinforcement 102 9.2.6.2 City Grading and Fill Permits 119 7.4.3 Bioengineering 102 9.2.6.3 Floodway Access Permits 119 7.4.4 Stone Riprap Design 104 9.3 EASEMENTS �� 120 7.4.5 Gabions 105 9.3.1 Storm Sewer Line Easements 120 7.4.6 Concrete 105 9.3.2 Detention / Retention Area Easements 120 7.4.7 Concrete Block Mats 105 9.3.3 Access Easements 120 7.4.8 Retaining Walls in Waterways 105 9.3.4 Slope Easements 120

Dallas Drainage Design Manual iii 9.3.5 Subsurface Easements SECTION 11 (Tunnels / Tieback Anchors) 121 OPERATION AND MAINTENANCE ��137 9.3.6 Utility Considerations 121 11.1 OPERATION AND MAINTENANCE 9.4 COORDINATION WITH OTHER AGENCIES �� 121 CONSIDERATIONS �� 138 9.4.1 County Requirements 121 11.2 OPERATION AND MAINTENANCE PLANS �� 138 9.4.2 NCTCOG 121 APPENDICES ��141 9.4.3 TCEQ 122 A.1 GENERAL �� 142 9.4.4 TxDOT 122 A.1.1 Applicable Regulations 142 9.4.5 USACE 122 A.1.2 List of Acronyms and Abbreviations 143 9.4.6 Texas Parks & Wildlife 122 A.1.3 Glossary of Terms and Definitions 143 9.4.7 FEMA 122 A.1.4 Sources 146 9.4.8 DART and Other Rail Systems 122 A.2 HYDROLOGY �� 147 9.4.9 Neighboring Cities 123 A.2.1 C Adjustment Factor Example 147 SECTION 10 A.3 HYDRAULICS �� 148 SUBMITTAL REQUIREMENTS ��125 A.3.1 Sag Inlet Design Worksheet 149 10.1 GENERAL �� 126 A.3.2 Manning’s n for Channels 150 10.2 PLATTING / DEDICATION OF A.3.3 Manning’s n for Closed Conduits WATER COURSES AND BASINS �� 126 Flowing Partly Full 153 10.3 DOCUMENTATION REQUIREMENTS �� 127 A.3.4 Gutter Flow / Inlet Computations 155 10.3.1 Drainage Reports 127 A.3.5 Full Flow Coefficient Values 156 10.3.2 Survey 128 A.3.5.1 Elliptical Concrete Pipe 156 10.3.2.1 Outfall Ditches Less Than 3ft Wide 128 A.3.5.2 Concrete Arch Pipe 157 10.3.2.2 Outfall Ditches More Than 3ft Wide 129 A.3.5.3 Precast Concrete Box Section 158 10.3.2.3 Culverts 130 A.3.5.4 Circular Concrete Pipe 159 10.3.2.4 Drainage Pipes 130 A.3.6 Energy Equations in Open Channels 160 10.3.2.5 Minor Headwalls and Wingwalls 130 A.3.6.1 Energy 160 10.3.2.6 Inlet Structures 131 A.3.6.2 Specific Energy 160 10.3.2.7 Floodplain Surveys 131 A.3.6.3 Froude Number 160 10.4 CONSTRUCTION PLAN PREPARATION �� 131 A.4 PROCEDURES �� 161 10.4.1 General 131 A.5 SUBMITTAL REQUIREMENTS AND FORMS �� 161 10.4.2 Conceptual Design Phase 131 A.5.1 Checklist for Storm Drainage Plans 161 10.4.2.1 Checklist for Conceptual Design Phase 132 A.5.2 Non-Standard Material Agreement Template 164 10.4.3 Preliminary Design Phase 132 A.6 OTHER �� 167 10.4.4 Pre-Final Design Phase 132 A.6.1 Materials Matrix 168 10.4.5 Final Design Phase 132 A.6.2 Media 172 10.4.6 Drafting Requirements 133 A.6.3 Seed Mixes 172 10.4.7 Plan Requirements 133 A.6.4 Recommended Plants 180 10.4.7.1 Drainage Area Map 133 A.6.5 Operation and Maintenance Plan 185 10.4.7.2 Plan / Profile Sheets 133 A.6.6 Annual Maintenance Schedule 186 10.4.7.3 Special Details 135 A.6.7 Maintenance Records 186

iv Table of Contents A.7 FIGURES �� 186 A.7.1 Capacity of Triangular Gutters 187 A.7.2 Parabolic Crown Street Flow Capacity 188 A.7.3 Alley Conveyance Without Curb 190 A.7.4 Alley Conveyance With Curb 191 A.7.5 Curves for Determining the Critical Depth in Open Channels 192 A.7.6 Section 2 Figures 193 A.7.7 Section 3 Figures 195 A.7.8 Section 5 Figures 205

Dallas Drainage Design Manual v Tables Figures Table 2.1 Probability of Exceedance Figure 1.1 Drainage Design Process Table 2.2 Design Storms for Drainage Elements Figure 2.1 Shallow Concentrated Flow Average Velocity Table 2.3 Runoff Coefficients for Zoned Areas Figure 2.2 Areal Reduction Factors for Small Watersheds for 50% AEP or Greater 1-day Design Storms Table 2.4 Runoff Coefficients for Non-Zoned Areas Figure 2.3 Process for C Value Adjustment Table 2.5 Roughness Coefficients (Manning’s n) for Sheet Flow Figure 3.1 Dry Lane (Allowable Lane Encroachment) Table 2.6 Runoff Curve Numbers Figure 3.2 Parabolic Crown Street Flow Capacity Table 2.7 Composite Curve Number Example Figure 3.3 Grate Inlet Table 2.8 Sustainable Drainage Measure Curve Numbers Figure 3.4 Curb Inlet Table 3.1 Encroachment Limits Figure 3.5 Y-Inlet Table 3.2 Inlet Types Figure 3.6 Combination Inlet Table 3.3 Frequencies for Coincidental Occurrences Figure 3.7 Slotted Drain Inlet Table 3.4 Outlet Depth Conditions Figure 3.8 Storm Drain Inlets Table 3.5 Entrance Loss Coefficients Figure 3.9 Grate Perimeter Table 3.6 Riprap Apron Length Figure 3.10 Curb Inlets on Grade: Ratio of Intercepted to Downstream of Drop Structures Total Flow Table 5.1 Maximum Channel Velocities Figure 3.11 Y-Inlet Capacity Curves at Sag Point Table 6.1 Minimum Crown Width of Embankments Figure 3.12 Utility in Typical Streets Table 6.2 Constructed Wetland Volume Ratios Figure 3.13 Permeable Unit Pavement System Table 6.3 Constructed Wetland Area Ratios Figure 3.14 Sand & Organic Media Filters Table 9.1 Easement Widths Figure 3.15 Hydraulic Gradient Figure 3.16 Wye Connection Detail Figure 3.17 Head Losses in Laterals, Wyes, and Enlargements Figure 3.18 Head Losses for Junction Boxes, Manholes, and Bends Figure 3.19 Outlet Control Headwater for Culvert with Free Surface Figure 3.20 Outlet Control, Fully Submerged Flow Figure 3.21 Point at Which Free Surface Flow Begins vi Table of Contents Figure 3.22 Headwater due to Full Flow at Inlet and Free Figure 5.3 Length of Jump for a Rectangular Channel Surface at Outlet Figure 5.4 Drop Spacing Criteria Figure 3.23 Cross Sectional Area Based on Full Flow Figure 5.5 Baffle Chute Figure 3.24 Culvert with Overtopping Flow Figure 5.6 Checkdams Figure 3.25 Over-Embankment Flow Adjustment Factor Figure 5.7 Example Geometry for Channel Junction Figure 3.26 Roadway Overtopping with High Tailwater Figure 5.8 Channel Bottom Width Transitions Figure 3.27 Cross Section of Flow Over Roadway Figure 5.9 Superelevation Figure 3.28 Typical Performance Curve Figure 6.1 Stormwater Ponds Figure 3.29 Momentum Function and Specific Energy Figure 6.2 Constructed Wetlands Figure 3.30 Determination of Sequent Depth Figure 6.3 Rainwater Harvesting Figure 3.31 Solution for Circular Conduits Figure 6.4 Sump Area with Drywell Figure 3.32 Design of Riprap Apron under Minimum Tailwater Conditions Figure 6.5 Wet Well Figure 3.33 Design of Riprap Apron under Figure 6.6 Typical Cross Section Maximum Tailwater Conditions Figure 7.1 Natural Channel Setback Figure 3.34 Dimensionless Rating Curves for the Outlets of Figure 7.2 Bioengineering Rectangular Culverts on Horizontal and Mild Slopes Figure 7.3 Live Cribwalls Figure 3.35 Dimensionless Rating Curves for the Outlets of Circular Culverts on Horizontal and Mild Slopes Figure 7.4 Geogrid Figure 3.36 Relative Depth of Scour Hole Versus Froude Figure 8.1 Critical Levee Zone Number at Brink of Culvert with Relative Size of Figure 10.1 Outfall Ditch Survey less than 3ft Riprap as a Third Variable Figure 10.2 Outfall Ditch Survey Example less than 3ft Figure 3.37 Details of Riprap Outlet Basin Figure 10.3 Outfall Ditch Survey more than 3ft Figure 3.38 SAF Stilling Basin Figure 10.4 Outfall Ditch Survey Example more than 3ft Figure 3.39 Contra Costa Basin Figure 10.5 Floodplain Location Methods Figure 3.40 Baffled Outlet Detail Figure 10.6 Culvert Survey Detail Figure 4.1 Model Cross-Section Locations Figure 10.7 Culvert Survey Example Figure 4.2 Bridge Profile with Cross Section Location Figure 10.8 Minor Drainage Wingwall Figure 5.1 Hydraulic Jump Figure 10.9 Catch Basin Locations Figure 5.2 Hydraulic Jump Conjugate Depth – Horizontal, Rectangular Channel

Dallas Drainage Design Manual vii

SECTION 1 Introduction

Dallas Drainage Design Manual 1 1.1 1.2 PURPOSE SCOPE

The purpose of this Drainage Design Manual is to establish The guidelines contained in this manual have been standard principles and practices for designing drainage developed from a comprehensive review of basic facilities in the City of Dallas. This manual is for use by all design technology as contained in various engineering City of Dallas departments, consultants employed by the publications, and through the City’s historical design City, and engineers for private development in the City. It is and maintenance experience. This manual addresses not intended to limit the design capabilities or engineering storm drainage situations that are generally typical of judgment of the design professional or the use of new the City of Dallas and its immediate geographical area. technical developments in engineering. Responsibility for Accepted engineering principles are applied to these design remains with the design engineer. situations in detailed documented procedures. Criteria presented herein are intended to be consistent with federal and state regulations, including but not limited to the United States Army Corps of Engineers (USACE) authority concerning the Clean Water Act and the City’s participation as a cooperating technical partner with the Federal Emergency Management Agency (FEMA) under the Community Rating System (CRS). The documentation is not intended to limit initiative but rather is included to provide a standardized format to aid in design and as a record source. Unusual circumstances or special designs requiring variances from the standards within this manual may be coordinated and approved by the applicable Department Director. All requests for a variance must be submitted in writing to the Department Director. Pre- development meetings to discuss strategies and concepts are recommended and may be required.

Additional information and development regulations regarding drainage design can be found in the Development Code - Article V Sec. 51A-5.100-5.105.

Additional federal and local regulations may apply to a project. The project and regulating documents should be reviewed in their entirety to determine applicability. All other applicable regulations and permit requirements must be fulfilled to obtain approval from the City of Dallas. A list of reference regulatory documents is included in Appendix A.1.

2 Section 1 Introduction 1 INTRODUCTION 2 HYDROLOGY 3

1.3 ROADWAY DRAINAGE DESIGN OVERVIEW 4

This manual is divided into the following 11 sections: BRIDGE HYDRAULIC DESIGN

Section 1 Introduction is a general discussion of the intended Section 8 Floodplain and Sump Design Requirements is a use of the material and an explanation of its organization. discussion of design criteria and regulatory requirements within 5 areas defined by the City of Dallas as floodplain or sumps. DESIGN Section 2 Hydrology is a discussion of hydrologic OPEN CHANNEL methods and analysis criteria for the determination of Section 9 Other Regulatory Requirements lists design discharges, volumes, and hydrologic impacts of requirements for permitting, easements, and submittals to the development of a site.

other regulatory agencies. 6 DRAINAGE

Section 3 Roadway Drainage Design lists criteria and Section 10 Submittal Requirements provides City of Dallas STORAGE DESIGN parameters for the design of roadway drainage elements, requirements regarding construction plans, as well as including inlets, storm drains, culverts, and outfalls, and helpful information to assist the design engineer and outlines the design procedures and methodology used by expedite the plan review process. the City of Dallas. Section 11 Operation and Maintenance includes 7 Section 4 Bridge Hydraulic Design includes methodology consideration and parameters for maintenance of CONTROL MEASURES and criteria for the hydraulic design of bridges. stormwater infrastructure EROSION & SEDIMENT

Section 5 Open Channel Design includes methodology, Appendices contain applicable regulations, charts and design procedures, and criteria for the hydraulic design of tables to assist with computations, a list of reference open channels. documents, a list of acronyms and definitions, guidelines

& procedures, and checklists & forms. 8 Section 6 Drainage Storage Design includes methodology,

design procedures, and criteria for drainage storage systems. A list of design resources and approved software can be FLOODPLAIN & SUMP DESIGN REQUIREMENTS found on the City of Dallas website. Section 7 Erosion and Sediment Control Measures includes temporary erosion control guidance, and methodology and criteria for permanent channel erosion

and sediment control measures. 9 REQUIREMENTS OTHER REGULATORY OTHER REGULATORY 10 SUBMITTAL SUBMITTAL REQUIREMENTS 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 3 APPENDICES Dallas is an urban environment, therefore aesthetic design must be considered. The City of Dallas encourages the preservation of natural channels and floodplains, tree canopy buffers, and natural drainage patterns where possible. Structural components should be designed to integrate with the project surroundings. 1.4 Figure 1.1 Drainage Design Process 1 Determine the contributing watershed area INTEGRATING

DRAINAGE 2 Assess eisting hydrologic and hydraulic conditions 1.4.1 Drainage Design Process

Drainage should be considered at the beginning of any 3 design process. The following general process should be Assess potential impacts to osite proper used for drainage design for a site. City capital projects ties and eisting drainage acilities must follow same process as private developments.

1.4.2 Drainage Design Considerations 4 repare proposed drainage plan A significant percentage of developed land within the City of Dallas is comprised of impervious area, including buildings, roads and sidewalks. The increased impervious area in the City impacts natural drainage and contributes 5 to increased rates and volumes of runoff and processes Consider sustainable drainage design measures such as infiltration, evapotranspiration, and groundwater to improe water quality mitigate urban drainage recharge. Unmitigated development can lead to increased impacts and reduce detention requirements flooding, system exceedance, channel and bank erosion, and stormwater pollution. The City of Dallas encourages that both water quantity and quality be taken into account for any design both during and after construction. 6 Construction plans must consider erosion control and Sie proposed drainage acilities have procedures in place to prevent stormwater pollution. Permits shall be acquired in accordance with federal, state, and local regulations. 7 Water quality and quantity is also important for street design. Compare proposed condition results against The City of Dallas encourages a holistic approach to street requirements o this manual design, integrating the elements of multi-modal transportation, drainage, walkability, and aesthetics. Refer to the Street Process and Street Design Manuals for guidance on the street 8 design process. By managing stormwater with sustainable Reise plan and repeat rom step 3 as necessary drainage measures before it enters the conveyance system, to meet requirements o this manual positive water quantity and quality impacts can be achieved, especially for smaller storms. Additional benefits include reducing the heat island effect, improving air quality, and increasing the value and aesthetics of property.

4 Section 1 Introduction 1

If a pre-development meeting is required or requested, INTRODUCTION 1.4.3 Defining a Project the following items, at a minimum, must be reviewed and prepared by the designer prior to the meeting. Other items

When considering the hydrologic impacts of a project, 2 may be necessary depending on site and project conditions.

the entire contributing drainage area, adjacent property, HYDROLOGY and upstream and downstream conditions must be taken -- Topographic workmap into account. The project size refers to the size of the entire developed project, not the individual phases of the -- Conceptual layout project. The cumulative effects of a project with multiple -- Existing flood studies or models 3

phases should be taken into consideration. ROADWAY

-- FEMA flood maps if applicable DRAINAGE DESIGN 1.4.4 Sustainable Design Guidelines -- Upstream Drainage Area Delineation The methods and policies outlined in this document are the -- Upstream and downstream conditions and capacity 4

minimum requirements for drainage for the development of BRIDGE a site. The City of Dallas encourages innovation, sustainable See Section 10 for project submittal requirements. HYDRAULIC DESIGN drainage practices, and project review relative to more sustainable design by utilizing project rating systems such 1.4.6 Design Software as LEED and Envision. Drainage requirements within these 5

programs should be coordinated with other street and Software that facilitates the design of drainage facilities DESIGN

facility plans to meet the minimum requirements described can be found on the City of Dallas website. Depending OPEN CHANNEL in this manual. In addition to contributing towards on the analysis being performed by the design engineer, greater community resilience, these guidelines are also certain applications may require the use of specific requirements of the City’s municipal separate storm sewer software and modeling techniques. This should be system permit under Texas Pollutant Discharge Elimination discussed in the pre-development meeting. 6 System (TPDES) and our participation in the FEMA CRS DRAINAGE STORAGE DESIGN program. 1.4.5 Pre-Development Meeting 7 A pre-development meeting is encouraged for all projects within the City of Dallas. It is valuable to spend time in CONTROL MEASURES discussion with the City to address any concerns at the EROSION & SEDIMENT beginning of a project, verify an understanding of design criteria as it applies to the project, and discuss any unusual elements of the project. A pre-development meeting shall be required if any of the conditions below apply: 8 -- The project is private and has a size greater than 5 acres FLOODPLAIN & SUMP DESIGN REQUIREMENTS -- The project site is within 1/4 mile of a defined sump area (refer to City of Dallas website for map of sump locations) -- The project site is within 100 feet of a stream 9 -- The project lies within a floodplain according to the REQUIREMENTS

current floodplain ordinance. Consult Article V for OTHER REGULATORY floodplain application meeting requirements. -- The project is within the Escarpment Zone or a geologically similar area 10 SUBMITTAL SUBMITTAL

-- The downstream system does not have adequate capacity REQUIREMENTS -- Innovative design approaches are being used 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 5 APPENDICES

SECTION 2 Hydrology

Dallas Drainage Design Manual 7 See Table 2.2 for a summary of design storms for drainage elements.

Table 2.2 Design Storms for Drainage Elements

Design Annual Design Standard Element Chance Design Storm 2.1 Detention/ 1%, 2%, 10%, No increase in peak discharge Retention 50% No increase in erosive velocity Culverts 1% Convey with a minimum of 2 feet GENERAL of freeboard between top of curb and HGL This section contains the minimum hydrologic design Bridges 1% Convey with a minimum of 2 feet criteria to be followed in the design of storm drainage of freeboard between low chord of facilities and demonstrates the design procedures to be bridge and HGL used on drainage projects in the City of Dallas. Open 1% Convey with a minimum of 2 feet All new systems will be designed to accommodate the 1% Channels of freeboard below top of bank, or annual chance storm event or flood of record. See Table in spreading creek or river areas, 2.1 for a comparison of annual chance storm events to convey with 2 feet of freeboard annual recurrence intervals. For rainfall, this is also known below top of conveyance section as the annual exceedance probability (AEP). covered by easement or regulated floodplain Table 2.1 Probability of Exceedance No increase in erosive velocity

Annual Chance Annual Recurrence Interval (as percent) 50% 2-year 10% 10-year 2% 50-year 1% 100-year 0.2% 500-year

8 Section 2 Hydrology 1

Table 2.3 Runoff Coefficients for Zoned Areas INTRODUCTION

Zone Zoning District Name Runoff Coefficient 2 A (A) Agriculture 0.30 HYDROLOGY R – 1ac (A) Residential 0.45 R – 1/2ac (A) Residential 0.45 3

2.2 R – 16 (A) Residential 0.55 ROADWAY R – 13 (A) Residential 0.55 DRAINAGE DESIGN HYDROLOGY R – 10 (A) Residential 0.65 R – 7.5 (A) Residential 0.70 4

The Rational Method for computing storm water runoff R – 5 (A) Residential 0.70 BRIDGE

design rates and volumes can be used for hydrologic HYDRAULIC DESIGN D (A) Duplex 0.70 analysis of facilities when the total contributing drainage area is less than 100 acres. For all other drainage areas, TH – 1 (A) Townhouse 0.80 runoff is to be calculated using the Soil Conservation

TH – 2 (A) Townhouse 0.80 5

Service (SCS) Unit Hydrograph Method, the preferred DESIGN method for design. TH -3 (A) Townhouse 0.80 OPEN CHANNEL CH Clustered Housing 0.80 Coordination with the Director is required for the use of other methods, including Snyder’s method. If modifying an existing MF – 1 (A), MF - 2 Multifamily Residential 0.80 regulatory model performed using a different methodology, (A), 6 continued use of that methodology may be allowed as MF - 3 (A), MF - 4 (A) DRAINAGE STORAGE DESIGN approved by the Director. MH (A) Mobile Home 0.55 NO (A) Neighborhood Office 0.80 2.2.1 Rational Formula LO – 1, LO - 2, LO - 3 Limited Office 0.90 The Rational Formula for computing peak runoff rates is MO – 1, MO - 2 Midrange Office 0.90 7 as follows:

GO (A) General Office 0.90 CONTROL MEASURES EROSION & SEDIMENT Q = CIA (Equation 2.1) NS (A) Neighborhood Services 0.90 CR Community Retail 0.90 Q = Runoff rate (cfs) RR Regional Retail 0.90 C = Runoff coefficient CS Commercial Service 0.90 8

I = Rainfall intensity (in/hr) LI Light Industrial 0.90 FLOODPLAIN & SUMP DESIGN REQUIREMENTS A = Drainage area (ac) MU Industrial Research 0.90 IM Industrial Manufacturing 0.90 2.2.1.1 Runoff “C” Value CA – 1 (A), CA - 2 (A) Central Area 0.95 9 Runoff coefficients for existing and proposed conditions MU – 1 Mixed Use - 1 0.80 REQUIREMENTS are shown in Table 2.3 and 2.4. Existing land use shall MU – 2 Mixed Use - 2 0.80 OTHER REGULATORY be used for determining existing conditions. All off-site runoff calculations shall be based upon a fully developed MU - 3 Mixed Use - 3 0.90 watershed and proposed zoning. Larger coefficients may MC - 1, MC - 2, Multiple Commercial 0.90 be used if considered appropriate by the Director. See MC - 3, MC - 4 10 SUBMITTAL SUBMITTAL

Section 2.3.3 for potential reduction to these factors if the REQUIREMENTS UC - 1, UC - 2, Urban Corridor 0.90 drainage plan incorporates sustainable drainage design UC - 3 measures. P (A) Parking 0.95 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 9 APPENDICES Table 2.4 Runoff Coefficients for Non-Zoned Areas The definition for time of concentration T( c) considers the geometry, geology, soil type, land use, topography and other Land Use Runoff Coefficient “C” hydraulic characteristics of a watershed. Tc is defined as Church 0.8 the time required for runoff to travel from the furthest point, hydraulically, within the delineated area (or watershed) to School 0.7 the outlet of the drainage area (or watershed). Park 0.4 In order to provide a uniform and versatile equation which can Cemetery 0.4 be applied to most situations encountered in the City of Dallas, For shared access development, a composite value based the Tc shall be considered in four parts: 1) sheet flow; 2) on pervious and impervious cover must be calculated. shallow concentrated flow; 3) pipe flow; and 4) channel flow.

The C value estimates may be adjusted to account for Combining time of concentration for sheet flow, shallow the impact of sustainable drainage measures on peak concentrated flow, pipe flow, and channel flow yields the discharge rates for Rational Method calculations. C value following equation: adjustment factors should only be used for determining T = T + T + T + T (Equation 2.3) runoff for the 50% annual chance storm event, as c cs csc cp cc sustainable drainage measures are only typically used to T = Time of concentration (hr) reduce runoff for smaller storm events and will usually c Time of concentration representing sheet flow (hr) have minimal effect on larger storms. Tcs = Time of concentration representing shallow Rain Gardens & Bioretention Tcsc = concentrated flow (hr) If the design water quality volume to be treated by the measure is determined and it is designed to treat 100% Time of the concentration representing pipe flow (hr) Tcp = of the design water quality volume, the following equation can be used to determine an adjusted factor ( ) for T = Time of concentration representing stream or C Cadj cc the 50% annual chance and smaller events. channel flow (hr) C = C * 1 - 1_ P (Equation 2.2) adj ( 2 WQ) Detailed discussion of each component is provided in the following paragraphs. If the computed T is less than C = Adjusted proposed runoff coefficient c adj 10 minutes, then a minimum of 10 minutes shall be Tc C = Proposed runoff coefficient without consideration of used. This condition occurs often, though not always, when computing the for an inlet in a residential or sustainable drainage measures Tc commercial area. P = Design water quality precipitation (1.0 - 1.5 inches) WQ Sheet Flow See example in Appendix A.2. Sheet flow is flow over a planar surface with a depth up to Permeable Pavement & Pavers 0.1 feet. The following equation can be used to estimate the sheet flow travel time. Ordinarily, sheet flow will occur for a For permeable pavement and pavers, the C value can be distance of 50 to 100 feet. For sheet flow across impervious adjusted by treating the area of the permeable pavement as surfaces, the maximum sheet flow length shall be 50 feet. park area ( value of 0.4) in rational method calculations, C 0.007(nL)0.8 for the 50% annual chance and smaller storm events only. T = ______ (Equation 2.4) cs 0.5 0.4 (P2 ) (S0 ) Time of concentration representing sheet flow (hr) 2.2.1.2 Rainfall Intensity (i) Tcs = The rainfall intensity value “i” is the intensity for a n = Manning’s roughness coefficient (reference Table 2.5) duration equal to the time of concentration (T ). Rainfall c L = Flow length (ft) (≤ 100 ft) intensities can be found online using National Oceanic and Atmospheric Administration’s (NOAA) National P = 2-year (50% AEP) 24-hour rainfall (in) Weather Service (NWS) Precipitation Frequency Data 2 Server (PFDS). Slope of land surface (ft/ft) S0 = Table 2.5 includes Manning’s n values, or roughness 2.2.1.3 Time of Concentration (Tc) coefficients, for sheet flow. These ‘n’ values are higher Design rainfall intensities are dependent upon the time than typical open channel flow values to account for the of concentration contributing to the drainage facility. impact of raindrops and drag forces on flow over a plane with depths less than 0.1 feet. 10 Section 2 Hydrology 1

Table 2.5 Roughness Coefficients (Manning’s n) for Sheet Flow The nomograph provided in Figure 2.1 may be used INTRODUCTION to estimate shallow concentrated flow velocity as it is Surface Description 1 n a graphical representation of the unpaved and paved 2 Smooth surfaces equations provided. HYDROLOGY (concrete, asphalt, gravel, or bare soil) 0.011 Figure 2.1 Shallow Concentrated Flow Average Velocity Fallow 50 (no residue) 0.05 3

Cultivated soils: ROADWAY DRAINAGE DESIGN Residue cover < 20% 0.06 Residue cover > 20% 0.17 0

Grass: 4 Short grass prairie 0.15 BRIDGE HYDRAULIC DESIGN Dense grasses2 0.24 10 Bermuda grass 0.41 5

Range 06 DESIGN Natural 0.13 OPEN CHANNEL Woods3 04 Light underbrush 0.40

Dense underbrush 0.80 DRAINAGE STORAGE DESIGN 1 The n values composite information by Engman (1986) 0 2 Includes species such as bluestem grass, buffalo grass, grama grass, and native grass mixtures 7 3 When selecting n, consider cover to a height of about 0.1 ft. This is 01 the only part of the plant cover that will obstruct sheet flow. CONTROL MEASURES EROSION & SEDIMENT Shallow Concentrated Flow 005 The equation for shallow concentrated flow travel time is 1 4 6 10 0 as follows:

L 8 ______sc (see enlarged ﬁgure in Appendix A.7) Tcsc = (Equation 2.5) (see enlarged figure in Appendix A.7) 3600V

sc FLOODPLAIN & SUMP Time of concentration representing shallow DESIGN REQUIREMENTS Tcsc = concentrated flow (hr) The equation for travel time in a pipe is as follows: L L = Length of shallow concentrated flow (ft) T = ______ p (Equation 2.8) sc cp

3600V 9 V = Average velocity (ft/s) p sc T = Time of concentration representing pipe flow (hr)

cp REQUIREMENTS These equations can be used to determine average (for simplification purposes, a full flow condition may be OTHER REGULATORY velocities, including for slopes less than 0.005 ft/ft. assumed in the pipe)

0.5 Unpaved V = 16.13 (S) (Equation 2.6) Length of pipe (ft) sc Lp = 10

0.5 SUBMITTAL Paved V = 20.33 (S) (Equation 2.7) V = Average velocity of the design discharge in the pipe, REQUIREMENTS sc p Average velocity for shallow concentrated flow (ft/s) calculated per Manning’s equation (ft/s) Vsc = Refer to Appendix A.3 for pipe ‘n’ values. S = Slope of land surface (ft/ft) 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 11 APPENDICES Channel Flow 2.2.2 Hydrograph Methods The equation related to channel flow relates velocity, length, and time: 2.2.2.1 SCS Unit Hydrograph Method L ______c Tcc = (Equation 2.8) 3600V When a drainage area under consideration is greater than c or equal to 100 acres, the City of Dallas recognizes the Soil T = Time of concentration representing stream or cc Conservation Service (SCS) Unit Hydrograph Method for channel flow (hr) determining rates and volumes of stormwater runoff. The City recognizes the use of approved software (a list of which L = Effective hydraulic length of ditch or channel (ft) c can be found on the City of Dallas website.) The City of Dallas maintains hydrologic models on most primary and V = Average velocity of ditch or channel flow (ft/s) c some secondary channels in Dallas. Where the City has an existing hydrologic model, it should be utilized unless the The velocity (Vc) in the channel can be obtained directly from the existing hydraulic model. When velocity results Director approves development of a new model. Models that are not available for a reach, channel velocity can be are currently in use in an area should be utilized for future estimated using Manning’s formula: projects. Any variances must be approved by the Director. 2/3 1/2 A unit hydrograph is the time discharge relationship, Vc = (1.49 / n) (R) (S) (Equation 2.10) defined at a given point along a water course, which Velocity in channel (ft/s) Vc = results from a storm producing one inch of runoff uniformly distributed over the watershed. The SCS Unit Hydrograph n = Roughness coefficient (see Appendix A.3) Method computes the unit hydrograph for a given area and then converts it to the flood hydrograph theoretically R = Hydraulic radius (ft) equal to A / Pw resulting from a given rainfall event. The input required to compute the design flood hydrograph includes drainage A = Cross sectional flow area (ft2) D area, lag time, runoff curve number, rainfall information for the design storm, and a dimensionless unit hydrograph. Wetted perimeter (ft) Pw = S = Slope of the hydraulic grade line (ft/ft)

Figure 2.2 Areal Reduction Factors for Small Watersheds for 50% AEP or Greater 1-day Design Storms

1.00

0.95

0.90

0.85

0.80 D

0.75

0.70

D D R 0.65 0.01 0.1 1 10 100 2 (see(see enlargedenlarged figure ﬁgure inin Appendix A.7)G)

12 Section 2 Hydrology 1

Rainfall of the soil (NRCS. 2009. Part 630, National Engineering INTRODUCTION Handbook, Chapter 7, Hydrologic Soil Groups, (210-VI- 24-hour rainfall depths can be found online using NOAA’s NEH)). These four groups are generally described as follows: National Weather Service Precipitation Frequency Data 2

Server. Areal Reduction Factors may be used to account Group A Soils: generally consist of deep sands and other HYDROLOGY for non-uniform distribution of rainfall in large watersheds. soils that have a low runoff potential when thoroughly wet, See Figure 2.2 for Dallas adjustment factors. Information due to high hydraulic conductivity. pertaining to design storm duration and distribution will

be provided by the Director where the City has an existing Group B Soils: generally consist of soils with moderately 3 hydrology model. Where new models are being developed, low runoff potential when thoroughly wet. ROADWAY

SCS Type III 24-hour rainfall distribution will be used. DRAINAGE DESIGN Group C Soils: generally have a moderately high runoff Drainage Area Delineation potential when thoroughly wet, because water transmission through the soil is somewhat restricted.

Drainage area delineations must utilize the most accurate 4 and recent ground data available for the area. The entire Group D Soils: generally have a high runoff potential when BRIDGE watershed draining to a property must be considered, not thoroughly wet. HYDRAULIC DESIGN just the area within the project or property boundaries. The area of consideration shall be to the point where Surficial soils data can be obtained from County Soil Maps prepared by the NRCS, however, NRCS soil data should the drainage area controlled by the detention or storage 5 facility comprises 10% of the total drainage area. For not be substituted for geotechnical data for drainage DESIGN example, if the structural control drains 10 acres, the area infrastructure design. Additionally, hydrologic soil groups OPEN CHANNEL of consideration ends at the point where the total drainage for borrow material, mixed and or disturbed site soils shall area is 100 acres or greater. The drainage area delineation be determined through appropriate geotechnical field must also contain any contributing storm sewer systems. investigation. Curve numbers associated with hydrologic soil group and cover type are provided in Table 2.6. 6 DRAINAGE

In some instances, drainage area subdivision may be STORAGE DESIGN appropriate. Examples of such scenarios include but are Equation 2.11 can be used to estimate direct runoff from not limited to: a 24-hour storm rainfall. (P-0.2S)2 -- Drainage areas with significantly varying C values / Q = ______ (Equation 2.11) P+0.8S

curve numbers 7 ______1000 -- Significantly different slope patterns S = (Equation 2.12) CONTROL MEASURES CN-10 EROSION & SEDIMENT -- A detention facility within a contributing area Q = Accumulated direct runoff (in)

-- Intermediate points of interest for facility design P = Design precipitation (in)

-- Stream confluences CN = Runoff curve number 8 -- Infrastructure such as dams and levees S = Maximum potential retention (in) FLOODPLAIN & SUMP DESIGN REQUIREMENTS Subdivision of drainage areas will require detailed routing in The values in Table 2.6 are based on average percent order to incorporate the effects of travel time and floodplain impervious area for different land uses. Composite curve storage between the subdivided basins. The following numbers can be developed for drainage areas with

sections include approved hydrograph routing methods. multiple land uses. They can be developed in two ways: 9

1. An open space curve number can be applied for the REQUIREMENTS Runoff Curve Number OTHER REGULATORY entire basin area along with a percent impervious area. Rainfall runoff potential, presented in the form of a runoff The composite curve number can be computed by hand. curve number (CN), is an expression of the runoff potential for a given land use and the runoff potential of the underlying 2. A weighted curve number is developed for each land 10 soil. Higher CN values correlate to higher runoff potential. The use based on the percentage of total land area that it SUBMITTAL National Engineering Handbook by the National Resource encompasses. See Table 2.7 for the calculation of a REQUIREMENTS Conservation Service (NRCS, formerly Soil Conservation composite curve number. Service, SCS) provides the definitions for four hydrologic soil groups, based upon hydrologic conductivity characteristics 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 13 APPENDICES 1 Table 2.6 Runoff Curve Numbers 1 Average runoff conditions and initial abstraction = 0.2S Curve numbers 2 The average percent impervious area shown was used to develop Avg % for hydrologic the composite CNs. Other assumptions are as follows: impervious Cover Description impervious soil groups area2 areas are directly connected to the drainage system, impervious areas A B C D have a CN of 98, and pervious areas are considered equivalent to Cultivated Land: open space in good hydrologic condition. If the impervious area is not connected, the SCS method has an adjustment to reduce the effect. Without conservation treatment 72 81 88 91 3 With conservation treatment 62 71 78 81 CNs shown are equivalent to those of pasture. Composite CNs may be computed for other combinations of open space cover type. Pasture or range land: Poor condition 68 79 86 89 Table 2.7 Composite Curve Number Example Good condition 39 61 74 80 Fraction of Weighted Curve Meadow: Total Land Curve Number (Fraction Land Use Area Number area x CN) Good condition 30 58 71 78 Residential 1/8 acre 0.80 85 68 Wood or forest land: Soil Group B Thin stand, poor cover 45 66 77 83 Meadow Good 0.20 71 14 Good cover 25 55 70 77 condition Soil Group C Open space (lawns, parks, golf Total Composite Curve Number = 68 + 14 = 82 courses, cemeteries, etc.)3 Poor condition (grass cover <50%) 68 79 86 89 The curve numbers in Table 2.8 can be used for applicable sustainable drainage measures for the 50% Fair condition 49 69 79 84 annual chance storm event only. (grass cover 50% to 75%) Good condition (grass cover >75%) 39 61 74 80 Table 2.8 Sustainable Drainage Measure Curve Numbers Impervious areas: Practice/Land Type Curve Number Paved; curbs and storm drains 98 98 98 98 Permeable Paving, Permeable Unit Pavement 40 (excluding right-of-way) System, Porous Pavers Paved; open ditches 83 89 92 93 Rain Gardens/Bioretention 35 (including right-of-way) Gravel (including right-of-way) 76 85 89 91 Lag Time Dirt (including right-of-way) 72 82 87 89 Lag time is a required input for the SCS unit hydrograph method. Lag time is defined as difference in time between Urban districts: the peak of the rainfall event and the peak discharge of Commercial and business 85% 89 92 94 95 the resulting hydrograph. Lag time can be determined by the equation below. Industrial 72% 81 88 91 93 Residential districts by avg lot size: Tlag = 0.6 Tc (Equation 2.13) T = Lag time (hr) 1/8 acre or less (town house) 65% 77 85 90 92 lag Time of concentration (hr) ¼ acre 38% 61 75 83 87 Tc = 1/3 acre 30% 57 72 81 86 Discussion of methodology to estimate the time of ½ acre 25% 54 70 80 85 concentration for a basin is provided in Section 2.2.1.3. If a recorded flood hydrograph is available, the lag time 1 acre 20% 51 68 79 84 may be estimated from the hydrograph parameters rather 2 acres 12% 46 65 77 82 being derived empirically. Developing urban areas and newly 77 86 91 94 graded areas (previous areas only, 2.2.2.2 Use of Other Hydrograph Methods no vegetation) There may be the need for the use of the Snyder Unit Hydrograph method or the NUDALLAS method on a case by case basis, dependent on the methods used in the 14 Section 2 Hydrology existing models. 1

2.2.2.3 Flood Routing Muskingum-Cunge Method INTRODUCTION The Muskingum-Cunge method provides a simplified Flood routing is an iterative process that determines flood estimation of floodplain storage to reflect hydrograph 2 wave (flow) travel time and attenuation using hydrologic attenuation for locations where detailed hydraulic HYDROLOGY or hydraulic routing methods and is normally required modeling is not available for use in the Modified Puls when drainage areas are subdivided. Flood routing can method. The standard channel configuration may be used be determined using approved hydrologic software, a for man-made channels with simple prismatic cross- list of which can be found on the City of Dallas website.

sections. The 8-point cross section method should be 3 Applicability and limitations for each of the methods used for natural channels. Refer to HEC-HMS Technical ROADWAY indicated in the computer program’s technical reference Reference manual for guidance on this method. DRAINAGE DESIGN manual should be considered. The Modified Puls method is the City-preferred flood routing method and shall be Lag Method used for all streams located within a FEMA-designated

Zone AE floodplain. The Modified Puls method must This method may only be used if the following condition is met: 4

BRIDGE also be used for any stream/floodplain where significant ___ L < 2 ∆ t (Equation 2.18) backwater is expected or significant overbank storage V HYDRAULIC DESIGN exists. Other approved methods suitable for streams L = Reach length (ft) where the Modified Puls is not required are also Channel velocity (ft/s) discussed in the following subsections. Methods not listed V = 5 below may only be used with approval of the Director. DESIGN ∆t = Hydrograph time interval (min) OPEN CHANNEL Channel Routing It should be noted that the Lag method is most Approved hydrologic channel routing methods include the appropriate for short reaches on small streams and does

Modified Puls, Muskingum-Cunge, Lag, and Kinematic not account for flood volume attenuation. The Lag method 6

Wave methods. See the descriptions below for guidance simply translates the inflow hydrograph in time to account DRAINAGE on appropriate use of methods. Refer to HEC-HMS and for the time it takes to travel through the reach. STORAGE DESIGN HEC-RAS user manuals for full description of methodology. Kinematic Wave Method Modified Puls Method This method is a simplified hydraulic routing technique This method requires detailed hydraulic modeling that can be computed using HEC-HMS, SWMM, or 7 (HEC-RAS) to compute a storage-outflow relationship. other approved hydrologic software. It is appropriate for CONTROL MEASURES Additionally, an input of routing steps or subreaches will channels that have been modified to have a regular shape EROSION & SEDIMENT need to be determined. The number of routing steps (n) and uniform slope. can be computed by the following: Reservoir Routing L / V n = ____ w (Equation 2.17) ∆t Hydrograph routing through a reservoir can be computed 8 with the Modified Puls method. A detailed description n = Number of routing steps (dimensionless)

of level-pool routing can be found in the HEC-HMS FLOODPLAIN & SUMP DESIGN REQUIREMENTS L = Reach length (ft) Technical Reference manual and other manuals from the approved software list found on the City of Dallas Average flood wave velocity (ft/s) Vw = website. A storage-outflow relationship is required for this routing method. The storage-outflow relationship is

∆t = Hydrograph time interval (min) dependent upon the characteristics of the storage facility 9 and the outlet and spillway. For simple outflow structures, Alternatively, travel time can be pulled directly from REQUIREMENTS outlet configurations can be entered directly into most OTHER REGULATORY HEC‑RAS to replace L/V w hydrologic modeling software. Data from a hydraulic To run a Modified Puls model, a steady flow model must program such as HEC-RAS can be used to run multiple steady-state water surface profiles to determine outflow

be created first in HEC-RAS, with several different flow 10 values for corresponding storage volumes/elevations for profiles ranging from low to higher than expected flows to SUBMITTAL create a rating curve. See the HEC-RAS User’s Manual for complex outlet structures. REQUIREMENTS guidance on how to run a Modified Puls model. 2.2.2.4 Hydrograph Time Interval A storage-discharge table can be created for each reach, showing the storage loss associated with each flow profile Determination 11 OPERATION & OPERATION for every reach that can be used as input data to the HMS For an SCS Unit Hydrograph model, computational time MAINTENANCE model to properly model storage loss as runoff is routed intervals must be less than 29% of the lag time. through a reach. Dallas Drainage Design Manual 15 APPENDICES 2.2.2.5 Gage Data and Calibration Methods When United States Geological Survey (USGS) gage data is available at a site, a statistical analysis of the data can be performed to determine hydrologic design information. If the site is near a gage station on the same stream and has similar hydrologic conditions, the data can be directly applied in a flood frequency analysis. If the site is on the same stream, but not near the gage station, an in-depth 2.3 statistical analysis, described in the Texas Department of Transportation (TxDOT) Hydraulic Manual, can be used in the flood frequency analysis.

Refer to the City of Dallas website for a list of gage DETENTION / stations in the Dallas area. If applicable, gage data from these sites may be used in a stream flow analysis. Each RETENTION ANALYSIS of these gages is affected by regulation or diversion, so consideration must be given to upstream conditions when streamflow data is used for analysis. 2.3.1 Design Objectives

If gage data is available for the site, models should be Stormwater detention is sometimes required to temporarily calibrated to best fit the observed data. The HEC-HMS impound (detain) excess storm water, thereby reducing manual provides detailed explanations of calibration peak discharge rates. parameters, which include discharge, pool elevation, and cumulative precipitation. The purpose of detention is to impound water for a certain period of time before it drains or overflows into a storm 2.2.2.6 Storage Options sewer system or channel. Detention ponds can be designed to remain dry in between storm events (Dry Detention Storage within a drainage basin that acts to change the pond) or maintain a permanent wet pool for aesthetics or shape and peak value of a hydrograph is not always recreation (Wet Detention pond). Retention ponds impound associated with a formalized detention facility. Natural water while allowing infiltration through porous soils so that storage from small depressions can impact peak runoff all runoff is retained and no runoff is passed downstream. rates. This type of storage can be accounted for within unit hydrograph procedures as described in the HEC‑HMS For all projects, runoff must be detained to existing levels Technical Reference manual. Storage within most urban with no increase in peak discharge and no increase in erosive floodplains can be modeled with the Modified Puls routing velocity downstream of the delineated project site for the method. Storage within a drainage basin is sometimes 1%, 2%, 10%, and 50% annual chance storm events. An a result of undersized storm drain systems or a lack increase in discharge or erosive velocity is considered not to of adequate natural conveyance capacity within the occur when the following conditions are met: watershed. The impact of this storage can be significant. 1. When a downstream analysis (See Section 2.3.2) has Adequate assessment of the impact of this storage may not been performed: necessitate the use of a 2-dimensional hydrodynamic model such as SWMM or InfoWorks. The use of a a. Zero increase for the 1%, 2%, 10%, and 50% 2D hydrodynamic model is not only necessary in some annual chance discharges cases to adequately assess existing conditions discharges, it 2. When a downstream analysis (See Section 2.3.2) has can be critical to understanding the impact that stormwater been performed: conveyance improvement projects (which tend to eliminate a. Zero increase for the 1%, 2%, and 10% annual these storage areas) can have upon downstream peak chance discharges discharges. A list of approved 2D hydrodynamic modeling software can be found on the City of Dallas website. Pre- 3. Channel velocities do not exceed the permissible design meeting discussions of whether this type of modeling maximum velocity at any location within the is appropriate on a specific project are encouraged. downstream assessment for the 1%, 2%, 10%, or 50% annual chance events. Exceptions to these Floodplain valley storage can also impact routing and criteria require certified geotechnical / geomorphic the shape of hydrographs. Loss of valley storage can studies that provide documentation that the higher have an adverse downstream impact. Refer to Article V velocities will not cause erosion. Section 51A‑5.100 for valley storage requirements.

16 Section 2 Hydrology 1

Compliance with the threshold conditions used to 2.3.3.1 Modified Rational Method INTRODUCTION determine whether a project creates a significant impact on downstream discharges and velocities does not relieve The following steps are used to determine the minimum 2 the project from compliance with floodplain regulations, detention volume required for each design event: Article V Section 51A-5.100-5.105. HYDROLOGY Step 1 Infill developments and redevelopments are exempt from detention requirements if the parcel is less than 1 acre in Determine the 1% annual chance event peak runoff rate size and adds less than 5,000 square feet of additional on the site with existing conditions, which will be the 3 impervious surface relative to existing conditions. maximum allowable release rate (QA). The intensity for ROADWAY However, the use of rain gardens, pervious pavements the 1% annual exceedance probability (AEP) event can DRAINAGE DESIGN and other sustainable design measures are encouraged be found online using NOAA’s National Weather Service to minimize cumulative impacts from this type of Precipitation Frequency Data Server. development on a neighborhood scale. 4

Rainfall intensity for the 1% AEP storm event (in/hr) BRIDGE I1% = For roadway projects, determination of whether detention Time of concentration (See Section 2.2.1.3) (min) HYDRAULIC DESIGN is required shall be assessed for each roadway outfall. Tc = Roadway projects are exempt from detention requirements at an outfall if they add less than 10,000 square feet of Q1% = C * I1% * A (Equation 2.19) additional impervious area draining to that outfall. 5 Peak runoff for the 1% annual chance storm event DESIGN Q1% = All detention requires an easement. For plat regulations (cfs) OPEN CHANNEL and easement requirements, see Section 9.3. C = Runoff coefficient

2.3.2 Downstream Analysis A = Contributing drainage area (acres) 6 DRAINAGE

A downstream analysis is a tool for evaluating the impact Step 2 STORAGE DESIGN that a project may have on downstream discharges, water Determine inflow hydrographs for storms of multiple surface elevations, and velocities. The assessment must durations to determine the maximum volume required. extend downstream of a project outfall until the drainage Use 10-minute time increments and determine inflow area tributary to the project outfall comprises less than 7 rates. The last increment will be when the peak inflow is 10% of the downstream assessment area. less than the release rate found in Step 1. CONTROL MEASURES EROSION & SEDIMENT

2.3.3 Design Methodology For each time increment, determine the intensity (I ) and peak flow Q( ) using the following equation. Detention Storage – Basins without upstream detention areas and with drainage areas of 100 acres or less Qi = K * C * I * A (Equation 2.20)

prop 8 can be designed using the Modified Rational Method. Rainfall intensity (in/hr) (from online PFDS) This method estimates peak rates using the Rational I = FLOODPLAIN & SUMP DESIGN REQUIREMENTS Formula and storage requirements using inflow minus T = Time step duration (min) outflow hydrograph volume at the time of peak outflow. i Basins with drainage areas greater than 100 acres or Qi = Rate of discharge for the time step duration (cfs) where the Modified Rational Method is not applicable 1.0 for 10% AEP storm event or more frequent storm are to be designed using the Unit Hydrograph Method K = 9 and approved software, a list of which can be found on event; 1.15 for 1% AEP storm event or less frequent storm event. Application of the ‘ ’ factor provides a factor of REQUIREMENTS the City of Dallas website. Detention design that meets K OTHER REGULATORY the requirements for multiple design events (1%, 2%, safety to account for the inherent uncertainty associated 10%, and 50% annual chance) often requires complex with Modified Rational Method volume assessments. configurations for the outlet structure.

Proposed runoff coefficient 10 Cprop = SUBMITTAL SUBMITTAL REQUIREMENTS 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 17 APPENDICES Step 3 Water Quality Volume The first 1.5 inches of rainfall, which is the average depth Determine the storage volume required (Vreq ) for each time step duration using the following equations. of the 85th percentile storm for North Texas, is considered to be the water quality protection volume. The first flush V = V - V (Equation 2.21) of a storm event contains the highest load of pollutants req in out and sediment; therefore treating the first 1.5 inches of V = T * Q * 60 sec/min (Equation 2.22) stormwater runoff can provide significant water quality in i i benefits. Although recommended, not all sites may have the capability of treating the volume of runoff from V out = 0.5 *(Ti+ Tc )* QA* 60 sec/min (Equation 2.23) the first 1.5 inches of rainfall. A minimum of 1 inch of Required storage volume (ft3) Vreq = rainfall must be treated if a sustainable drainage measure is used. A design water quality precipitation between Volume in (ft3) Vin = 1.0 – 1.5 inches of rainfall can be chosen to determine 3 the design water quality volume to be treated by the V = Volume out (ft ) out sustainable drainage measure. T = Time step duration (min) i The water quality protection volume can be determined Rate of discharge for the time step duration (cfs) using the following methods. The proposed runoff coefficient Qi = “C” can be determined from Table 2.3 and Table 2.4. Time of concentration in the basin (min) Tc = Using a range from 1.0 - 1.5 inches as the design Maximum allowable release rate (cfs) QA = precipitation for water quality in North Central Texas, the design water quality capture depth in inches ( ) can DWQ Step 4 be calculated using the following formula: Determine the storm duration that produces the largest amount of storage required. This volume will be the design DWQ = PWQ * C (Equation 2.24) storage, with the maximum release rate calculated in Step 1. Design water quality capture depth (in) DWQ = Design water quality precipitation (1.0 – 1.5 in) 2.3.3.2 Adjustment for Sustainable Drainage PWQ = Measures C = Proposed runoff coefficient

The design water quality volume in cubic feet ( ) can Purpose VWQ be calculated using the following formula Sustainable drainage measures can have a significant impact on the overall hydrology of a site and are of V = D * A * (1 ft/12 in) (Equation 2.25) most benefit when used close to the point source of WQ WQ runoff and distributed uniformly rather than centralized. Design water quality volume (ft3) V = When implemented at a high level, sustainable drainage WQ measures can have a noticeable effect on smaller storms, A = Contributing drainage area (ft2) by reducing peak runoff and detaining stormwater for a short period of time. The hydrologic impact of sustainable Many sustainable drainage measures can be sized drainage measures can be calculated by adjusting curve based on a design water quality volume. Some measures numbers and storage volumes. are designed based on a flow capacity. Discussions of appropriate design approach for various sustainable There is no place in Dallas where sustainable drainage drainage measures are provided in Section 3 and Section 6. design cannot be considered, and it is encouraged relative to compliance with United States Environmental Adjustment for Detention Protection Agency (USEPA), Texas Commission on If an adjusted C factor is calculated based on the Environmental Quality (TCEQ), and FEMA regulatory implementation of sustainable drainage measures from requirements. Appropriate geochemical and geotechnical Section 2.3.3.2 which yields project runoff using the testing should be implemented as a part of the design rational method that does not result in an increase in process to determine appropriate design considerations for runoff for the 50% annual chance relative to existing your particular location. Design processes for ponds are conditions, then detention for the 50% annual chance is included in Section 6 of this Manual. not required.

18 Section 2 Hydrology 1

If the post project runoff is higher than existing conditions (b) Water imported from any source outside the INTRODUCTION for the 50% annual chance event, and sustainable boundaries of the state for use in the state and drainage measures are designed to the specifications in which is transported through the beds and banks this manual, the following method can be used to decrease of any navigable stream within the state or by 2 the required detention storage computed from the Modified utilizing any facilities owned or operated by the HYDROLOGY Rational Method for the 50% annual chance event: state is the property of the state.”

Figure 2.3 Process for C Value Adjustment The City of Dallas has been granted water rights in the upper Trinity River Basin for municipal, domestic, 3

industrial, mining, agricultural (livestock and irrigation), ROADWAY

Determine preliminar detention volume needed recreation and hydro-electric purposes. Dallas Water DRAINAGE DESIGN using the modiﬁed rational method with no Utilities manages the majority of the City’s water rights. adustments for sustainale drainage measures Texas Water Code Chapter 11 and Texas Administrative Code

Title 30 Chapter 295 and 297 should be thoroughly reviewed 4 to understand the regulatory impacts and permitting BRIDGE

requirements of collecting and retaining storm water. HYDRAULIC DESIGN 2 Design sustainale drainage measure ith ater

ualit volume computed from Euation 22 5 DESIGN OPEN CHANNEL

Sutract the storage volume of the sustainale drainage 6 DRAINAGE

measures from the preliminar detention volume to STORAGE DESIGN determine the adusted detention volume needed

2.3.4 Water Rights 7 CONTROL MEASURES EROSION & SEDIMENT Surface water in Texas is owned by the State and held in trust for the citizens of the State. The State grants the right to use this water to different people and entities such as farmers or ranchers, cities, industries, businesses, and

other public and private interests. 8

The Texas Commission on Environmental Quality (TCEQ) FLOODPLAIN & SUMP is the State Agency responsible for the administration of DESIGN REQUIREMENTS the State’s water rights. Information on water rights can be found on the TCEQ website.

State water may not be impounded and/or diverted 9 without a water right. State water is defined by Texas

Water Code §11.021 as REQUIREMENTS OTHER REGULATORY OTHER REGULATORY

“(a) The water of the ordinary flow, underflow, and tides of every flowing river, natural stream, and

lake, and of every bay or arm of the Gulf of 10

Mexico, and the storm water, floodwater, and SUBMITTAL rainwater of every river, natural stream, canyon, REQUIREMENTS ravine, depression, and watershed in the state is the property of the state. 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 19 APPENDICES

SECTION 3 Roadway Drainage Design

Dallas Drainage Design Manual 21 3.1 3.2 GENERAL IMPROVED ROADWAY Streets or roadways shall be designed to convey the runoff DRAINAGE which results from the 1% annual chance storm event between the curbs, or where no curb exists, within the roadside ditches. Alleys shall be capable of conveying 3.2.1 Street Capacity runoff from the 1% annual chance storm event within the limits of the paved surface. Streets may be used for stormwater drainage only if the calculated stormwater flow does not exceed the maximum Inlets shall be placed at locations where the gutter flow depth as provided in Table 3.1. A Manning's capacity is exceeded by runoff from the 1% annual roughness coefficient of 0.0175 shall be used in calculating chance storm event. Likewise, inlets shall be placed at street flow conditions. Where streets are not capable of locations where alley capacity is exceeded by runoff from carrying their design criteria stormwater discharge, inlets the 1% annual chance storm event. Consideration must or curb openings are required. The inlets or openings will be given to such factors as location relative to streets, discharge into a drainage channel or storm drain system. schools, parks and other areas subject to frequent The following table specifies the allowable encroachment pedestrian use as well as basic economics. A street or limits for the different street types. alley adjacent to an open channel shall have the edge of pavement with a design elevation not lower than the Table 3.1 Encroachment Limits drainage and floodway easement elevation with required minimum freeboard, or as directed by the Director. Street Allowable Encroachment (dry lane) Classification Drainage design requirements for open and closed Minor Arterial Maximum depth of 6" or top of curb systems shall provide protection for property during the and lower 1% annual chance storm event. The design flow will result from assuming fully developed conditions as projected Principal Arterial One lane of traffic in each direction must by the City's current zoning maps, and this projected remain open flow shall be carried in the streets and closed drainage systems in accordance with these guidelines. Runoff All streets shall be capable of conveying the 1% annual from paved areas shall be conveyed through enclosed chance storm event runoff without exceeding the top of storm drain systems if curb and gutter are used. Ditches curb, as shown in Figure 3.1. are allowed subject to the requirements in Section 3.4. Throughout this section, nomographs are provided as design aids for convenience. Designers may use the nomographs, spreadsheet calculations, or software from the approved list on the City of Dallas website or other software approved by the Director.

22 Section 3 Roadway Drainage Design DRAINAGE IMPROVED ROADWAY depressed gutter, refertothecurrentversionofHEC-22. For determiningtheflowcapacity inastreetwith HEC-22, ThirdEdition,2009, Equation4.2and4.3.) for flow intriangularchannels (“Manning'sEquation, This formulaisareformulationofManning'sEquation d =depthofflow(ft) S (a valueofn=0.0175tobeused) n =Roughnesscoefficientforstreetpaving Q =flowrate(cfs) flow inaslopemaybeexpressedasfollows: cross slope.Stormwaterflowsinastreethavingstraight Figure 3.1appliestoallwidthstreetshavingastraight and longitudinalgrades. Street DesignManualforlimitationsonstreetcross-slopes of flowinastreethavingstraightcross-slope.Seethe Equation 3.1maybeusedtodeterminethecapacity 3.2.2 StraightCrownStreet 6 ur5rn Minor Arterial&Lower 6 ur Principal Arterial(Undivided) 6 ur Principal Arterial(Divided) Figure 3.1DryLane(AllowableEncroachment) S L x =crossslope(ft/ft) =longitudinalslope(ft/ft)

= Q rsssle rsssle 0.56 ___ n S

10 Lane

Oen x 100YR SreeFl 1.67

S 210 Lane L 0.5 RO RO RO Oen ( Sree Fl __

S d 100YR x

) 2.67 Sree Fl 10 Lane 100YR Oen (Equation3.1) W P =Wetted perimeter (ft) (a valueofn=0.0175tobeused) n =Roughnesscoefficientforstreetpaving S R =Hydraulicradius(ft) A =Crosssectionalareaofflow(ft Q =Flow(cfs) gutter capacityinstreetswithparaboliccrowns: The followingformulascanbeusedfordeterminingthe 3.2.3 ParabolicCrownStreet for streetsand minimumgradeforvalleygutters. Street DesignManualforlongitudinal gradedesigncriteria section(s) toachievepositive surfacedrainage.Seethe the engineeredcutsandfills, andproposedpavement must considerthecharacteristics oftheunderlyingsoils, within thestreet.Designstreet gradesandcrossslopes toward andintoinletswithoutsagspuddlesalongor cross slopesthatprovideproperflowofsurfacedrainage The designshallachievelongitudinalstreetgradesand 2. 1. street intersectionissubjecttothefollowingcriteria: The useofvalleygutterstoconveystormwateracrossa 3.2.4 ValleyGutterFlow Figure 3.2ParabolicCrownStreetFlowCapacity C f O =Longitudinalslopeofthestreetgutter(ft/ft) O =Crownheightofthestreet(ft) =Widthofthestreet(ft) only thelowerclassifiedstreet. not bepermitted;andparallelvalleyguttersmaycross At anyintersection,perpendicularvalleygutterswill a valleygutter. Principal andminorarterialsshallnot·becrossedby Q = 1.486 A

R = =

A W ______P _ A (R) O 6

(Equation3.3) ⅔ O

n (Equation3.4) W (S

o f

) ½ Dallas DrainageDesign Manual

2 ) (Equation3.2) C o 23

24 Section 3 Roadway Drainage Design Figure 3.4CurbInlet lesser degreethangrateinlets. tend tolosecapacityasstreetgradesincrease,buta amounts ofdebris.Similartograteinlets,curbinletsalso sag locations,andwithflowsthattypicallycarrylarge most effectivetypeofinletonslopesflatterthan3%,in Curb inlets(bothrecessedandnon-recessed)arethe 3.3.1.2 CurbInlet Figure 3.3GrateInlet clogged byfloatingdebrisduring1% satisfactorily inarangeofconditions,theymaybecome Although grateinletsmaybedesignedtooperate 3.3.1.1 GrateInlet Director. use ofothertypesinletsandmustbeapprovedbythe only atlocationswherespacerestrictionsprohibitthe to ADAguidelines.Forthesereasons,theymaybeused chair andbicycletrafficmustbedesignedaccording events. Inaddition,theycanproduceahazardtowheel- Section Grate Inlet H Section Curb OpeningInlet i

H d 2

L θ W W L annual chance a=0.208 h h d o +d y W 0 i -(h/2) y W storm Figure 3.5Y-Inlet Y-inlets aremostoftenusedinswaleandsagdrainage. 3.3.1.3 Y-Inlet Figure 3.6CombinationInlet types ofinletsandmustbeapprovedbytheDirector. locations wherespacerestrictionsprohibittheuseofother guidelines. Forthesereasons,theymaybeusedonlyat and bicycle traffic and must be designed according to ADA a combinationinletcanproducehazardtowheel-chair grate portionoftheinlet.Duetopresencegrate, as a"sweeper",andremovedebrisbeforeitreachesthe on theupstreamsideofcombinationinletitwillact the curbportionofinlet.Ifaopeningisextended reduces thechanceofcloggingbydebriswithflowinto advantages ofbothinlettypes.Thecombinationalso the curbinlet.Thisconfigurationprovidesmanyof A combinationinletconsistsofboththegrateand 3.3.1.4 CombinationInlet Section Combination Inlet Surae Ma aer Section A Y-Inlet Plan A Sle y 6 7 L Sle Sle L Dallas DrainageDesign Manual L y =+a Sle W h A y a h 25

11 10 9 8 7 6 5 4 3 2 1 APPENDICES OPERATION & SUBMITTAL OTHER REGULATORY FLOODPLAIN & SUMP EROSION & SEDIMENT DRAINAGE OPEN CHANNEL BRIDGE ROADWAY HYDROLOGY INTRODUCTION MAINTENANCE REQUIREMENTS REQUIREMENTS DESIGN REQUIREMENTS CONTROL MEASURES STORAGE DESIGN DESIGN HYDRAULIC DESIGN DRAINAGE DESIGN 3.3.1.5 Slotted Drain Inlet 9. The end of the recessed inlet box shall be at least 10 feet from a curb return or driveway wing; and the inlet Slotted drain inlets can be used to intercept sheet flow, or shall be located to minimize interference with the use flow in wide sections. They are not recommended for use of adjacent property. Inlets shall not be located across in the City of Dallas since they are susceptible to clogging from median openings where a drive may be added. from debris. Use of slotted inlets may not be used unless 10. Inlets located directly above storm drain lines approved by the Director. shall be avoided. Figure 3.7 Slotted Drain Inlet 11. Data shown at each inlet shall include paving or storm drain stationing at centerline of inlet, size of inlet, type W of inlet, top-of-curb elevation and flow line of inlet. 12. Inlet box depth shall not be less than 4 feet when the lateral is 21 inches. 13. Laterals conveying flow from an inlet must tie into a trunk line and shall not tie into another inlet, unless otherwise approved by the Director. 14. Grate type inlets shall be carefully considered and used only if justified due to site conditions. Grate 3.3.2 Inlet Design Requirements inlets must be approved by the Director. In situations where only the lower portion of an enclosed Inlets shall be placed to ensure that the flow in the 1% annual storm drain system is being built, stub-outs for future chance storm event in a street does not exceed top-of-curb connections must be included. In this case, it is not elevation, and that encroachment into the travel way does necessary to capture all the street flow at the stub-out. At not violate the minimum dry lane requirements of 10’ of a minimum, there must be enough inlets to capture an pavement available to drive on, in each direction during 1% amount equal to the total street flow capacity at the stub-out. annual chance storm events. Inlets shall be appropriately placed to avoid excessive If in the judgment of the engineer the flow in the gutter water draining through an intersection. Inlets shall be is excessive, the storm drain shall be extended to a point provided on all streets intersecting minor and principal where the gutter flow can be effectively intercepted by arterials to capture the surface drainage in the street with inlets. Guidelines for inlet placement include: no drainage bypass. A few considerations for designing 1. Placing multiple curb inlets at a single location is only drainage in conjunction with the new paving construction permitted in areas with steep grades (4% or greater) or reconstruction projects are listed below: to prevent flooding and avoid exceeding street -- Inlets shall not be placed at inconvenient locations for capacity in flatter reaches downstream. property owners such as near driveways and lead walks. 2. For all sag locations on a principal arterial street, -- Grate inlets may be used only where space restrictions flanking on-grade inlets shall be placed not more than prohibit the use of other types of inlets. If used, the 50 feet away on each side of the sag inlet. inlet opening should be designed to be twice as large 3. To minimize water draining through an intersection, as the theoretical required area to compensate for inlets shall be placed upstream from an intersection. clogging and must be approved by the Director. 4. Inlets shall also be located in alleys upstream of an -- Combination curb inlets (with opening in curb and intersection and where necessary to prevent water grate opening in gutter) may be used only where space from entering intersections in amounts exceeding behind the curb prohibits the use of other inlet types. allowed street capacity. -- Where recessed inlets are required, they shall not 5. Inlets shall be placed upstream from right angle turns. decrease the width of sidewalk or interfere with utilities. 6. Inlet boxes designed more than 4.5 feet deep require -- Recessed inlets must also be depressed, unless otherwise a special detail. approved by the Director. Maximum allowable gutter depression for recessed inlets shall be seven inches. 7. All Y-inlets and inlets 10-foot or greater shall have a minimum 21-inch reinforced concrete pipe (RCP) lateral. -- Recessed inlets may be used on divided thoroughfares. 8. Inlets are required at all sag points. -- Non-recessed, depressed inlets shall have a maximum allowable gutter depression of five inches. 26 Section 3 Roadway Drainage Design grate inletareL of fiftypercent,theeffective lengthandwidthofasingle width ofW = 1.3 ft.Therefore,applyingacloggingfactor standards hasanactuallengthofL=2.6ftand of fiftypercent(C = 0.50).Asinglegrateinletper251D and widthofthegrateopeningarereducedbyafactor of cloggingagratedinletongrade,theactuallength width ofanybarsorvanes.To accountfortheeffects opening istheoveralldimensionofgrateless The actuallength(L discussed inrelationtocurbopeninginletsongrade. of grateinlets,whichisanalogoustothebypassflow grate. Bothofthesephenomenacontributetoflowbypass approaching flowistoohigh,thewill“splashover” will beinterceptedbytheinlet.Whenvelocityof little oftheapproachingflowthatexceedsgratewidth width oftheapproachingflowexceedsgratewidth,very intercept alloftheapproachingflow. Incaseswherethe not exceedthegratewidth,inletmightbeableto approaching flowvelocityisslowandthewidthdoes velocity oftheflowapproachinggrate.When on thewidthandlengthofgrate The interceptioncapacityofgrateinletsongradedepends Grate InletonGrade 3.3.3.1 GrateInlet inlet capacities. spreadsheet templatethatmaybeutilizedforcomputing of Dallaswebsite.AppendixA.3providesanapproved from anapprovedlistwhichcanbefoundontheCity sections, ortheymaybeperformedusingsoftware computed fromtheequationsprovidedinfollowing of thecurbopening.Inletcapacitycalculationsmaybe depth atthecurbopeningandheightlength etc. Thecapacityofaninletinsagdependsonthewater on streetgrade,deflections,crossslope,depressions, inlets insag.Thecapacityofanongradeinletdepends Inlet capacitiesforongradeinletsarelessthanthoseof guidelines arebasedoninletsgradeandatsagpoints. The followinginletcapacityformulasanddesign system conveyance. they draintoandfrom,otherconnecteddrainage design criteriaoftheroadwaystheyservice,ponds Inlets andopeningswillbelocatedsizedtomeetthe 3.3.3 InletCapacityCalculations the CityofDallasandtypicallocationsforeach. Refer toFigure3.8forstandardstormdraininletsusedin grated inletongradeisasfollows: The proceduretodetermine theinterceptioncapacityofa E = 1.3 ft andW A ) andwidth(W E = 0.7 ft, respectively. A ) ofthegrate (Q Step 3.Determinetheamountofsideflow S V =Velocity offlowapproachinginlet(ft/s) L Q T =Total spreadofwaterintheroadway(ft) V V =Velocity offlowapproachinginlet(ft/s) grated inlet(cfs) (an effectivewidthW into frontaldischarge(Q Q Q Q Q amount of frontal discharge intercepted by the grate. amount offrontaldischargeinterceptedbythegrate. velocity exceedsthesplash-overvelocity, calculatethe of theapproachingfrontaldischarge.Whenapproach over velocity, itcanbeassumedthatthegrateinterceptsall 2.0 ft/s.Whentheapproachvelocityislessthansplash- velocity. Thesplash-overvelocityforasinglegrateinletis Step 2.Comparetheapproachvelocitytosplash-over W Q inlet (cfs) beyond thewidthofgrate). Step 1.Dividetheflowapproachinginlet(Q Q grate (cfs) Q Q X E O SIDE S APPROACH W W INTERCEPT,FRONT INTERCEPT, SIDE E INTERCEPT, SIDE

INTERCEPT, SIDE =Sidedischarge(cfs) =Splash-overvelocity(V = =Effectivewidthofgrate(ft) = W =Portionofapproachingflowwithinthewidth =Frontalflowapproachinggratedinlet(cfs) Street cross slope (not longitudinal slope of gutter) (ft/ft) Streetcrossslope(notlongitudinal slopeofgutter)(ft/ft) Effectivelengthofgrate(ft). lengthofL

Q =Sideflow(i.e.,outside widthofgrate)(cfs) Q = Q INTERCEPT,FRONT S Q = =Total flowapproachingthegrate(cfs) APPROACH = APPROACH

= ) thatisinterceptedbythegrate. =Frontaldischargeinterceptedby Sidedischargeinterceptedbygrated [ 1 + ______ E (Equation 3.8) =0.7ft) [ = 1 - W ( - ) andsideflow(Q

( Q ( S ___ 0.15V O Q 1.0 W SIDE ______X T =2.0ft/s) W E L

(Equation3.7)

) - E Dallas DrainageDesign Manual 2.67 2.3 (V 0.09 1.8 ]

)

]

(Equation 3.6) (Equation3.9)

- S ), (i.e.,flow V 0 APPROACH ) ) Q E

= W 1.3 ft 1.3 ft

) 27

Common Inlet Description Where Used Inlet size

5 All Minr Srees 10 Sanar ur ening inle n 14 grae

5 All Minr Srees 10 Sanar ur ening inle a 14 l in

5 All Diie Senar an Mar 10 Srees Reesse ur ening inle n 14 grae

5 All Diie Senar an Mar 10 Srees Reesse ur ening inle a 14 l in

Cinain inles e use nl Single ere sae ein ur riis Dule er inle es an in alles an Grae inle ur e Trile i erissin e Direr n Grae

Single D n use ee i erissin Dule e Direr Grae inle ur e Trile a l in Seial 2 Grae 4 Grae Inle lain i n ur 6 Grae Alles Drieas i erissin Grae inles 8 Grae e Direr Guer e

Y Oen Cannels Dies Yinle

28 Section 3 Roadway Drainage Design Figure 3.9. C (C operating asaweir, acloggingfactoroffiftypercent To d =Flowdepthapproachinginlet(ft) P Figure 3.9GratePerimeter P C Q =Inletcapacityofthegratedinlet(ft/s) curb, disregardthelengthofgrateagainstcurb. perimeter ofthegrate.Whengrateislocatednexttoa a weir, usingtheweirequationwithalengthequivalentto Step 1.Calculatethecapacityofagrateinletoperatingas capacity equaltothesmalleroftworesults. flow andorificeconditions,thenadoptadesign shall estimatethecapacityofinletunderbothweir such asgratesizeandbarconfiguration.Thedesigner transition fromweirflowtoorificedependsonfactors shallower depths,andasanorificeatlargerdepths.The A grateinletinasaglocationoperatesasweirat calculations downstream. flow totheroadwaycalculationsandinletcapacity the inletandbypassflow, andapplythe bypass Step 4.Calculatetheamountofflowinterceptedby grate typesandconfigurations. Design Manual(HEC-22)providesguidanceforother The FederalHighwayAdministration’s UrbanDrainage P perimeter ofthegrate(P): Grate InletonSag A Q E E L W =Actualperimeterofthegrate(ft)asshownin accountfortheeffectsofcloggingagratedinlet L =Effectivegrateperimeterlength(ft) =Effectivegrateperimeterlength(ft) =Cloggingfactor(C BYPASS =Weir coefficient(C = 0.50) shallbeappliedtotheactual(unclogged) P Q = Q P A =WL -area ofars P E A A =2(W+L -ars)(without cur) =2(W- widthofars)+ L (with cur) C = (1 = APPROACH W C - P L E L + P ) d Cur W = 0.50) =3.0forU.S.Traditional Units) L

Q 1.5 A INTERCEPT

(Equation3.12) (Equation 3.11) W Euto 3.10) (Equation Step 3.Usemoreconservativeofthetworesults clear openingofthegratereducedbyacloggingfactor as anorifice.Usetheorificeequationassuming L g =Gravitationalacceleration(32.2ft/s C Q =Inletcapacityofthegratedinlet(cfs) H Q =Gutterflow(cfs) L =Lengthofinletrequiredtointerceptthegutterflow(ft) be calculatedusingEquation3.15. The lengthofinletnecessarytointerceptgutterflowcan Recessed andStandardCurbOpeningInletsonGrade 3.3.3.2 CurbInlet C Step 2. C d =Flowdepthaboveinlet(ft) A y =Depthofflowinapproach gutter a =Gutterdepression Q required inletlengthcomputedfromEquation3.15. flow interceptedbyaninletlengththatislessthanthe Figure 3.10canbeusedtodeterminetheamountof H the inletdepression(ft) provides guidanceforothergratetypesandconfigurations. Administration’s UrbanDrainageDesignManual(HEC-22) single grateinletper251DstandardsisA less theareaofbarsorvanes).Theactualopeningfora A actual clearopeningof A A

E O A i 2 1 = =Areacloggingfactor(C =FlowinterceptedbyinletoflengthL =Lengthofcurbopeningfor 100% interception =Effective(clogged)gratearea(ft =Inletdepression(ft) =Depthofflowinthegutterapproachinginletplus = 0.50. Asinglegrateinletper251Dstandardshasan

= Actual opening area of the grate inlet (i.e., the total area Actualopeningareaofthegrateinlet(i.e.,total Orificecoefficient(C L Q Calculatethecapacityofagrateinletoperating = = A C = E

(1 = 0.70(H ______0 Q(H A C - E 1 2gd) ( 1 -H 2.5 A A ) =1.5ft - H O A 2 = ) A 0.67forU.S.Traditional Units) 2

(Equation3.14) 1/2 2.5 = 0.50)

(Equation3.13) ) 2 Dallas DrainageDesign Manual (Equation3.15) . TheFederalHighway 2 ) 2

= ) 1.5ft 2 . 29

Sag inlets operate as a weir up to a depth equal to Figure 3.11 Y-Inlet Capacity Curves at Sag Point 1.4 times the height of opening, and as an orifice for 25 greater depths. See Figure 3.4 for dimensions. The corresponding equations for weir flow are: 20 44 Q = 2.1 (L + 1.8W ) d1.5 (Equation 3.16) 15 Q = inlet capture (cfs)

yo = 0.2 W = width of depression (ft) (measured transversely from yo = 0.3 face inlet) 10 yo = 0.4 9 yo = 0.5

- Length of Inlet Opening (ft) yo = 0.6 L = length of curb opening, (ft) i yo = 0.7 L 8 yo = 0.8 yo = 0.9 d = depth of water at curb (ft) (from the normal cross 22 7 yo = 1.0 slope gutter flow line) 6 Orifice Flow 5 Q = 0.60 hL (2g(d - _h )) 0.5 (Equation 3.17) 4 i 2 1 2 4 5 6 7 8 910 15 20 0 40 h = height of inlet opening (ft) Q - Flow Rate to Inlet (CFS) (see(see enlarged enlarged figure ﬁgure in inAppendix Appendix A.7) A.7) L = length of curb opening (ft)

depth at lip of curb opening (ft) di = h = height of curb opening orifice (ft)

30 Section 3 Roadway Drainage Design C to theactual(unclogged)lengthofaslottedinlet(L): L As withgrateinlets,acloggingfactor(C design capacityequaltothesmalleroftworesults. both weirflowandorificeconditions,thenadopta designer shallestimatethecapacityofinletunder either asaweiroranorifice.Aswithgratedinlets,the When locatedinasump,slotteddraininletscanfunction than 1.75inches. for curbopeninginletswhentheslotopeningsaregreater Therefore, thedesignermayuseequationsdeveloped when theslotopeningsaregreaterthan1.75inches. closely tothehydrauliccapacityofcurb-openinginlets the hydrauliccapacityofslotteddraininletscorresponds Federal HighwayAdministration(FHWA) suggeststhat function asaside-flowweir, muchlikecurb-openinginlets. approval. Whenlocatedonagrade,slotteddraininlets Slotted draininletsshallonlybespecifiedwithpriorCity 3.3.3.5 SlottedDrainInlet See AppendixA.3forSagInletDesignWorksheet. 3. 2. 1. the gratedinlet. assumes thatthecurbopeninginletisplacedupstreamof combination ofacurbopeninginletandgrate The procedureforcalculatingthecapacityofa 3.3.3.4 CombinationInlet L =Actual(unclogged)lengthoftheslottedinlet(ft) E L =Effectivegrateperimeterlength(ft) =Cloggingfactor(C by thegratedinlet. Determine theportionofbypassedflowintercepted on grade). that bypassesthecurbopeningpartofinlet(if Determine thedepth,width,andvelocityofflow curb-opening partoftheinlet. Determine theportionofflowinterceptedby L E = (1 C - L L =0.50) ) L (Equation3.18) L ) shallbeapplied provide theexceptioninwriting. the needforanexception,discusswithDirectorand of 2ft/satdesigndischarge.Ifprojectconstraintsdictate Bar ditchesshallbedesignedtohaveaminimumvelocity 3:1 withabottomwidthdependentonrequiredcapacity. gutter. Barditchesshouldhaveamaximumsideslopeof Bar ditchescanbeusedonroadswithoutcurband 3.4.1 BarDitchDesign ROADWAY DRAINAGE UNIMPROVED 3.4 additional treatment. Check damscan beusedtoslowvelocities andprovide approved byDirector, withaminimumbottomwidthof2feet. Bioswales shouldhavesideslopes 3:1orless,unless design flowrate,shouldgenerally bebelow4inches. time of5minutesatdesign flow rate. Water depth,at Design shouldallowforaminimumhydraulicretention Design Considerations minimum of3feetfrompropertylines. The topofthesideslopebioswalesshallbesetback a Site Considerations but theycanremovesedimentandimprovewaterquality. provide thesamepollutantremovalcapacityasbioretention, contain bioretentionsoilmixorengineeredmedia,sodonot to filterandconveystormwaterrunoff.Bioswalesdonot Bioswales aregrassorvegetatedchannelsthatdesigned 3.4.2.1 Bioswales 3.4.2 Bioswales zones. the StreetDesignManualforminimumpedestrianclear design requirementsdiscussedinSection3.2.1.Referto chance stormeventwithintheright-of-wayandmeet Bar ditchesshallbedesignedtocontainthe1%annual / Bioretention Swales Dallas DrainageDesign Manual 31

At the inlet and outlet of the bioswale, vegetation that can Bioretention swales should have a maximum ponding withstand high velocities should be chosen. drawdown time of 24 hours for the design flow. A longer ponding time may be approved by the Director. If not, an See Appendix A.6 for landscaping requirements. underdrain system should be used. See Section 6.10 for infiltration requirements. Sizing Longitudinal slopes should not exceed 4%. If channel Bioswales are designed for conveyance rather than slopes are above 2%, drop structures or check dams storage. Using site conditions and design requirements should be used. A minimum design head of 3 to 5 feet above, open channel flow methods (see Section 5) can from inflow to outflow is needed for positive drainage. be used for design. When not used for primary roadway drainage, design is required to convey 1% annual chance A gravel reservoir course can be provided under the event discharge. bioretention soil mix for additional storage. A geotextile liner should be used to separate filter media and native soil. 3.4.2.2 Bioretention Swales Bioretention swales should have a minimum bottom Bioretention swales are typically a linear channel with a width of 2 feet and a recommended side slope of 4:1. parabolic or trapezoidal cross-section and may have a Bioretention swales should have a maximum side slope sloped bottom. They contain a filter bed of bioretention of 3:1 but can be steeper if located in a median and soil mix or engineered media and an underdrain system approved by the Director. Overflow ponding depth should and are typically used along roadways and in parking lot be 6-12 inches. At the downstream end of the channel, islands. Bioretention swales can be effective for treating the ponding depth should not exceed 18 inches. runoff, reducing sediment, and routing runoff to surface waters or storm drain systems. They can be used for Energy dissipators may be needed for concentrated inflows. retrofits, especially for existing ditch and swale systems. Overflow can be provided by adjacent inlets, vertical stand They can also be used within medians between curbs if pipes, horizontal drainage pipes, or armored channels at the space is available. Bioretention swales can be planted maximum ponding elevations which lead to surface waters, with grass but are more effective at improving water public storm drain systems, or storage reservoirs. Backwater quality and slowing runoff velocities when vegetated calculations may be required depending on the capacity of with seeds or other plant material. A drain or overflow the discharge system during large storm events. The overflow structure is typically located at one end. Check dams or shall be sized for the 1% annual chance 24-hr storm event. other methods are typically employed to slow runoff and promote infiltration and treatment. If an underdrain is installed, the gravel backfill shall have a minimum depth of 26 inches with a porosity of 0.35. Site Considerations Bioretention swales should have a maximum contributing Aesthetics should be taken into consideration when the drainage area of 5 acres. swale is placed in a public area.

Bioretention swales are not permitted in areas where there Sizing is seasonal high groundwater present less than 4 feet in Bioretention swales can be sized similarly to rain gardens depth from the bottom of the swale or where infiltration or bioretention areas (See Sections 6.8 and 6.9). See would contribute to soil or groundwater contamination. Section 2.3.3 for C value adjustments. The cross-section of the bioretention swale typically does not allow for erosive velocities. 3.4.3 Culvert Crossing The top of the side slope of bioretention swales should Refer to Section 3.7 for culvert hydraulic design. Safety end be located a minimum of 3 feet away from buildings and treatments may be necessary for culverts under unimproved property lines. If located within 10 feet of a building, a roadways as the culvert opening may constitute a safety liner must be used. hazard to the traveling public. TxDOT provides guidance on the use of guardrail or safety end treatments for culverts Design Considerations located within a defined “clear zone” adjacent to a roadway. Bioretention swales must be able to accomodate the Refer to the TxDOT Roadway Design Manual for guidance 1% annual chance storm event through capture or flow on determining whether guardrail or a safety end treatment may be needed for a culvert under an unimproved roadway. 32 Section 3 Roadway Drainage Design not betieddirectlyintothebackofstorminlets. roof draindownspoutsorprivatefoundationdrainsshould Auxiliary drainagecomingfromoff-sitesourcessuchas with designwatersurface,andhydrauliccomputations. and inotherapplicablelocations,providesection,profile and drainageditches.Forditchesalongroads,railroads, and Y-inlets (dropinlets)aretobeusedinunpavedareas In general,curbinletsaretobeusedalongpavedstreets 3 feet offofthepavementcurbline.SeeFigure3.12. zone ofthestreetbetweenbackcurbandaplane major stormdrainagefacilitiesnormallyareplacedinthe over stormdrainagepipes.Stormmainsand In practice,muchgreaterdepthsaregenerallyutilized construction process. subgrade inalllocationstoavoiddamageduringthe minimum of6inchesbelowthebottompaving Generally, thetopofalldrainagepipesshouldbea pavement warpdownareatotheinletthroat. is requiredforstormdrainagelateralsclosetoinletsinthe the pavementsubgradepreparationzone.Specialcaution The topofstormdrainageconduitsmustnotconflictwith Infrastructure Requirements 3.5.1 UtilityandDrainage CONSIDERATIONS ROADWAY DRAINAGE ADDITIONAL 3.5 A S Figure 3.12UtilityinTypical Streets Tele Eleri & CAT aries 65115 Tele Eleri & CAT 25 Sr 112 DiieArerialSrees Drain Sr Drain Sr DrainInle 27 LalSrees &Sree Ligs RO 5010 aseaer aseaer RO 15 15 10 Dallas DrainageDesign Manual Faili Mar aer Gas &T 65115 25 & Gas aries aer 33

34 Section 3 Roadway Drainage Design V n =Porosity(gforgravel,pconcreteorasphalt) d =Depth(ft)(gforgravel,pconcreteorasphalt) which fallsonthesurfacepermeablepavementarea. The totalvolumetobeinfiltratedshouldonlyincluderainfall design waterqualityvolumeandotherparameters. used todeterminethedepthofgravellayerbasedona to haveaporosityof0.32.Thefollowingequationcanbe porosity of0.18.Thegravelbasecourseshouldbeassumed Pervious concreteandasphaltcanbeassumedtohavea See Section2.3.3forCvalueadjustments. which fallsonitandnotrunoffroutedfromotherareas. of area,astheyaredesignedtotreatonlytheprecipitation Pervious pavementareascanbeinstalledforanyamount Sizing for maintenance. A minimumwidthof8feetaccessshouldbeprovided of 20percenttotalvoidvolumeaftercompaction. pavement. Thereservoircourseshouldhaveaminimum should beaminimumof6-18inchesforpervious with littleornofines.Reservoircourseaggregatedepth The reservoircoursemustconsistofsinglesizeaggregate Sealant shouldnotbeusedontopofpermeablepaving. the materialshouldbenogreaterthan0.30. Pervious pavementshouldbe4-6inchesthick.Porosityof Design Considerations conventional mixcanbeusedifpatchingisrequired. in porousasphaltduetoenhanceddrainage,but asphalt. Potholesandcrackingarelesslikelytooccur 18‑36 in, thatwillnotallowwatertorisethroughthe system mustbedesignedwithabasedepth,typically Porous asphaltisdesignedtobeADAcompliant.The sediment andpollutantloading. (more than25,000vehicles/day)orforareaswithhigh Porous asphaltisnotsuitableforroadswithheavytraffic for parkinglots,walkingpaths,sidewalks,plazas,etc. pavement andunderlyingbase.Porousasphaltissuitable 24-48 hours. Check thatdrain timeofthetotalponding depthiswithin T =Filltime(hrs) k =Percolation(in/hr) A =Surfacearea(ft WQ

g = Designwaterqualityvolume(ft = __ n 1 g

[(

V ___ A WQ 2

) ) - 12 __ kT -

n p d p ] 3 (Equation3.19) ) (SeeSection2.3.3) water andenableinfiltrationtotheunderlyingsubbasesoils. of 9-18inches.Thespacesbetweentheaggregatesstore aggregates. Thesystemmustbedesignedwithabasedepth consisting ofopen-gradedbeddingbase,andsubbase surface runofftoflowintoahighlypermeablereservoirarea natural colors,andfiredfinishes.Bothallow100%of similarly consistofbrickunitsinaninterlockingpattern, finishes withsmall,stonefilledjoints.Permeablebrickpavers units inavarietyofinterlockingpatterns,shapes,colors,and Permeable interlockingconcretepaversconsistof Permeable Pavers-InterlockingConcreteorBrick areas withhighsedimentandpollutantloading. with heavytraffic(morethan25,000vehicles/day)orfor plazas, andlowtrafficroads,isnotsuitableforroads parking areas,walkingpaths,sidewalks,driveways, Permeable unitpavingissuitableforparkinglots,street system orcollectedforreuse. filtration forthestormwaterbeforeenteringstormsewer through. Thesystemreducesimperviousareaandprovides be filledwithaggregatethatstormwaterrunoffcanfilter are designedwithvoidspacesinbetweenthemthatcan or openjointedandcellpavingblocks.Theunits concrete pavement,permeableinterlockingbrickpavers, Permeable unitpavingconsistsofpermeableinterlocking 3.5.2.3 PermeableUnitPavementSystem Figure 3.13PermeableUnitPavementSystem interlocking paversaredesignedtobeADAcompliant. street parkingareas,andlow-trafficroads.Permeable walking paths,pedestrianplazas,parkinglots,driveways, Permeable interlockingpaversaresuitableforsidewalks, Dallas DrainageDesign Manual Sugrae Sil Gesnei Unerrain Suase Reserir OenGrae Base Resrir OenGrae Pereale ins Cnree Paers Cnree Cur Curese Being OenGrae 35

36 Section 3 Roadway Drainage Design Organic filters have two different configurations, a compost Organic filters havetwodifferentconfigurations, acompost pollutant removalaswellprevent cloggingofthefiltermedia. continuous. Grasscovercanprovide additionalbacteriaand Filters shouldbedesignedfor intermittent flowratherthan Filters mustbeabletopassthe1% Design Considerations buildings androadways10feetfrompropertylines. Filters shouldbesetbackaminimumof5feetfrom not belocatedinanareawithaslopegreaterthan6% require considerationofanunderdrainsystem.Filtersshould with highsedimentloadings.Areasclaysoilsmay loadings. However, sandfiltersshouldnotbeusedforrunoff media filterscanbeusedinareaswithhigherpollutant drainage areanogreaterthan10acres.Sandororganic Sand ororganicmediafiltersshouldhaveacontributing Figure 3.14Sand&OrganicMediaFilters Underground filterscanbeusedinspace-limitedareas. media bedforfiltration,andunderdraincollectionsystem. Sand ororganicmediafiltersutilizeasedimentationbasin, within runofffromroadwayandparkingsurfaces. and canincludetheremovalofheavymetalsoftenfound These materialsprovideenhancedremovalofpollutants compost, orpeat/sandmixturethatservesasafiltermedia. Sand andorganicmediafilterscontaineithersand,leaf 3.5.3 SandandOrganicMediaFilters 10%, and50% installed. Velocities shallbecheckedforthe1%,2%, will causewashout,abypassoroverflowrisershouldbe event throughcaptureorflowdiversion.Iflargeevents Inﬂow Seienain Prereaen annual chance Basin Filer Be stormevents. Unerrain Cllein Sse annual chance Outﬂow storm . V h (use 3.5 ft/dayforsand) k =Coefficientofpermeabilityfiltermedia(ft/day) d t media replacement. Maintenance accessmustbeprovidedforinspectionand downstream structures. overflow, andoverflowshouldberoutedawayfrom erosive. Anemergencyspillwayisneededtoconvey sand filters.Inflowandoutflowvelocitiesshouldnotbe Energy dissipatorsshouldbeusedattheinletsofsurface Gravel shouldhaveavoidspaceofapproximately40%. layer. Theunderdrainmusthaveaminimumslopeof1%. underdrain belowandfilterfabricplacedbetweeneach with 3inchesoftopsoilaboveandperforatedpipe (maximum of24inches)sandand/ororganicmedia The mediabedshouldhaveadepthof18inches of 3.5ft/dayshouldbeusedforsand. shall haveaheadof2-6feet.Acoefficientpermeability Organic filtersshallhaveaheadof5-8feet.Sand underlying soil. concrete canbeusedtoseparatethefilterbedfrom Filter bedsshoulddrainwithin40hours.Apolylineror outlet locationsshouldbeplacedtoavoidshort-circuiting. a recommendedlength-to-widthratioof2:1.Inletand hold atleast25%ofthedesignvolumesystemwith The pretreatmentsedimentationbasinshouldbesizedto contain ahighpercentageofdecomposablematerial. sand layer. Ifpeatisusedinthefiltermedia,itshouldnot filter usesalayerof50/50peat/sandmixover6-inch of compostthatisusedasthefiltermedia.Apeat/sand filter orapeat/sandfilter. Acompostfilterhas18inches A basin chamberbasedonadesignwaterqualityvolume: The followingequationcanbeusedtosizethefiltration Sizing length-to-width ratioof2:1. least 25%ofthedesignwater qualityvolumeandhavea sedimentation chamber, which shouldbesizedtoholdat The followingequationcan be usedtosizethe f =Designfilterbeddraintime (days) f f A WQ f =Average heightofwaterabovefilterbed(ft)(1/2h =Filterbeddepth(ft) =Surfaceareaoffilterbed(ft f =

= Designwaterqualityvolume(ft V WQ d * f / [ k * ( h f + d f t )* 2 Dallas DrainageDesign Manual ) f ] 3 (Equation3.21) ) (SeeSection2.3.3) max 37 )

E = Trap efficiency sized to release Vs within 24 hours with an average release rate of 0.5 Hs. The following assumptions can be made:

-- 90% sediment trap efficiency E( = 0.9)

-- Particle settling velocity, W = 0.0033 ft/s for imperviousness < 75%

-- Particle settling velocity, W = 0.0004 ft/s for imperviousness ≥ 75%

-- Average of 24 hour holding period

Using these assumptions,

As = 0.066 * VWQ for I < 75% (Equation 3.23)

As = 0.0081 * VWQ for I ≥ 75 % (Equation 3.24) I = Imperviousness

Using the following equations, compute the minimum storage volume in the facility.

Vmin= 0.75 * VWQ= Vs + Vf + Vf-temp (Equation 3.25)

Vf = Af * df * n (Equation 3.26)

Vf-temp = 2 * hf * Af (Equation 3.27)

Vs = Vmin - Vf - Vf-temp (Equation 3.28) Minimum storage volume in the facility (ft3) Vmin = Design water quality volume (ft3) VWQ = Water volume within filter bed/gravel/pipe (ft3) Vf = Temporary storage volume above filter bed (ft3) Vf-temp = Volume within sediment chamber (ft3) Vs = n = Porosity (0.4)

Bottom surface area of filter bed (ft2) Af = Filter bed depth (ft) df = Average height of water above filter bed (ft) (1/2 ) hf = Hmax

38 Section 3 Roadway Drainage Design within the improved subgrade of a proposed pavement. within theimprovedsubgrade ofaproposedpavement. trees. Nopartoftheproposed stormdrainistobedesigned will notundermineexistingsurface structures,utilitiesor systems arenormallyaligned sothatthenecessarytrenching existing easementsandright-of-wayareas.Stormdrainage Alignments ofproposedstormdrainsystemsshallutilize main lines,andatabruptchangesinalignmentorgrade. Junction boxesshouldbelocatedatjunctionswithstormdrain underground stormsewersforinspectionandcleanout. Storm drainjunctionboxesareneededforaccessto from theDirector. sections. Othertypesofpipeswillneedpriorapproval concrete pipe(RCP)orreinforcedbox(RCB) Enclosed stormdrainsystemsshallbereinforced Manning's equation. using thedesignflow, appropriatepipesize,and The hydraulicgradientandvelocityshallbecalculated P =wettedperimeter(ft) S the wettedperimeter(P) R =hydraulicradius(ft),theareaofflow(A)dividedby n =roughnesscoefficientoftheconduit A =crosssectionalareaoftheconduit(ft Q =flow(cfs) hydraulically designedusingManning'sequation: storm aredetermined.Allenclosedsystemsshallbe size andgradientofpiperequiredtocarrythedesign design stormrunoffquantityenteringeachinlet,the After completingthehydrologiccomputationsof DRAIN SYSTEMDESIGN ENCLOSED STORM 3.6 f =slopeoftheenergygradient(ft/ft) Q = 1.49

______A R 2/3 n

1/2 (Equation3.30)

2 ) curb, atanypointalongtheconduit. The EGLshouldnotbeabovethefinishedgrade,ortopof HGL. TheEGLisalwaysincreasingintheupstreamconduit. pressure head. The EGL is a velocity head (V This totalenergyincludeselevationhead,velocityand energy alongtheopenchannelorconduitcarryingwater. The EGLisanimaginarylinethatthemeasureoftotal tube atanypointalongtheconduit. the levelofwatersurfacethatwouldrisewithinavertical flow. Foraconduitwithpressureflow, theHGLwouldbe open channelorthewatersurfaceofaconduitwithpartial The Hydraulicgradeline(HGL)isthewatersurfaceofan Elevation 3.6.1 StartingHydraulicGradeline applications canbefoundontheCityofDallaswebsite. utilized fordesignofstormsewersinlieuspreadsheet used fordesign.Alistofapprovedsoftwarethatmaybe Storm drainlinecalculationsspreadsheetsmaybe and velocityshallbecalculated atnormaldepth,neglecting which resultsinpartialflow. Insuchcases,thepipecapacity system, theinsidetopof pipe maybeabovetheHGL, In somesituations,generally at theupstreamendofapipe line. channels, thewatersurfaceitselfishydraulicgrade calculations beginattheoutfallofsystem.Inopen The CityofDallasrequiresthatallhydraulicgradient Figure 3.15HydraulicGradient Hrauli GraeLine Free aer Surae Hrauli GraeLine T Pie T Pie a. OpenChannelFlow V b. PressureFlow

2 /2g V Energ GraeLine Dallas DrainageDesign Manual

2 Iner Iner /2g Energ GraeLine 2 /2g) above the 39

Table 3.3 can be used to establish appropriate design tailwater elevations for storm drainage systems based on the expected coincident storm frequency on the outfall channel and the ratio of the drainage area of the storm 60 drain system and the receiving stream.

Table 3.3 Frequencies for Coincidental Occurrences Qi,Vi Qo,Vo

Area Ratio Storm Drain Frequency (Receiving Stream Area/Storm 50% 10% 1% Drain Area) 8. To prevent sedimentation in enclosed systems, Annual Annual Annual minimum flow velocities with full pipe flow shall be Chance Chance Chance 3 ft/s. Higher flow velocities may be associated with 10,000:1 1 1 2 lower flow rates as may be the case with relatively 1,000:1 1 2 10 steep pipes and low tailwater conditions. In such cases, full pipe flow velocities lower than 3 ft/s may 100:1 2 5 25 be allowable as determined by the Director. 10:1 2 10 50 9. Where velocity exceeds 12 ft/s, a special lined RCP 1:1 2 10 100 with a minimum of 1-1/2inch steel clearance on the inside surface shall be used. Maximum velocity in special lined RCP shall be 30 ft/s. Velocity rings 3.6.2 Storm Drain Line Design shall be provided where grade of pipe exceeds 40% and length of pipe exceeds 100 feet. Velocity rings The following guidelines shall be followed for storm shall be cast-in-place type, not metal band type, and drainage design: provide a low pass through notch. 1. The minimum lateral storm drain pipe diameter shall 10. Concrete pipe collars or manufactured transition be 21 inches. pieces must be used at all pipe size changes on trunk 2. Pipe diameters shall increase downstream, unless lines and where the slope difference for the vertical approved by the Director. grade change is less than 3%. Where the algebraic difference for vertical grade is greater than 3%, a 3. At points of change in storm drain size, pipe crowns manhole shall be provided. shall be set at the same elevation. In addition to the criteria listed above, the following 4. A minimum grade of 0.3 percent will be maintained general design guidelines will tend to alleviate or eliminate in the pipe unless approved by the Director. common problems of storm drain performance: 5. Only standard pipe sizes will be used unless approved 1. Select pipe size and slope so that the velocity of flow by the Director. will increase progressively down the system or at least 6. Laterals shall be connected to trunk lines using will not appreciably decrease at inlets, bends or other manholes or reinforced concrete wye connections. changes in geometry or configuration. Special situations may require laterals to be connected 2. For all pipe junctions other than manholes and junction to trunk lines by a cut-in (punch-in). However, such boxes, the angle of intersection shall be 60 degrees or cut-ins must be approved by the Director. as otherwise approved by the Director. 7. Vertical curves in the storm pipe will not be permitted. 3. Inlet laterals will normally connect only one inlet Horizontal curve design for storm drains shall take to the trunk line. Special circumstances requiring into account joint closure. Half tongue exposure is the multiple inlets to be connected with a single lateral maximum opening permitted with tongue and groove shall require the Director's approval. pipe and horizontal curves must meet manufacturer's 4. Storm drain pipes shall be reinforced concrete pipe, requirements for offsetting of the joints. Where minimum class III, or stronger as determined by the horizontal alignment requires greater deflection, design engineer. radius pipe on curved alignment should be used. 5. Corrugated metal and plastic pipe will not be allowed beneath pavement in public easements and right-of- way areas.

40 Section 3 Roadway Drainage Design approved bytheDirector. Laterals shallnotoutfallinto downstreaminletsunless laterals arenomorethan½thediameteroftrunkline. junction structuremustbeprovidedunlesseachofthe same jointlocalizesheadlosses;however, amanholeor Connecting morethanonelateralintoastormdrainatthe being connectedintoaproposeddrainagesystem. proposed lateralsandinlets,forallexisting The hydraulicgradelineshallbecalculatedforall (12 feet orless)crossingutilitylinesshallbeprofiled. including theHGLandutilitycrossings.Shortlaterals profiles shallbedrawnshowingappropriateinformation shall notenterthecornersorbottomsofinlets.Alllateral utilities orstormsewerdepthrequireotherwise.Laterals be fourfeetfromtopofcurbtoflowlineinlet,unless degree (60°)anglefromthestreetside.Lateralsshall shall entertheinletandstormdrainmainata60 Inlet lateralsleadingtostormsewers,wherepossible, requirements inSection3.2.1. storm eventofthecontributingareaandmeetdrylane Laterals aredesignedtoconveythe1%annualchance 3.6.3 LateralDesign 9. 8. 7. 6. list ofapprovedsoftware. of stormdrains.SeetheCityDallaswebsitefora City approvedsoftwarecanbeusedtoaidindesign as directedbytheDirector. additional erosioncontrolmeasuresmayberequired In areaswherehydraulicjumpsareanticipated, for thisdeterminationisnotcoveredinmanual.) determined andnotedontheplans.(Theprocedure location ofanypotentialhydraulicjumpsshallbe partial flow. Ifsupercriticalflowisanticipated, the The flowregimeshallbedeterminedforallpipesin for undergrounddetentionguidelines. by theDirectorpriortoinstallation.SeeSection6.4 detention shallbesubmittedforreviewandapproval Storm drainpipetypeproposedforunderground situations withtheapprovalofDirector. or lessthanrequiredcovermaybeallowedinspecial calculate therequiredcover. Directtrafficboxsections pipe. Itistheresponsibilityofdesignengineerto the expectedloadsandsupportingstrengthof pipe covershouldbebasedonthetypeofused, when nopavementisanticipated.Asageneralrule,the subgrade ofthepavement,orfromgroundsurface proposed pavementandshallnotencroachonthe culverts shallbeatleasttwofeetfromthebottomof The coveroverthecrownofcircularpipeandbox g =accelerationduetogravity(32.2ft/s V changes. Laterals in partial flow must be designed appropriately. the mainchangesduetoconduitsizeordischarge are madetothehydraulicgradelinewhenevervelocityin progress upstreamusingManning'sformula.Adjustments the downstreamstartinghydraulicgradelineelevationand Calculations ofthehydraulicgradelineinmainbeginfrom hydraulic gradientalongthestormdrainsystem. to includethesevaluesinaprogressivecalculationofthe of accuratedeterminationsheadlossesatjunctionsis system fromitsinitialupstreaminlettooutlet.Thepurpose accounted forbythecumulativeheadlossesalong or byinterferencewithflowpatternsatjunctions,mustbe through resistanceofflowinpipes,bychangesmomentum In stormdrainsystemsflowingfull,alllossesofenergy losses canbeexpressedasafunctionofvelocityhead. will causeminorheadlosses.Ingeneral,these inlets, manholes,junction,bends,andenlargementsthat outlet, itwillencounteravarietyofstructuressuchas system attheupstreaminletuntilitdischarges From thetimestormwaterfirstentersdrainage 3.6.4 HeadLosses g =accelerationduetogravity(32.2ft/s V =velocityinlateral(ft/s) H the hydraulicgradeoftrunklineatjunctionplus In determiningthehydraulicgradientforalateral,beginwith V following formulas, and othervelocitychangeswillbecalculatedbythe Hydraulic gradeline"losses"wyes,pipesizechanges, be appliedasshowninFigure 3.17. calculated usingequations3.31, 3.32,and3.33,will Head lossesforlaterals,wyes, andenlargementsshallbe minimum of0.5feetbelow the topofinlet. The hydraulicgradelinewithintheinletshouldbea lateral isinfullflow, thelossesforinletare: calculated usingManning'sEquation.Ataninletwherethe flow, thehydraulicgradeisprojectedalongfrictionslope Where V 2 1 L =downstreamvelocity(ft/s) =upstreamvelocity(ft/s) duetothevelocitychange.Wherelateralisinfull Where V 1 V 1.5V ____ 2 2g

(Equation3.33) V ___ 2g 2 2

. = 0.1

- V ___ 2g 1 2 H =

H Dallas DrainageDesign Manual L Euto 3.32) (Equation L (Equation3.31) 2 2 ) ) 41

5. All precast manhole structures will be built in Tree-box filters should be located upstream of stormwater conformity to the North Central Texas Council of inlets to allow for bypass and underdrains to enter the Governments (NCTCOG) Standard Specification for downstream inlet and should be set back a minimum of Public Works Construction, latest addendum. 3 feet from buildings and property lines.

6. The size difference between a manhole and the largest adjoining pipe should be no less than 2 feet.

7. Maximum manhole size should be determined based upon a cost comparison between a manhole and junction box.

8. A minimum outside clearance of 1 foot should be provided between pipes connecting into a manhole.

9. Manholes on junction boxes, box culverts and horseshoes should be located toward the side of the structure such that the steps descending into the structure are aligned vertically. Steps should be made of either plastic or rubber coated steel.

42 Section 3 Roadway Drainage Design Manhole onMainLine 90˚ Lateral Figure 3.18HeadLossesforJunctionBoxes,Manholes,andBends Manhole onMainLine 90˚ Lateral (see enlargedfigureinAppendixA.7) Head Losses&GainsforLaterals Head Losses&GainsforLaterals (see enlargedfigureinAppendixA.7) Figure 3.17HeadLossesinLaterals,Wyes,andEnlargements 60˚ Lateral 60˚ Lateral 45˚ Lateral Note 45˚ Lateral Note h =V h =V h =V h =V (see enlargedfigureinAppendixG) (see enlargedfigureinAppendixG) 3 3 H H H H H H 2g 2g 2g 2g L L L L L L 2 2 2 2 =LB =1.5V =LB =V =1.5V =V 2 2 2 2 -0.5V -0.5V -0.35V -0.35V 2g 2g 2g 2g 2 2 2 2 2g 2g 2g 2g -V -V * * 1 1 (see enlargedfigureinAppendixG) (see enlargedfigureinAppendixG) 2 2 S S 1 1 2 2 2g 2g 2 2 2 2 Q Q

1 1 f f 2 2 1 1 B B

,V ,V

Q Q

1 1

,V ,V

1 1 H H H H H H 90 90 L L L L L L =LC =LC =V =V =LA =LA 4g 4g Plan Plan 2 2 Section Section 2 2 Q Q -V -V Q Q * * * * 3 3 S S S S 4g 4g 3 3 1 1 f f f f 2 2 C C A A h =V h =V Q Q 2 2

,V ,V

Q Q

2 2

Main HG Line Main HG Line

h h 2g 2g

,V ,V 2 2

2 2 C C

2 2

L L -0.25V -0.25V Main Main 2g 2g QA, VA, SA QA, VA, SA Q Q aries aries

1 1 2 ,V 2 ,V 2 2 LA LA 2 2 Inle HGLinesulealeas Inle HGLinesulealeas Note Note ˚ Bend ˚ Bend erissin erainageengineer en Benseusenlie Hea lssalieaeginning erissin erainageengineer en Benseusenlie Hea lssalieaeginning h =0.50 ˚ Bend h =0.50 ˚ Bend h =0.80 h =0.80 C C

L L Laeral Laeral QB, VB,SB QB, VB,SB Mitered Bends Mitered Bends 05 elinle 05 elinle 2g 2g V V LB LB Dallas DrainageDesign Manual 2g 2g 2 2 V V 2 2

2 2 2 2

3˚ Bend ˚ Bend 3˚ Bend ˚ Bend h =0.45 h =0.45 h =0.60 h =0.60 En En ie ie QC, VC,SC QC, VC,SC LC LC Q Q 2 2 ,V ,V 2 2 3 3 2g 2g V V 2g 2g V V 2 2 2 2 2 2

43 2 2

Culverts shall be designed using the approved list of programs provided on the City of Dallas website or Federal Highway Administration (FHWA) nomographs in Hydraulic Design of Highway Culverts, Third Edition (HDS 5). The remainder of this section provides information necessary for the hydraulic design of culverts.

If designing a culvert using HEC-RAS, please refer to 3.7 Section 4.1 for guidance on modeling structures. CULVERT 3.7.3 Hydraulic Controls 3.7.3.1 Inlet Control HYDRAULIC DESIGN Inlet or entrance control occurs when a culvert is capable of carrying more flow than the inlet will accept and the 3.7.1 General culvert is hydraulically steep (critical depth is greater than normal depth). The function of a culvert is to convey surface water under a roadway, railroad, or other embankment. In addition to When the culvert is under inlet control, the control section the hydraulic function, the culvert must carry construction, is just inside the entrance of the culvert. Hydraulic roadway, railroad, or other traffic and earth loads. characteristics downstream of the inlet control section do not affect the culvert capacity. The inlet geometry, including The material selected for a culvert depends upon barrel shape, cross-sectional area, and the inlet edge various factors, including durability, structural strength, condition represent the major flow controls. If the flow of the roughness, bedding condition, abrasion and corrosion culvert is a free surface flow, then critical depth will occur resistance, and water tightness. The most common at or near the control section. Downstream of the control culvert material used is Class III reinforced concrete. section and a free surface flow, the flow will be supercritical and a hydraulic jump may occur within the culvert. Another factor that significantly affects the performance of a culvert is its inlet configuration. The culvert inlet may The computation of headwater depth, the depth from the consist of a culvert barrel projecting from the roadway fill culvert inlet invert to the energy grade line, is complex or mitered to the embankment slope. Other culvert inlets and dependent upon the type of culvert and the ratio of have headwalls, wingwalls, and apron slabs or standard the headwater depth to the culvert height. The TxDOT end sections of concrete. Hydraulic Design Manual provides a detailed description of inlet control computations for various conditions. A careful approach to culvert design is essential, both in new land development and retrofit situations, because 3.7.3.2 Outlet Control culverts often significantly influence upstream and downstream flood risks, floodplain management, and Outlet or exit control occurs when a culvert is not capable public safety. of carrying as much flow as the inlet will accept.

When the culvert is under outlet control, the hydraulic 3.7.2 Design Frequency grade line inside the culvert at the entrance exceeds critical depth. The headwater of a culvert with outlet The culvert(s) shall be designed for the 1% annual control is determined by the frictional slope, entrance and chance storm event. Channels upstream and downstream exit geometry, and tailwater level. of culverts must contain the design storm and freeboard. Culverts shall not increase the water surface elevation of the 1% annual chance storm event flow.

44 Section 3 Roadway Drainage Design h g =gravitationalacceleration(32.2ft/s v =velocity(ft/s) h The outletdepth,H h S H exit loss. When tailwatercontrols,thefollowingformulaincludes h HW h H L =culvertlength(ft) h the outletdepth. culvert outlet.TheconditionsinTable 3.4willdetermine h TW =tailwaterdepth(ftabovedatum) h at theoutlet(ft) entrance (ft) VO O TW v va O f vi e =frictionalheadlosses(ft) O O =velocityhead(ft) =entranceheadloss(ft) =velocityheadintheentrance(ft) =exitheadloss(ft) =culvertslope(ft/ft) =velocityheadofflowapproachingtheculvert =watersurfaceatoutlet(ftabovedatum) =depthofhydraulicgradelinejustinsidetheculvert =velocityheadinsideculvertatoutlet(ft) =velocityheadintailwater(ft) H OC O

= headwaterdepthduetooutletcontrol(ft) W H = TW + OC h v h = = h e [ + O TW (Equation 3.34) 2g V isthehydraulicgradelineinside _ + h 2

vi ]

h + O (Equation3.35) ∑ h - h f VO

- S (Equation3.36) O L 2 ) + H O h - va Table 3.4OutletDepthConditions soffit oftheculvertoutlet. tailwater higherthancritical depthandlowerthanthe is present,andiftheculvert isonasteepslopewith is insubcriticalflow, backwaterfrom theculvertoutlet The headwatermaybeaffected onlywhentheculvert outlet depth.Normaldepthoccursintheculvert. With thisconditionthebackwaterprofileisbasedon the watersurfacethroughculverttoentrance. standard stepbackwateranalysiscanbeusedtocalculate With afreesurfaceflowoccurringintheculvert Type A–FreeSurfaceFlow pages andinFigures3.19–3.22. These conditionsarefurtherexplainedonthefollowing - - - - within theculvert: There arefour(4)differentflowconditionsthatoccur 3.7.4.1 EnergyLossThroughCulvert 3.7.4 EnergyGradientAnalyses - - - - culvert atoutlet (d exceeds criticaldepth Tailwater depth(TW) outlet critical depth & tailwaterisbelow than topofthebarrel Uniform depthislower than topofthebarrel Uniform depthishigher depth (d is lowerthancritical Tailwater depth(TW) critical depth & tailwaterexceeds than topofthebarrel Uniform depthislower c Type AB–FreeSurfaceFlowatoutletandfullflowinlet. inlet, and Type BA–FullFlowatoutletandfreesurfaceflow Type B–FullFlowinConduit Type A–FreeSurfaceFlow ) intheculvertat c ) inthe If hydraulically mild Slope is hydraulically mild Slope is hydraulically steep Slope is hydraulically steep Slope is hydraulically steep Slope is And Dallas DrainageDesign Manual Equation 3.36 depth basis the tailwateras Equation 3.36,using using Equation3.36. (D) anddepth of thebarreldepth Set H Set H control isnotlikely Ignore, asoutlet Set H Set H o o o o using ascritical using as thehigher Then 45

hvi HW OC h h hvo o tw TW

Figure 3.20 Outlet Control, Fully Submerged Flow

hva Energ Grae Line he Hrauli Grae Line hvi = hvo S f hf

HW OC TW ho

htw

H D O

SO L SO

46 Section 3 Roadway Drainage Design Figure 3.22HeadwaterduetoFullFlowatInletandFreeSurfaceOutlet Figure 3.21PointatWhichFreeSurfaceFlowBegins HW HW S h O h OC va va L OC f h h vi e h h vi e S L Hrauli GraeLine Energ GraeLine Full FlBegins O f Fl Begins Free Surae L L f Free SuraeFl D S Energ GraeLine D f Hrauli GraeLine h vo H h h h vo fp ff O Dallas DrainageDesign Manual ∑h TW f TW H h h h O tw o ff 47

hf = Sf L (Equation 3.37) using the standard step backwater method. head loss due to friction in the culvert barrel (ft) hf = With the water surface (Hi ) or di (shown on Figure 3.22 below) at the culvert inlet, the headwater elevation at the friction slope (ft/ft) Sf = entrance can be calculated. L = length of culvert containing full flow (ft) Type AB – Free Surface at Outlet and Full Flow at Inlet

Hi = HO + hf - SO L (Equation 3.38) If the frictional slope is greater than the culvert slope and the outlet water surface H is less than the culvert soffit at depth of hydraulic grade line at inlet (ft) o Hi = the outlet, calculate the using the following steps. Hi outlet depth (ft) HO = Step 1 – Start with the outlet depth . Ho friction head losses (ft) hf = Step 2 – Use a standard step backwater analysis to determine the point along the conduit where the water S = culvert slope (ft/ft) O surface will intersect the soffit. L = culvert length (ft) Step 3 – At this point along the culvert length, the 2 remaining culvert length L is substituted for L in the ______Qn f Sf = (Equation 3.39) Equation 3.37 to determine h in Figure 3.22. ( 1.486 R2/3 A ) ff Step 4 – With the hydraulic grade line at the culvert inlet, S = friction slope (ft/ft) f the headwater elevation at the entrance can be calculated. Q = flow in pipe (cfs) n = Manning’s ‘n’-value

R = hydraulic Radius (A / wetted perimeter) (ft)

A = area of the pipe (ft2) Type BA – Full Flow at Outlet and Free Surface Flow at Inlet If the frictional slope is less than the culvert slope and the outlet depth is greater than the soffit of the culvert ( HO ) at the outlet then the culvert may flow full for a portion of its length.

48 Section 3 Roadway Drainage Design h culvert atinlet(ft) g =theaccelerationduetogravity(32.2ft/s ( h h The entrancelossshouldbecalculatedusingEquation3.42. HW The culvertinletheadwater( 3.7.4.2 EnergyBalanceatInlet H determine theappropriateheadwater. design engineercancalculatetheapproachvelocityand a conservativeapproachforheadwaterdepth.The the headwaterandenergygradelineareequal.Thisis to theculvertinletcanbeassumedzero(0),thus Generally theapproachvelocityofupstreamchannel entrance (ft) culvert entrance,H using Equation3.41.Withthehydraulicgradelineat V C h h e va e vi i e HW i =entranceloss =entranceheadloss(ft) vi =depthofhydraulicgradelineimmediatelyinsidethe =entrancelosscoefficient(see Table 3.5) =velocityheadintheentrance(ft) =velocityheadofflowapproachingtheculvert = flowvelocityinsideculvertinlet(ft/s) OC ) canbecalculated. OC =headwaterdepthduetooutletcontrol(ft) H = h e i C = + i , thevelocityheadatentrance h e [ vi + V 2g _ i

] h Euto 3.42) (Equation HW e - OC

h va ) canbecalculated (Equation3.41) 2 ) Table 3.5EntranceLossCoefficients Wingwalls parallel(extensionofsides) Wingwalls at10°to25°barrel Wingwalls at30°to75°barrel Headwall paralleltoembankment(nowingwalls) Box, ReinforcedConcrete Side- orslope-taperedinlet Beveled edges,33.7°or45°bevels End-Section conformingtofillslope unpaved slope Mitered toconformfillslope,pavedor Headwall orheadwallandwingwallssquare-edge Projecting fromfill(noheadwall) Pipe orPipe-ArchCorrugatedMetal Side- orslope-taperedinlet Beveled edges,33.7°or45°bevels End-Section conformingtofillslope Mitered toconformfillslope Rounded (radius=D/12) Headwall orheadwallandwingwalls Projecting fromfill,sq.cutend Projecting fromfill,socketend(groove-end) Pipe, Concrete Type ofStructureandDesignEntrance Side- orslope-taperedinlet Square-edged atcrown Square-edged atcrown top edge Crown edgeroundedtoradiusofD/12orbeveled Square-edged atcrown beveled edgeson3sides Rounded on3edgestoradiusofD/12orB/12 Square-edged on3edges Square edge Socket endofpipe(groove-end) Dallas DrainageDesign Manual Coefficient 0.2 0.7 0.5 0.2 0.4 0.2 0.5 0.2 0.2 0.5 0.7 0.5 0.9 0.2 0.2 0.5 0.7 0.2 0.5 0.2 0.5 0.3 C o 49

dO = D

The calculation of the amount of flow that passes through AO the culvert and the remaining portion of flow that overtops the roadway is an iterative process. 3.7.4.4 Depth Estimation Approaches Use Equation 3.44 to determine the average depth between headwater and low roadway elevation for the roadway. For inlet control under steep slope conditions, estimate the (Hh ) depth at the outlet using one of the following approaches: 1.5 Q = kt C L Hh (Equation 3.44) Use a standard step backwater method starting from Q = discharge (cfs) critical depth (dC ) at the inlet and proceed downstream to the outlet. If the tailwater is lower than critical depth at the k = over-embankment flow adjustment factor (see Fig 3.25) outlet, calculate the velocity resulting from the computed t depth at the outlet. If the tailwater is higher than critical C = discharge coefficient (3.0 for roadways) depth, a hydraulic jump within the culvert is possible. Section 3.7.5 discusses a means of estimating whether L = horizontal length of overflow (ft) the hydraulic jump occurs within the culvert. If the (this length should be perpendicular to the overflow direction) hydraulic jump does occur within the culvert, determine average depth between headwater and low roadway the outlet velocity based on the outlet depth, d = H . Hh = O O elevation (ft) Assume uniform depth at the outlet. If the culvert is long enough and tailwater is lower than uniform depth, Ht = average depth between tailwater and low roadway uniform depth will be reached at the outlet of a steep elevation (ft) slope culvert. For a short, steep culvert with tailwater If the tailwater is sufficiently high, the adjustment factork , lower than uniform depth, the actual depth will be higher t determined by Figure 3.25, would reduce the discharge

50 Section 3 Roadway Drainage Design and outletcontrol ofaculvertisshownin Figure 3.28. A sampleplot of theheadwaterversusdischarge forinlet outlet controlthatwillvarywith thedischarge. The performancecurveisa combinationofinletand 3.7.4.7 PerformanceCurves Figure 3.27CrossSectionofFlowOverRoadway Figure 3.26RoadwayOvertoppingwithHighTailwater Figure 3.25Over-Embankment FlowAdjustmentFactor over theroadway. ForvaluesofH adjustment factork the roadway. used todeterminetheflowthroughculvertandover The useofHEC-RASorotherapprovedmodelscanbe into segmentsforthecomputationofweirflow. as showninFigure 3.26,mayneedtobebrokendown HW k t L 10 0 05 1 08 h (see enlargedfigureinAppendixA.7) (see enlargedﬁgureinAppendixG) 1 H L h 2 Culer aer Surae t isone(1).Roadwayembankments, h Rae 2 L H 3 t 09 /H t h

/ H 3 h h below0.8,the Roadway Proﬁle L 4 h 4 H t L 5 TW 10 V h inside oftheculvertoutletisbasedonEquation3.45. V hydraulic gradelineinsidetheculvertatoutlet(ft) Figure 3.28Typical PerformanceCurve through adetentionbasinwithculvertoutlet. useful forariskassessmentorroutinghydrograph from inletcontroltooutletcontrol.Thisinformationis With varyingdischargetheculvertsystemmaychange flow attheoutlet andtheculverthasahydraulically steep If theculverthas afreewatersurfacewith subcritical 3.7.5.1 SubcriticalFlow andSteepSlope 3.7.5 FlowRegime Determination g =accelerationduetogravity(32ft/s K =losscoefficient(1.0forexitlosses) H line elevation(H coefficient variesfrom0.5to1.Thestartinghydraulicgrade between thetailwaterandculvertoutlet.Theexitloss An exitlossshouldbeconsideredatthehydraulicinterface 3.7.4.8 ExitLossConsiderations O TW O O 0 H =exitloss(ft)

=culvertoutletvelocity(ft/s) =outletdepth-fromtheculvertflowlineto =velocityinoutfall(tailwatervelocity)(ft/s) O = h O TW = + o ) attheinterfacebetweenoutsideand K V ___ TW 2g V Oule Cnrl _____ O + 2

2g - V Discharge h

TW O

- (Equation 3.46) 2 V 2g __

O Dallas DrainageDesign Manual 2

(Equation3.45) 2 ) Inle Cnrl 51

2 To minimize the undesirable backwater effects and erosive A = cross-sectional flow area (ft ) conditions produced where the total width of box culverts is less than the bottom width of the channel, a transition d = distance from water surface to centroid of flow area (ft) upstream and downstream of the culverts must be Figure 3.29 Momentum Function and Specific Energy provided. The transition should have a minimum bottom width transition of 2 to 1 and include warping of side slopes M = M ∆E 1 S E E as required. The 2 to 1 transition is 2 along the centerline S 1 of the channel and 1 perpendicular to the centerline. D D Where multiple box configurations of 3 or more boxes are ds utilized, sedimentation often occurs within some of the boxes. This typically occurs because during low discharges, dc d flow spreads out and slows down relative to upstream 1 channel velocities. To prevent this occurrence, the 50% Speciﬁc Energy annual chance storm event velocity through the box culvert 1 = flow depth shall be a minimum of 3 ft/s. Additionally, the 50% annual chance storm event velocity within the culvert shall not be critical depth C = less than 50% of the velocity within the channel upstream of S = sequent depth the culvert prior to the beginning of channel transition to the culvert. Deviations from this criterion that may be dictated

52 Section 3 Roadway Drainage Design Figure 3.30DeterminationofSequentDepth Figure 3.31SolutionforCircularConduits T =Dsin(cos A=

y’1= y1 /D D y’1= y1 /D __ 8 01 02 0 04 05 06 07 08 09 10 Fr

2 01 02 0 04 05 06 07 08 09 10

01 1 [ 01 = 2cos √ = = d' A'=

N u _ gD ______-1 __

N u D __ D (1- 5 A (Equation 3.49) Q d A' 2

-1

T 1 ( 3 __ 2d D /T 02

(Equation 3.50) 2d-D ____ T (Equation 3.53)

) -sin 0

(Equation 3.52) ) 0 ) 04 ß (Equation3.51) ( 2cos 04 06 -1 (1- fr 08 1 06 =1 y __ 2d D

1 y’ D

fr ) 2 08 = y ) 1 2 ] =1 y

2 1 / D y’ D 3 2 2 = y T g =gravitationalconstant(32.2ft/s Q =discharge(cfs) T =widthofwatersurface(ft) Fr =Froudenumber d =depthofflow(ft) D =pipediameter(ft) A A =sectionareaofflow(ft Fr 2 1 1 =widthofwatersurfaceatsupercriticalflowdepth(ft) =areaofflowatsupercriticaldepth(ft 1 =Froudenumberatsupercriticalflowdepth 2 4 / D 3 2 5 4 5 4 6 6 7 5 4 8 8 10 2 5 ) 6 9 6 10 Dallas DrainageDesign Manual 7 2 8 ) 20 8 10 9 2 10 ) 20 53

2. Headwalls with wingwalls and aprons (Type B) shall be 2. Normal water surface elevation used where the approach velocity is from 6 to 12 ft/s 3. Channel lining and downstream channel protection is recommended. 4. Alignment of pipe to channel 3. Special headwall and wingwall configurations will be required where approach velocities exceed 12 ft/s, 5. Erodibility of channel and where the flow must be redirected in order to enter the culvert more efficiently. 6. Downstream channel degradation that may undermine the proposed outfall While the immediate concern in the design of headwalls, wingwalls, and endwalls is hydraulic efficiency, Creative approaches to engineering design of outfalls are consideration should also be given to the safety aspect of encouraged in order to produce the most cost effective culvert end treatments. The use of flared and / or sloped and environmentally acceptable system. As an example, end sections may enhance safety significantly, since the if there is stable rock in a creek bottom, the system could end section conforms to the natural ground surface. For outfall at the rock line. Or, if there is concrete channel any headwall adjacent to pedestrian traffic, either 6-gauge lining, the pipe could be brought to the concrete at a galvanized steel fencing (251D-1) or a guard rail shall be reasonable grade. installed. Fence poles shall be set in concrete at the time of construction. For any headwall adjacent to vehicular The outfall for a storm drain system should discharge traffic, a guard rail must be installed or safety end into a natural low, existing storm drainage system, or treatment designed per TxDOT standards. a channel. The start of the HGL for the storm drain system begins at the outfall. The design engineer should determine the tailwater for the downstream drain to find the impact on the proposed outfall.

A low tailwater elevation is typically the worst-case scenario for providing outfall protection for the prevention of erosion. Therefore, assumption of a 1% annual chance event HGL on the receiving stream may lead to an underestimate of the range of velocities expected at an outfall. For this reason, regardless of whether a coincident peak analysis is used for determining the starting HGL for an enclosed system hydraulic grade line calculation, Table 3.4 should be used for establishing the tailwater HGL for use in outfall design. 54 Section 3 Roadway Drainage Design with highvelocities.Energyis dissipatedthroughthe type energydissipatorthatcan beusedatoutlettransitions to reduceenergy. Abaffledoutletisonetypeofimpact- obstruction (baffle)thatdiverts theflowinmanydirections Impact-type energydissipators directthewaterintoan which designguidelinesarenotgiveninthismanual. accepted referenceforthedesignofenergydissipators for of StillingBasinsandEnergyDissipators(1984)asan of Reclamation’s publicationsontheHydraulicDesign the structure.TheCityofDallasrecognizesBureau water withoutdamagingthestructureorchannelbelow dissipators mustbeabletoslowtheflowoffastmoving specific energyofflowingwater. Effectiveenergy Energy dissipatorsareusedtoeliminatetheexcess 3.8.3 EnergyDissipators for theselectionofcloggingfactors. TxDOT HydraulicDesignManualprovidessomeguidance be used,appropriatecloggingfactorsmustapplied. clear zonerequirements.Ifsafetyendtreatmentsareto the TxDOTRoadwayDesignmanualforadiscussionof Safety endtreatmentsshouldbeconsidered.Referto used ifallothercriteriaaresatisfied. discharging intoawaterway. Precastheadwallsmaybe aligned withthedirectionofreceivingflowwhen as determinedbysiteconditions.Headwallsshouldbe flared orwarped.Theymaynotrequireaprons, reinforced concreteandmaybeeitherstraight-parallel, waterway opening.Allheadwallsshallbeconstructedof and topreventadjacentsoilfromsloughingintothe scour resultingfromexcessivevelocitiesandturbulence to hydraulicandsoilpressures,controlerosion to anchortheculvertinorderpreventmovementdue The normalfunctionsofproperlydesignedheadwallsare 3.8.2 Headwalls/PipeEndTreatment where embankmentslopesexceed3:1. generally necessaryaroundheadwallsandisrequired Provide headwallsforallstormseweroutfalls.Riprapis allowable velocityperTable 5.1. channels wheretheoutfallvelocityexceedsmaximum Outfall protectionisrequiredforalloutfallstoopen of soilsattheoutfalllocationanddesignaccordingly. erosion. Thedesignengineershouldbeawareofthetypes downstream directiontoreducetheturbulenceand should bepositionedinthedownstreamchannel the downstreamchannel.Theoutfallofstormdrain controls shouldbeusedwhenerosionmightoccurin cause erosiontothedownstreamchannel.Velocity The dischargevelocityfromtheoutfallshouldnot sized forwhicheverisgreater. this informationisnotknown, theriprapapronshouldbe not, maximumtailwaterconditions shouldbeused.If elevation islowerthanthecenterline ofthepipe,andif minimum tailwaterconditions ifthetailwaterflow respectively. Theriprapaproncanbedesignedto used forminimumormaximumtailwaterconditions, nomograph (Figure3.32andFigure3.33)shouldbe determined bythefollowingmethods.Theappropriate with anydesignreferencesusedinthedesign. are tobeprovidedtheCityofDallasforreview, along demonstrating theexpectedeffectivenessofmethods is encouraged.Ifothermethodsareutilized,calculations protection. Creativityanduseofothertypesprotection more commontypesofenergydissipation/outfall Design guidanceisprovidedbelowforseveralofthe to appearance. parks orresidentialareasmustgivespecialconsideration maintenance. Thedesignofoutletstructuresinornear All energydissipatorsshouldbedesignedtofacilitate culverts tooverlandsheetfloworchannels. energy dissipationandaretypicallyusedattransitionsfrom energy byhydraulicjump,areaneconomicaloptionfor riprap-lined scour hole. Riprap aprons, which also dissipate are acommonformofenergydissipationthatconsists weir orsillplaceddownstreamoftheoutfall.Riprapbasins where theflowplungesintoapoolofwatercreatedby conjugate depth.Stillingbasinsarestructuresofthistype jump whenitencountersatailwaterconditionequaltothe moving insupercriticalflowisforcedintoahydraulic dissipate excessenergy. Inthistypeofstructure,water Other energydissipatorsusethehydraulicjumpto be smallerandmoreeconomicalstructures. systems, spillways,ordropstructures.Theyalsotendto be mosteffectiveforoutfallsofenclosedstormdrainage Impact-type energydissipatorsaregenerallyconsideredto energy dissipatorsshouldincludealow-flowoutfall. shields, roughnessrings,andoutletweirs.Impact-type type energydissipatorsincludebaffledaprons,splash impact aswelltheresultingturbulence.Otherimpact- The apronsizeandmedianriprapdiameter potential forerosiondownstream. the flowratherthanmoveconcentratedand depth, andriprapsizemustbesufficienttofullydissipate water hitsandmovesacrosstheapron.Thelength,width, roughness ofthematerialandexpansionflowas culverts tonaturalchannels.Energyisdissipatedbythe Flat riprapapronsareusedfortransitionsfrompipesor Riprap Aprons 3.8.3.1 RiprapAprons/Basins Dallas DrainageDesign Manual , d 50 , canbe 55

Figure 3.32 Design of Riprap Apron under Minimum Tailwater Conditions

Oule Pie 3D Diaeer O d=36 d=42 d=48 d=54 d=60 d=66 d=72 d=78 d=84 d=90 d=96 W = DO + 0.4La 120 (DO ) 110 La Tailaer 0.50o 100 90

80 d=30 a

70 d=24 d=27

60 d=21

50 d=18 A L d=15 40 d=12 0

20 2

10 v=30

v=25 1 0 R S 50

v=20 d v=15 v=10 d=12 0 d=15 d=78d=84d=90d=96 d=18 d=21d=24d=27d=30 d=36 d=42 d=48d=54d=60d=66d=72 5 10 20 50 100 200 500 1000 (see enlarged figure in Appendix A.7) D Cures Ma N Be Eralae

56 Section 3 Roadway Drainage Design (see enlarged figureinAppendixA.7) Figure 3.33DesignofRiprapApronunderMaximumTailwater Conditions elevation ofthebasinbelowculvertinlet,h dissipating poolshouldbethelargerof10*h length ofthebasinshouldbelarger15*h used todeterminetheratioofbrinkdepth, greater than0.75.Figure3.34and3.35canbe The ratiooftailwaterdepthtobrinkshouldbe W Design factorsincludemedianriprapsize, and protectionagainstthescourholeenlarging. end ofthebasinservesasadditionalenergydissipation height ordiameteroftheculvert, between theoutletpipeandriprappad,h scoured bythedesigndischarge.Theelevationdifference set totheapproximatedepththatariprappadwouldbe times themedianriprapsize, Oule Pie 0 Diaeer is the diameter of the stormwater outlet. The overall isthediameterofstormwateroutlet.Theoverall 10 20 0 (D

d=12 v=5 d=12 O ) 3D

v=10 d=15 d=15 5 0 O

v=15

d=18 d=18 10 L 40

A L d a Tailaer 50

d=21 d=21 . The length of the energy . Thelengthoftheenergy D .

v=20 d=24 d=24 > 0.50 W =D 50 s 20 , should be 2-4 , shouldbe2-4 d 50 d=27 s

d=27 or3* , and the , andthe s o , which is , whichis s or4* Y O 0 +0.4L , tothe d=30 d=30 W 0 60 , where , where W v=25 0 a . d=36 a

50 d=36 D Using Figure3.36,determineh determined usingManning’s equation. box culvertsandy equation. Iftheoutletisonasteepslope, V The Froudenumbercanbecomputedusingy A =flowareaassociatedwithbrinkdepth,Y Q =designdischarge(cfs) Then, thevelocity, appropriate d=42 0 70

d=42 =velocity(ft/s) 100 d=48 d=48 d

50 V 80 Cures MaNBeEralae

0 d=54 / y d=54 v=30 e = e based on what is available in the area. basedonwhatisavailableinthearea. =(A /2) d=60 V 0 200

d=60 Q / A , canbefoundusingthefollowing d=66

d=66 90 (Equation3.53) 1/2 d=72 d=72 forcircularpipes.Selectan s

v=35 /y

d=78 e . Checkthat2

500 d=84 d=90 v=40 d=90 V

d=96 d=96 0 shouldbe e 0 =y (ft 2 1000 0 ) for for s /d 2 4 50 1 < 4.

57 d50 R S

100 100 8.0 095 6.0 095 Q/D 2.5 = 5.5 7.0 090 090 085 5.0 085 6.0 080 080 3/2 075 4.5 075 Q/BD = 5.0 070 070 4.0 065 4.0 065 3.5 060 3.0 060 3.5 055 055 2.5 3.0 V V 050 O 050 2.0 O 2.5 D 045 D 045 1.5 2.0 040 040 1.5 05 1.0 05 00 00 1.0 025 025 0.5 020 020 0.5 015 015 Q/D 2.5 = 0.0 010 010 Q/BD 3/2 = 0.0 005 005 0 01 02 0 04 05 06 07 08 09 10 0 01 02 0 04 05 06 07 08 09 10 TW/D TW/D D VO TW

Y Brin De Y O O TW D Heig Culer D B i Barrel Brin De YO Q Disarge D Diaeer Culer B TW Tailaer De TW Tailaer De

(see enlarged figure in Appendix A.7) (see enlarged figure in Appendix A.7)

58 Section 3 Roadway Drainage Design Y Determine dimensions of riprap basin based on Figure 3.36. Determine dimensionsofriprapbasinbasedonFigure3.36. Culvert withRelativeSizeofRiprapasaThirdVariable Figure 3.36RelativeDepthofScourHoleVersus FroudeNumberatBrinkof R DS Dnsrea rBasin Rira MaBeReuirenBans&CannelB 05 10 15 20 25 0 0 e d 2 A V FlAreaaBrinCuler Y 50 0 e if ℄ Sein Note: 2≤ 1/2 Rune RrAngularR Te MeianSieReig

Brin DerBCuler Euialen BrinDe FrNnReangularSeins T Y W O (see enlargedfigureinAppendixA.7) >0.75 05 DesignDisargeQ N d h 50 s

≤4 10

0.1 < d Culer Brin

50 / Y

15 e < 0.2

(32.2)(Y Y

0.61 < d

0.21 < d h e s

V 20

0 50 50 / Y / Y

e e < 0.3

) 0.51 < d e < 0.7 0.41 < d 0.31 < d 25 50 / Y 50 / Y 50 / Y e < 0.6 e < 0.5 TW h

0 e < 0.4 s selecting alargersizeofriprap. the basinifneeded.Asmallermaybeachievedby basin exitdepthandvelocity. Extendthelengthof If anallowableexitvelocityisrequired,determinethe D S =riprapspecificgravity V =velocityatexitofdissipator(ft/s) If hightailwaterconditionsareexpected(TW/y basin shouldbeshapedtothenaturalchannelatoutlet. sloping apronshouldbeused.Thewallsandofthe If erosionisexpecteddownstream,ariprapcutoffwallor d have exitvelocitiesexceedingtheallowablechannelvelocity. used forsizingriprapdownstreamofenergydissipatorsthat Section 7.4.4,thefollowingequation(Searcy1967)canbe the typicalstoneriprapdesignmethodologypresentedin more turbulentthaninatypicalchannelreach.Inlieuof Flow downstreamofanenergydissipatorisgenerally between 1.8D Figure 3.37 foradditionaldesigndetails. should bewrappedaroundthetoeofrevetment.See for stretchingasriprapisplacedontop.Thematerial Fabric layersshouldoverlapandplacementallow between largerriprapandthefilterfabrictopreventtears. cohesive soils.Agravelbeddinglayershouldbeplaced Filter fabricisrequiredwhenriprapplacedonnon- of soil,distributeweightmoreevenly, andlimiterosion. underlying soil.Thislayerwouldpreventthemovement Filter fabriccanbeplacedinbetweenthestructureand longer ifthestormwateroutletisdischargingintohightailwater. against highvelocities.Thescourholemaybeshallowerand additional riprapshouldbeuseddownstreamtoprotect 50 30 =medianrocksize(ft) istypically15percentsmallerthanD d 50 = 15 and4.6D 0.692 ____ S -1

( 15 2g V __ . 2

) (Equation3.54) Dallas DrainageDesign Manual 50 . D 0 ≥0.75), 85 shalllie 59

Dissiar Pl 10h r 3W in Arn 5h r W in Cannel 1 Freear s o s o in T Ber Ne A T Rira Ne B

y e1V:2H TW Hrinal 1V:2H hs

2d50 or 3d50 or 2dmax 2d50 or 2d50 or 1.5dmax 1.5ft min Tiene r Sling Te Oinal 1.5dmax 1.5dmax Cnsru I Dnsrea Cannel Degraain Is Aniiae B A C D Ne B

1V:2H 1V:2H Ne Ar Ege 1V:2H W Diaeer r Pie Culer aer Arn a Rira n W Barrel i r B Culer 1 b Sn W San PieAr Culer 1V:2H S c W o Culer 1V:2H Hrinal Au 2

2d50 or 1.5dmax Hal Plan Ne B Ber hs

Naural Cannel S A S Eaae Tis Line W o Baill i Rira 1 2 2d50 or 1.5dmax 2

Ber Reuire Ber Is Reuire Sur Rira 2d or 1.5d Sur Eaae Tis Line 50 max Rira S Baill i Rira S D

N A I Ei eli Basin Is Seiie Een Basin as Reuire Oain Suiien CrssSeinal Area a Sein a Su Ta Qs Crss Sein Area a Sein A Seiie Ei eli

60 Section 3 Roadway Drainage Design Y to one-halftheculvertheight. situations inwhichthedepthofflowatoutletisequal Figure 3.39fordetails.Thisbasinisbestsuitedto conjunction withContraCostaCounty, California.See developed attheUniversityofCalifornia,Berkeley, in outlet withsometailwater. TheContraCostaBasinwas The ContraCostaBasincanbeusedforaculvert Contra CostaBasin For thedesignofstillingbasins,refertoFHWA HEC-14. Figure 3.38SAFStillingBasin Falls (SAF)stillingbasinisshowninFigure3.38. within Froudenumbersfrom1.7to17.TheSaintAnthony tailwater condition.Thesestillingbasinsnormallyoperate a hydraulicjumpwithinthebasin.Thebasinrequires The stillingbasinisusedasanenergydissipatortotrigger Stilling Basin 3.8.3.2 ConcreteAprons/Basins 1 3/8Y Cue Bl Flr rBaleBls W 1 B Y 1 SA SIINGASIN Z Sie all L B 1 /3 L 3/8Y B 0.07 Y En Sill 1 W B2 2 3/8Y W Basin HalPlan 45 Preerre 090 Flare Basin Reangular B3 1 all CuO aries z 1 Y Y 2 3 For thedesignofstillingbasins,refertoFHWA HEC-14. Figure 3.39ContraCostaBasin design methods. Figure 3.40 fordetails.See FHWA HEC-14fordetailed Riprap shouldbeplaceddownstreamofthebasin.See maximum tailwaterisnogreaterthanhalfofthebaffle. in alltailwaterconditionsbutwillperformbestwhen out anybuiltupsediment.Baffledoutletswillwork in thebaffleservetocreateconcentratedflowwash over thetopofbaffleaswellbelowit.Thenotches creating eddies.Athigherdischarges,waterwilloverflow of culvertsorinopenchannels.Runoffhitsthebaffle, USBR Type VIimpactbasin.Itcanbeusedatoutlet and slowvelocities.Abaffledoutletisalsoknownasa vertical hangingbaffleandendsilltoincreaseturbulence A baffledoutletisabox-likestructurethatutilizes 3.8.3.4 BaffledOutlets 1 foot orcriticaldepth(d height. Theheightofblocksshouldbeaminimum the firstrowofblocksshouldbeaminimumculvert of blockshouldbeused.Thedistancefromtheculvertto velocity to6feetpersecondorless.Aminimumof2rows Baffle blocksshouldbeusedtoreducethesubcritical 3.8.3.3 BaffleBlocks outlet structure. should extendacrossthetotalbottomwidthofculvert up withthespacingoffirstrowblocks.Theblocks second rowofblocksshouldbeoffsetsotheblocklines spacing ofblocksshouldmatchtheheightblock.The D y 0 V 0 L ONRA OSA ASIN h 2 1 /2 L D≤W≤3D 2 c ). Thewidthoftheblockand h 1 L B Dallas DrainageDesign Manual y 2 L y 3 3 h 3 V 2 61

1.5:1

1:1

A L = 4/3 (W) W D f = 1/6 (W) e = 1/12 (W)

1:1 e

e L f 2 f 4 f

a S A

f W 5’ min

Fille H Q,V b H = 3/4 (W) c a = 1/2 (W) b = 3/8 (W) f f c = 1/2 (W)

Prein as S R Diaeer r Prein 1/20 (W) Reuire

62 Section 3 Roadway Drainage Design Table 3.6RiprapApronLengthDownstreamofDropStructures downstream ofadropstructure. used fordeterminingtheminimumlengthofriprapapron and scourfromincreasedturbulence.Table 3.6shouldbe reinforced concreteorripraptoprotectagainsttheerosion of thedropstructure,channelshouldbearmoredwith structure topreventscourandundermining.Downstream must beprotectedupstreamanddownstreamofthedrop hydraulic gradient.Inaddition,thetoewallsofchannel should beprotectedagainsterosionduetothesteep drop. Thechannelsidesadjacenttothedropstructure limit velocityandturbulenceasthewaterapproaches riprap apronshouldbeplacedupstreamofthedropto drop structure,asdrawdownwilloccur. A10footlong at thesite.Thereispotentialforerosionupstreamof analysis shouldbedonetoconfirmthestructuralstability designing dropstructures.Ageotechnicalandstructural Several factorsshouldbetakenintoconsiderationwhen See FHWA HEC-14fordetaileddesignmethods. basin toprovideadditionalenergydissipationifdesired. of 4feet.Bafflesandsillscanbeplacedwithinthestilling erosion. Adropstructureshouldhaveamaximum stilling basinbelowthedropshouldbearmoredtoprevent vertical dropsthatdissipateandslowvelocities.The the effectsofsteepslopesbycreatinggentleand Drop structuresaretypicallyusedinchannelstomitigate 3.8.3.5 DropStructures Maximum UnitDischarge,q (cfs/ft) <15 30 25 20 15 Length ofDownstreamApron, L B 25 20 20 15 10 (ft) drainage area. to holdatleast1inchofrunofffromthecontributing side slopesnosteeperthan2:1.Basinsshouldbesized They shouldhaveaminimumdepthoftwofeetwith methods (e.g.bafflewalls)tohavealongflowpathlength. four timesgreaterthanthewidth,oremployother Sedimentation basinsshouldbesizedtohavealength have ahighpercentageofclayorsilt. Sedimentation basinsmaynotbeeffectivewithsoilsthat 20 acresforatemporarybasinduringconstruction. up to100acresforapermanentengineeredbasinand quality measure.Theycanbeusedfordrainageareas measure onaconstructionsiteoraspermanentwater Sedimentation basinscanbeusedasatemporary solids sothattheydonotenternaturalbodiesofwater. retain runoffandallowforthesettlingofsuspended A sedimentationbasinisdesignedtocollectand 3.8.4 SedimentationBasin that theselecteddesignreducesvelocitiestobelow6ft/s. Other energydissipationmethodsmaybeusedprovided 3.8.3.6 OtherEnergyDissipators contributing area. the 1%annualchancestormeventforupstream temporary sedimentationbasinsarerequiredtoaddress storm, unlesstheyareonlinetoastream.Online Temporary detentionbasinsaredesignedfor2-year regulations, asapplicable. annual chancestormevent.AlldamsaresubjecttoTCEQ Emergency spillwaysshouldbedesignedtopassthe1% should beused. for maintenance.Measurestopreventvectorattraction wetlands. Thesedimentationbasinshouldbeaccessible Sedimentation basinsshouldnotbelocatedinstreamsor be aminimumof6hoursandmaximum24hours. Unless designedwithapermanentpool,drawdownshould Dallas DrainageDesign Manual 63

SECTION 4 Bridge Hydraulic Design

Dallas Drainage Design Manual 65 4.1 4.2 GENERAL DESIGN FREQUENCY

The function of a bridge is to convey surface water under AND FREEBOARD a roadway, railroad, or other embankment. Impact from floating debris must be considered for the structural design of the bridge components. Where proposed streets 4.2.1 Design Frequency cross existing or proposed watercourses, all-weather crossings are required. The design frequency for bridges is the 1% annual chance storm event. The design engineer will analyze both existing and proposed bridge conditions. The U.S. Army Corps of Figure 4.1 Model Cross-Section Locations Engineers’ HEC-RAS modeling software is recommended to analyze a bridge. Other software may be used with Section 4 the approval of the Director. A bridge may increase the depth of flow upstream. Modifications of the channel ZONE 3 downstream and upstream of the proposed bridge may be Section 3 needed to mitigate the upstream impact. (L1+L2)/2 ZONE 2 Figure 4.1 displays the four typical model cross-section L1 L1 Section 2 locations necessary to assess the hydraulic performance of a bridge. Section 1 should be located downstream of the bridge at a point where the expansion of flow from the bridge is expected to be complete. Section 2 should be located a ZONE 1 short distance downstream of the bridge. Section 3 should

be located a short distance upstream of the bridge. Section 2(L1+L2) 4 should be located upstream of the bridge at a point where the start of contraction is expected to occur. Section 1 Typical contraction and expansion values at bridge sections are 0.3 and 0.5 respectively. Abrupt transitions will have higher values. The contraction and expansion values * Adapted from HEC-RAS User's Manual should typically be applied to Sections 2, 3, and 4. Refer to the HEC-RAS Hydraulic Reference Manual for additional guidance related to hydraulic modeling of bridges.

66 Section 4 Bridge Hydraulic Design 1 INTRODUCTION 4.2.2 Freeboard / Minimum

Clearance 2 Freeboard at a bridge is the vertical distance between the HYDROLOGY design water surface elevation and the low-chord of the bridge. The bridge low-chord is the lowest portion of the bridge deck superstructure. The purpose of freeboard is to provide room for the passage of floating debris, extra 3 4.3 ROADWAY

area for conveyance in the event that debris build-up on DRAINAGE DESIGN the piers reduces hydraulic capacity of the bridge, and a factor of safety against the occurrence of waves or floods larger than the design flood. FLOW REGIMES 4

Bridges should be designed with a minimum of 2 feet of BRIDGE freeboard from the low chord to the 1% annual chance 4.3.1 Low Flow Considerations HYDRAULIC DESIGN flood elevation unless a low water crossing is approved by the Director. For the purpose of flow regimes, low flow exists when the water surface is below the low chord of the bridge

For bridges over aesthetic waterways that do not serve a opening. There are three classes of flow for low flow 5 drainage conveyance function (for example, a pond that DESIGN

conditions. See Figure 4.2. OPEN CHANNEL is located off-stream and serves no detention function), there is no freeboard requirement, but overtopping should Class A low flow exists when the water surface is not occur in the 1% annual chance storm event. subcritical from sections 1 to 4.

There are four methods available for assessing hydraulic 6

The design engineer should consider the minimum clear DRAINAGE height from the channel bottom to the low chord to be 6 performance between Sections 2 and 3 as follows: STORAGE DESIGN feet. Additional height should be considered for passage of maintenance vehicles under the bridge to minimize the -- energy equation number of channel access ramps. Low water crossings -- momentum balance must be approved by the Director. 7 -- Yarnell equation, and CONTROL MEASURES -- FHWA WSPRO method. EROSION & SEDIMENT

Class B low flow exists when the water surface passes through critical depth within the bridge constriction between Sections 2 and 3. The flow upstream and downstream of the bridge can be either subcritical or supercritical. 8 FLOODPLAIN & SUMP

Class C low flow exists when the water surface is DESIGN REQUIREMENTS supercritical from Sections 1 to 4. 9 REQUIREMENTS OTHER REGULATORY OTHER REGULATORY 10 SUBMITTAL SUBMITTAL REQUIREMENTS 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 67 APPENDICES Figure 4.2 Bridge Profile with Cross Section Location 4 3 B u Bd 2 1

Q 4.4 CHANNEL CONSTRICTION

Where sloping abutments are utilized, slopes shall be 4.3.2 High Flow Considerations designed per requirements in Section 7.2 for natural High flow exists when the water surface comes into contact channel setback. The Director may approve a steeper with the maximum low chord of the bridge opening. The slope if a slope stability analysis is provided by a Licensed computation would be by the Energy equation or by Geotechnical Engineer that demonstrates stability at the hydraulic equations for pressure and/or weir flow. steeper slope and the abutment slope is lined with hard armoring such as concrete, concrete block mats, stone riprap, or gabions. 4.3.3 Supercritical Flow The width of the main channel between the toe of slope For supercritical flow conditions in a stream or channel, from each abutment shall not be less than the typical the design engineer should confirm that the bridge channel width upstream and downstream of the bridge. opening is clear of bridge piers or other projections and does not impact the flow. If bridge piers or other projections are within the bridge opening, then hydraulic jumps within the bridge structure should be considered and the impacts should be addressed in the bridge design. 4.3.4 Erosive Velocities Velocities within bridge sections are often higher than velocities within the channel upstream of the bridge. Erosion protection as discussed in Section 7 is often required for bridges, as restrictions to open channel velocities also apply to channels under bridges.

68 Section 4 Bridge Hydraulic Design 1 INTRODUCTION 2 HYDROLOGY 3

4.5 4.6 ROADWAY DRAINAGE DESIGN SCOUR BRIDGE DECK 4 Consideration of the scour of soil around a bridge is DRAINAGE BRIDGE critical to the longevity of the structure. The total scour HYDRAULIC DESIGN at a bridge crossing is comprised of three components: Bridge deck drains should: long term aggradation and degradation, contraction scour,

and local scour at piers and abutments. The long term -- Minimize the spread of water into the traffic lanes 5 aggradation and degradation should be assessed and and, at a minimum, meet the street capacity DESIGN accounted for in the bridge scour analysis. requirements described in Section 3.2.1 OPEN CHANNEL

Bridge scour analysis for contraction scour and local -- Prevent the accumulation of significant depth of water scour at piers must be performed. Contraction and pier to reduce hydroplaning scour shall be evaluated and results incorporated into 6 -- Be integrated into the structural deck DRAINAGE structural design. Guidance on contraction and pier scour STORAGE DESIGN can be found in FHWA’s HEC-18. A reduction factor of 0.5 for soils with 11% or more clay can be applied to the -- Reduce drain hazards to bicyclists computed pier scour. Abutment riprap shall be designed -- Be easy to maintain in accordance with the design guidelines in Section 7.4.4 7 in lieu of performing abutment scour analysis. The riprap -- Provide sufficient longitudinal grade abutment toe must be designed to account for any CONTROL MEASURES anticipated contraction scour. Scour analysis will not be -- Avoid zero longitudinal grade and sag vertical curves EROSION & SEDIMENT needed if the channel is concrete lined. on the bridge -- Intercept all flow from curbed street before it reaches bridge 8 -- Not cause erosion within the channel below the bridge FLOODPLAIN & SUMP DESIGN REQUIREMENTS 9 REQUIREMENTS OTHER REGULATORY OTHER REGULATORY 10 SUBMITTAL SUBMITTAL REQUIREMENTS 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 69 APPENDICES 4.7 4.8 ROADWAY OTHER DESIGN OVERTOPPING CONSIDERATIONS

Ideally, the public vehicular roadway adjacent to the Maintenance agreements are required for private bridge should not overtop during the 1% annual chance vehicular / pedestrian bridges over creeks and channels. storm event. In order to prevent roadway overtopping, the profile grade of the roadway, at all points within the The following guidelines pertain to the hydraulic floodplain, shall be a minimum of 1 foot above the energy design of bridges: grade elevation or hydraulic grade line for the 1% annual 1. Side swales in a main bridge opening or relief chance storm event, whichever is greater. All exceptions channels with overflow structures may be used to must be approved by the Director. provide additional conveyance downstream of and through bridges. (Swales are subject to the criteria contained in the Floodplain Ordinance Article V Section 51A-5.100-5.105.)

2. Bents should not be located in the main channel when possible. Bents should be aligned approximately parallel to flow.

70 Section 4 Bridge Hydraulic Design 1 INTRODUCTION 2 HYDROLOGY 3 ROADWAY ROADWAY DRAINAGE DESIGN 4 BRIDGE HYDRAULIC DESIGN 5 DESIGN OPEN CHANNEL 6 DRAINAGE STORAGE DESIGN 7 CONTROL MEASURES EROSION & SEDIMENT 8 FLOODPLAIN & SUMP DESIGN REQUIREMENTS 9 REQUIREMENTS OTHER REGULATORY OTHER REGULATORY 10 SUBMITTAL SUBMITTAL REQUIREMENTS 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 71 APPENDICES

SECTION 5 Open Channel Design

Dallas Drainage Design Manual 73 5.1 5.2 GENERAL OPEN CHANNEL

This section addresses proposed improvements or HYDRAULICS modifications to drainage channels and watercourses that convey storm water runoff. Hydraulic calculations can be performed using software Preservation of creeks in their natural condition is from the City’s approved list (a list of approved software preferred. In the event that it is necessary to utilize can be found on the City’s website). a constructed open channel, it shall be designed to Certain watersheds have hydrologic and hydraulic models convey the full design discharge, the 1% annual chance that are available through the City. Projects proposed storm event. Hydraulic characteristics of open channels within the limits of these watersheds must have the can vary greatly and have a significant impact on the models updated by the design engineer to reflect changes performance of open channels. Section 5.2 provides in flow, channel configuration (including alterations to discussion of open channel hydraulics relative to channel vegetation) and channel structures. design. Open channel design guidelines are provided in Section 5.3. Refer to Section 3.4 for bar ditch and bioswale design. 5.2.1 Flow Classification See Appendix A.3 for further guidance on energy conservation equations and Froude numbers. 5.2.1.1 Types of Flow in Open Channels Open channel flow can be characterized in many ways. Types of flow are commonly characterized by variability with respect to time and space. The following terms are used to identify types of open channel flow:

Steady flow—flow conditions at any point in a stream remain constant with respect to time (Daugherty and Franzini 1977).

Unsteady flow—flow conditions (e.g., depth, velocity) vary with time.

Uniform flow—the magnitude and direction of velocity in a stream are the same at all points in the stream at a given time (Daugherty and Franzini 1977). If a channel is uniform and resistance and gravity forces are in exact balance, the water surface will be parallel to the bottom of the channel for uniform flow.

Varied flow—discharge, depth, or other characteristics of the flow change along the course of the stream. For a steady flow condition, flow is termed rapidly varied if these characteristics change over a short distance. If characteristics change over a longer stretch of the channel for steady flow conditions, flow is termed gradually varied.

74 Section 5 Open Channel Design whichever isgreater. Supercritical flowconditionsshall depth plusfreeboard,orsequent depthwithoutfreeboard, minimum designdepthofa channelshallbethefrictional supercritical flowsareprovidedinSection5.3.The Special considerationsforthedesignofchannelswith. area createshazardsthatthedesignermustconsider. Supercritical flowinanopenchannelurban occur fromtheupstreamtodownstreamdirection. For supercriticalflow, watersurfacecomputations greater erosivepowerthansubcriticalflows. velocities, shallowerdepth,higherhydrauliclosses,and supercritical flows.Supercriticalflowshavehigher Flows withaFroudenumbergreaterthan1.0are divided bythefreewatersurfacetopwidth. area ofthechannelperpendiculartodirectionflow The hydraulicdepthisdefinedasthecrosssectional d =Hydraulicdepth(ft) g =Accelerationduetogravity32.2ft/s V =Meanvelocity(ft/s) in thefollowingequation. a FroudeNumber(Fr).Theisexpressed flow canbeexpressedinadimensionlessquantitycalled The influenceofgravityonfluidmotioninopenchannel hydraulic jumps. following designguidanceforsupercriticalflowand supercritical tosubcriticalflowcannotbeavoided,see are tobeavoidedwherepossible.Iftransitioningfrom Design solutionsthatincorporatesupercriticalflow 5.2.1.3 SupercriticalFlow seek tocreatechannelswithsubcriticalflowregimes. stable naturalchannels,majordrainagedesignshould successful artificialchannelsutilizecharacteristicsof regimes. Consistentwiththephilosophythatmost Most stablenaturalchannelshavesubcriticalflow downstream direction. to theupstreamdirectionasflowcontrolisfrom for subcriticalflowarecomputedfromthedownstream though theycanstillbeerosive.Water surfaceelevations tranquil, lowvelocityflowscomparedtosupercriticalflow, flows. Subcriticalflowsarecharacterizedbyrelatively Flows withaFroudenumberlessthan1.0aresubcritical 5.2.1.2 SubcriticalFlow Fr = √ __

__ V gd

(Equation5.1) 2 1. conditions: a freewatersurfaceischaracterizedbythefollowing Critical flowinanopenchannelorcoveredconduitwith 5.2.1.4 CriticalFlow effects willoccurasaresult. than 1.1unlessanalysesdemonstratethatnoadverse channel Froudenumbersmustbebelow0.9orgreater the Froudenumberisbetween0.9and1.1Therefore, unstable transitionalflowconditionsthatoccurwhen channel improvementsshallbedesignedtoavoidthe flow conditionstooccurnaturally. Inallcases,the where theexistingtopographywillnotallowsubcritical by usingenergydissipatorsinunlinedchannelsareas be provided.Subcriticalflowconditionsmayachieved withstand theturbulencefromdrop,orliningshall structure anddownstreamchannelisdesignedto The designengineermustdemonstratethatthedrop only beallowedinlinedchannelsoratdropstructures. circular channelslocatedinAppendixA.7. curves havebeengivenforrectangular, trapezoidal,and To simplify thecomputationofcriticalflow, dimensionless stability. or slopeshouldbechangedtoachievegreaterhydraulic near critical,withaFroudenumber1.0,theshape not bestable.Indesign,ifthedepthisfoundtoator supercritical flow. Aflowatornearthecriticalstatemay flow, andaslopegreaterthancriticalwillcause A slopelessthancriticalwillcausesubcritical a supercriticalchannel. channel, andwheresignificantobstructionsoccurwithin such asfromanaturalchanneltoconcretelined shape, significantchangesinliningresistanceandslope transitions oftenoccuratrapidchangesincross-section subcritical tosupercriticalflow, orviceversa.These Flow passesthroughcriticaldepthasittransitionsfrom Channels rarelyflowatcriticaldepthforlongreaches. 3. 2. The specificenergyisaminimumforgivendischarge. The Froudenumberisequalto1.0. in achannelofsmallslope. The velocityheadisequaltohalfthehydraulicdepth Dallas DrainageDesign Manual 75

The length and the conjugate depth of a hydraulic n = Roughness coefficient jump are generally of interest to channel designers. If a 2 A = Area of channel cross section (ft ) hydraulic jump is being modeled with hydraulic software, cross-sections should be spaced closer together than P = Wetted perimeter (ft) usual so that the model can accurately identify the expected location of the jump. To compute hydraulic jump R = Hydraulic radius = A/P (ft) parameters for rectangular channels by spreadsheet, the following equations and charts may be used. S = Channel bottom slope (ft/ft) _ Manning’s ‘n’ values are provided in Appendix A.3. Manning's y_2 2 = 1 / 2 (√ 1 + 8 Fr - 1 ) (Equation 5.2) y 1 Equation can also be expressed in terms of velocity by 1 employing the continuity equation, Q = VA, as a substitution Conjugate depth (ft) y2 = in the above equation, where V is velocity (ft/s). Depth approaching the jump (ft) y1 = Approach Froude number Fr1 =

Figure 5.1 Hydraulic Jump Energ Enering u Energ Lss in u E1 Energ Enering u E2 E1 - E2 Fr Frue Nuer V gy D 2 1 1 V y D - D (Height of Jump) E = y + 2 j 2 1 40 2 2 2g y Criial De C y c V 2 3 Seuen Des 2 1 y1,y2 E = y + 1 1 2g y ,y Alernae Des 30 1 3 B y2 20 1 v2 y y I yj 2 10 v1 O yC A y y 1 1 0 10 20 30 40 LJ E H H S E (see enlarged figure(See in Appendixenlarged figureA.7) in Appendix A.7) D

76 Section 5 Open Channel Design (See enlarged figure inAppendixA.7) Figure 5.3LengthofJumpforaRectangularChannel Figure 5.2HydraulicJumpConjugateDepth–Horizontal,RectangularChannel J = y L y 1 100 110 120 130 2 10 20 30 40 0 60 70 80 90 2 10 1 20 0 0 2 2 4 4 6 6 Fr Fr 8 1 - 1 = 8 gy gy V V 1 1 1 1 10 10 Fr 12 1 =0.5J 12 J-1 Dallas DrainageDesign Manual 3 14 -0.5J 14 16 16 77

Channel Type Maximum Side Slopes Maximum Velocities -- Sedimentation basins Earth vegetated 3:1 6 fps -- Between grade stabilizers soils -- Between drop structures Partially lined 3:1 above lining 12 fps Fully lined 2:1 15 fps -- Where access under bridges, culverts, etc. is restricted (NA at drop structures) -- All channels with a bottom width greater than 12 feet

78 Section 5 Open Channel Design Figure 5.4DropSpacingCriteria Figure 5.4 andthefollowingequationsforspacingcriteria. Drop spacingshallbecomputedasfollows.See 5.3.7.1 ChannelDrops lining providedinaccordancewithSection7.4. with thedropshallbecomputedandadequatechannel If dropstructuresareutilized,shearstressesassociated assessed andchannelprotectionprovidedwhereneeded. The potentialverticaldegradationofastreamshallbe 5.3.7 BedControls no adverseeffectswilloccurasaresult. between 0.9and1.1unlessanalysisdemonstratesthat conditions thatcanoccurwhentheFroudenumberis slopes necessarytoavoidtheunstabletransitionalflow In allcases,channelimprovementswillbedesignedwith occur naturally. topography willnotallowsubcriticalflowconditionsto energy dissipatorsinunlinedchannelswheretheexisting Subcritical flowconditionsmaybeachievedbyusing turbulence fromthedroporliningshallbeprovided. that thedropstructureisdesignedtowithstand drop structures.Thedesignengineermustdemonstrate conditions shallonlybeallowedinlinedchannelsorat recommended forallchanneldesigns.Supercriticalflow Slope thatachievessubcriticalflowconditionsare be neededtoprotectthebottomandsideslopes. the designslopetodetermineifadditionalprotectionwill design engineershouldconsiderthechannelstabilityof the requirementsof5.3.3.Forearthenchannels, The channelslopeforconstructedchannelsshallmeet 5.3.6 ChannelSlope truck accessmaysuffice. trucks andloaders.Forsmallditches,footorpick-up the channel.Largechannelsmayneedaccessfordump The typeofequipmentneedingaccessisdependenton H =10’Ma S 1 L D SC S

2 Q Fr Cannel Design Design Cannel Fr L Ma Perissileeli Grae ReuirerV Eising NauralGrae S 2 velocity establishedfromTable 5.1(ft/ft) S (see Figure5.1). depth ofthechannelshouldcontainsequent the channel.Ifchannelbecomessupercritical, determine iftheflowisorwillbecomesupercriticalalong The designengineershouldanalyzechanneldropsto R =Area/wettedperimeter(ft) N =Manning’s ‘n’value Table 5.1 (ft/s) V =Maximumpermissiblevelocityestablishedfrom S by Director) H =Heightofdrop(ft)(Maximum3ftunlessapproved L =Distancerequiredbetweendrops(ft) The spacingoftherowblocksshallbe2H. blocks lineupwiththespacingofupstreamblock. The subsequentrowsofblocksshallbeoffsetsothe blocks aretoextendacrossthetotalwidthofchute. and spacingofthebaffleblockshallbe1.5H.Thechute the criticaldepthto0.9timesdepth.Thewidth The heightoftheblocks,H,shallrangefrom0.8times foot ofchutewidth. 2H:1V to4H:1V.Themaximumflowshallbe60cfsper than criticalvelocity. Thechuteslopeshallfallbetween drop. Theapproachvelocitytothechuteshallbeless shall beusedforthedesignofbaffleblocksonchute For concretechutesonearthensideslopes,thefollowing 5.3.7.2 BaffleChutes 2 1 =Slopeofproposedchannelformaximumpermissible =Actualslopeofchannel(ft/ft) S 2 = L R (1.486 = = ______S

NV H S -

2 2 Euto 5.5) (Equation ⅔ )

2 5.6) (Equation Dallas DrainageDesign Manual 79

3 V1 + 9q-5 0.2H 9 in 1/3H - 2/3H q = Q/W H W 12 a aries

H/2 + 0.2H

3H R = 12” Lain Oinal 4 Rs in 2H W Wi Cue H Heig e ls

Rira

5.3.7.3 Checkdams 5.3.8 Channel Bends Checkdams may be used similarly to drop structures, but Head loss resulting from channel bends shall be they maintain a normal water surface elevations between incorporated into channel hydraulic modeling. Shear drops. Erosion protection shall be provided downstream of stress shall be evaluated. See Section 7.4 for guidance on each drop structure. erosion protection. The following equation can be used to predict maximum scour depth at bends. Figure 5.6 Checkdams d R -1 ___max = 1.5 + 4.5 __ c (Equation 5.7) ( ) H dm Wi Maximum scour depth in bendway pool (ft) dmax =

dm = Mean depth (cross-sectional area / W) (W = reach L average bankfull width) (for the 1% annual chance storm event, or smaller event if it would result in a Refer to Equation 5.5 for spacing of checkdams. higher scour depth estimate)

Radius of curvature (degrees) Rc = Width at meander inflection point (ft) Wi = Allowance for extra freeboard shall be made when the centerline radius of the channel is less than three times the bottom width or for supercritical flow regime. See Section 5.3.11 for guidance on superelevation.

80 Section 5 Open Channel Design B Wi B Wi Figure 5.8ChannelBottomWidthTransitions shall beassessediftheymeettheaboverequirements. occur. Bottomwidthtransitionsduetoculvertsandbridges and assessedtodeterminewhetherahydraulicjumpmay transition mustbemodeledusingCity-approvedsoftware also beaccountedfor. Forsupercriticalchannels,the Potential headlossduetobottomwidthtransitionsshall provided perSection7.4.SeeFigure5.8forguidance. stress anddemonstratethatadequatelininghasbeen an assessmentoftheimpacttransitiononshear W:H ratio,persideofchannel,thedesignershallprovide For alldesignedbottomwidthtransitionsgreaterthana1:3 5.3.10 BottomWidthTransition guidance onmodelingjunctionheadloss. Refer totheHEC-RAStechnicalmanualforfurther be consideredinopenchannelhydraulicmodeling. for guidanceonerosionprotection.Junctionheadlossshall may preventerosionoftheoppositebank.SeeSection7.4 without thepresenceofsignificantmainchannelflowthat adjoining streampeakdischargetoenterthemainchannel and timingofthepeakflowspotentialfor needed. Thisassessmentshallconsidertherelativesize of thejunctionandassesswhethererosionprotectionis Designer shallassesspotentialforerosiononbothbanks Figure 5.7ExampleGeometryforChannelJunction degrees. RefertoFigure5.7forexamplegeometry. Channel junctionsshallhaveamaximumangleof60 5.3.9 ChannelJunctions Expansion Contraction Dnsrea Dnsrea Q

in,1

60 Q In,2 1 Fl Fl 2 2 1 B Wi Usrea B Wi Usrea Q out g =Accelerationduetogravity(32.2ft/s T =Widthofflowatthewatersurface(ft) V =Average approachvelocity inchannel(ft/s) B =Bottomwidthofchannel(ft) d for computingtheextrafreeboard(refertoFigure5.9): subcritical, theapplicantshallusefollowingformula or highvelocitiesareinvolvedandtheflowregimeis Section 7forerosionprotectionmeasures.Wherebends supercritical flow, seeSection5.2.1.3andreferto the bottomwidthorforsupercriticalflowregime.For centerline radiusofthechannelislessthan3times Allowance forextrafreeboardshallbemadewhenthe Figure 5.9Superelevation 5.3.11 Superelevation c. b. a. d R =Centerlineradiusofthebend(ft) 1 2 =Depthofflowattheinsidebend(ft) =Depthofflowattheoutsidebend(ft)

The quantityd calculated withtheaboveformulashallbedoubled. For supercriticalflowregimes,theextrafreeboard backwater thatmayresult. for allheadlosses.Allowanceshallbemadeany the depthrequiredshallbelargeenoughtoprovide Where sharpturnsareusedwithoutcurvedsections, freeboard incalculatingrequiredright-of-waywidths. the normaldepthofflowbeforeaddingrequired

A d 2 - d 1 =

A R V 2 2 - d ( T 1 +B dividedby2shallbeaddedto d Section A-A ) 1 / 2gR Dallas DrainageDesign Manual (Equation5.8) B T 2 ) d 2 81

SECTION 6 Drainage Storage Design

Dallas Drainage Design Manual 83 6.1 GENERAL

Stormwater detention is sometimes required to Bioretention Basins temporarily impound (detain) excess stormwater, thereby reducing peak discharge rates and velocities, as well as Bioretention is a sustainable drainage storage option providing water quality benefits. Refer to Section 2.3 for that can be used to provide water quality benefits in guidance on when detention is required. addition to detention storage. Individual bioretention areas can be used to serve highly impervious areas less The four primary types of basins or ponds are: than 2 acres in size, and typically feature a filter bed which may be tied to an underdrain and returned to the Dry Detention Basins storm drainage system. In areas with NRCS Classified A or B soils, with a low groundwater table and low risk of Dry detention basins are open space areas designed to groundwater contamination, a bioretention facility can remain dry most of the time. They fill up during large be used to infiltrate runoff directly into native soils. In storm events and drain completely through an outlet NRCS Classified C or D soils, an underlying hard-pan, structure once the storm event has passed. or rocklayer, or other impediments to percolation will Wet Detention Basins require an appropriately designed underdrain system. Section 6.9 and the methodology for bioretention outlined Wet detention basins are ponds designed to have a by the Commonwealth of Virginia may be used to develop permanent pool, sometimes with a water feature. During appropriate design. a large storm event, detention storage is provided above the normal permanent pool level; after the storm event, the Design guidance is provided for dry and wet detention detention storage drains through an outfall and the water basins (Section 6.2), retention and bioretention surface level returns to the permanent pool/normal water basins (Section 6.3), underground detention basins level. Normal ponded storage below the permanent pool (Section 6.4), stormwater ponds (Section 6.5), (dead storage) does not count towards the active detention and constructed wetlands (Section 6.6). Sediment volume. forebays are required for detention or retention basins with upstream drainage areas of 100 acres or more, Retention Basins stormwater quality ponds, and constructed wetlands. The sediment forebay should be sized to hold 0.1 inches per Retention basins are basins that do not have an outfall and impervious acre of the contributing drainage area and drain completely by infiltration into the underlying soil and should generally be 4-6 feet deep. The volume in the evaporation. During a large storm event, retention basins forebay can count towards the total design volume of the fill and provide storage. After the storm event, the water stormwater pond. A sediment marker shall be installed in drains from the site and no water is released downstream. the forebay for maintenance and upkeep. Retention basins in Dallas require analyses of site specific percolation/infiltration rates, water balance analyses, and In compliance with the current City Stormwater Permit potential underdrain design to be an effective approach in and FEMA CRS Program, water quality measures should Dallas. be incorporated wherever practicable as part of prudent and holistic drainage system design. There are several sustainable drainage measures that provide varying degrees of detention while also providing water quality benefit. Guidelines for the implementation of these measures are also provided in this section.

84 Section 6 Drainage Storage Design using theModifiedRational Method (seeSection2.3.3). and withdrainageareasof100 acresorlesscanbedesigned Detention Storage–Basinswithout upstreamdetentionareas needed, seeSections5and7). in thismanual.Ifchannelliningorenergydissipatorsare the allowedvelocityshallnotexceedvelocitiesdescribed In areasnotregulatedbytheEscarpmentRegulations, Geologically SimilarAreasbelowtheEscarpmentZone. for areasabovetheEscarpmentZoneand5ft/s flows atanonerosiverate.Thisrateisspecifiedas3 ft/s Outflow Velocity –Theoutflowstructurewilldischarge annual chancestormeventsshallbeusedfordesign. Design StormEvent–The1%,2%,10%,and50% conditions. requirements arenecessarybasedonsite-specific analysis isneededtodetermineifmorestringent development. Designershoulddetermineifageotechnical and roadways10feetfrompropertylinesforprivate detention basinsmustbesetback5feetfrombuildings must beobtained.Ataminimum,thetopofslope a USACE404permitandanyotherapplicablepermits detention pondsaretobelocatedinwatersoftheU.S., is presentwithin2feetofthebottombasin.If be locatedinareaswhereseasonalhighgroundwater Site Considerations–Drydetentionbasinsshallnot detention basinsandwetbasins. more stringentcriteria.Thesedesigncriteriaapplytodry engineer’s judgment,thepotentialhazardrequiresthese apply whererequiredbythestate,andwhere,in for damsafetyandimpoundmentofstatewatersshall established bytheStateofTexas, asregulatedbyTCEQ, for detentionbasinswithintheCityofDallas.Criteria or naturearea.Thefollowingareminimumcriteria site designandamulti-objectivefacilitysuchaspark Detention isencouragedtobeconsideredaspartof 6.2.1 DesignGuidance DETENTION BASIN 6.2 estimated bytheequation: for atrapezoidalspillwaywithcontrolsectioncanbe separate fromtheembankment,requiredwidth capacity istobeprovidedinavegetatedearthspillway structural integrityofthedamembankment.If designed topreventerosionandconsequentlossof over theembankment,spillwaywillbestructurally If theemergencyspillwaycapacityistobeprovided flood eventdoesnotovertoptheembankment. level toensurethattheundetained0.2%annualchance be providedatthemaximum1%annualchanceflood chance floodlevel.Inaddition,anemergencyspillwaywill a minimumof2.0feetabovethemaximum1%annual required detention,thetopofembankmentwillbe embankments areusedtotemporarilyimpoundthe Freeboard andEmergencySpillway–Whereearth storm rainfallunlessappropriatewaterrightsareobtained. chance stormeventmustoccurwithin48hoursafterdesign Drawdown ofthedetentionstoragefor1%annual which canbefoundontheCityofDallaswebsite. are tobeperformedusingapprovedsoftware,alistof design hydrographroutingsthroughthedetentionbasin to bedesignedusingtheUnitHydrographMethod.The where theModifiedRationalMethodisnotapplicableare Basins withdrainageareasgreaterthan100acresor The minimumcrownwidthis showninTable 6.1. for rockdamorasdetermined bygeotechnicalinvestigation. permitted foravegetatedearth embankmentis4:1and2:1 Earth EmbankmentDesign–Thesteepestsideslope the conduit. design velocitywithoutdamagetotheinteriorsurfaceof external loadorsettlement.Itmustconveywateratthe the internalhydraulicpressureswithoutleakageunder full loads withanadequatefactorofsafety. Itshallwithstand be reinforcedconcretedesignedtosupporttheexternal through theembankmentinaconduit,conduitshall of Section2.3.Wheretheoutflowstructureconveysflow encouraged asamethodformeetingtherequirements Outflow Structure–Multiple-stageoutflowstructuresare The minimumwidthforavegetatedearthspillwayis4.0feet. Z D =designdepthabovespillwaycrest(ft) Q =emergencyspillwaycapacity(cfs) Bw =bottomwidth(ft)

= sideslope,i.e.,horizontaldistanceto1footvertical(ft/ft) Bw = 0.36Q -0.7ZD ______

D 3/2 Euto 6.1) (Equation

Dallas DrainageDesign Manual 85

Maintenance Provisions – Access must be provided in detention basin design for periodic desilting and debris removal. A 12 foot maintenance access strip shall be maintained around the perimeter of any pond that will be maintained by the City. Wet detention basins must include dewatering devices to provide for maintenance.

A vehicle access ramp shall be provided if the bottom width of the detention pond is 15 feet or greater and the height of the embankment or wall is greater than 4 feet. The access ramp should be graded no steeper than 15% and be a minimum of 15 feet wide.

Fencing around detention – Security fencing with a minimum height of 4 feet shall encompass the basin area when required due to potential safety hazards created by prolonged storage of floodwater. Design shall be such as not to restrict the inflow or outfall of the basin. In basins to be used for recreation areas during dry periods, pedestrian access may be provided with the approval of the Director. Access points from streets will be controlled by a locked chain or gate.

Slope stability, erosion control, and maintenance should be considered for landscaping in detention areas. See Appendix A.6 for guidance on appropriate landscape materials for stormwater detention.

The developer will be responsible for maintenance of the basin until all construction on adjacent lots is complete (i.e., the basin is not to be used for disposal of waste building materials), required vegetation is established, and it has been accepted by the City. Maintenance deeds shall be defined on the plat.

86 Section 6 Drainage Storage Design to therequirementsdiscussedinSection6.2. proposed development,retentionpondsshallbedesigned If meetingtheneedsofrequireddetentiondueto requirements ofunderlyingsoils. needed fromtheDirector. SeeSection6.10forinfiltration site characteristicsaresuitedforretention,andapprovalis needed forproposedretentionareasconfirmingthatthe 24-hour designstorm.Adetailedgeotechnicalanalysisis to fullyinfiltraterunoffwithin48hoursfromtheendofa existing poroussoils.Retentionpondsmustbedesigned Retention pondsimpoundwaterasitinfiltratesthrough RETENTION BASIN 6.3 Section 11. underground detentionfacilitiesinaccordancewith Operation andmaintenanceplansarerequiredforall Calculations mustbeprovidedtotheCityforreview. governed bygeotechnical/structuralconsiderations. The maximumfilldepthtothetopofpipeshallbe be aminimumcoverof2feetabovethetoppipe. For undergrounddetentionpipesystems,thereshould shall befollowedifapplicable. minimum isrequired.Confinedspaceentryregulations If thevaultorpipecontainscells,oneaccesspercell Director. Covers,grates,andhatchesshallbeboltlocking. openings shallnotexceed50feetunlessapprovedbythe underground detentionfacility. Spacingbetweenaccess Maintenance accessisrequiredatbothendsofthe requirements foremergencyvehicleloading. with vehiculartraffic,thestructuraldesignmustmeet If undergrounddetentionislocatedunderneathanarea through theundergrounddetentionarea. utilities asnecessary;noundergroundshallcross unless approvedbytheDirector. Relocateunderground detention shallnotbelocatedunderneathanystructure 2 feetaboveseasonalhighgroundwater. Underground The bottomofundergrounddetentionshallbeatleast water rightsregulations. should verifythatdesigniscompliantwithallcurrent by vaults,multiplelarge-diameterpipes,etc.Designer beneficial reuse.Undergrounddetentioncanbeachieved is notfeasible,orsitesthatwishtocapturerunofffor urban development,siteswhereabove-groundstorage Underground detentionisanoptionforsiteswithdense DETENTION UNDERGROUND 6.4 6.4 Dallas DrainageDesign Manual 87

A micropool extended detention pond functions similarly If NRCS soil types A and B are present, a pond liner may to a wet extended detention pond, detaining the water be necessary to maintain a permanent pool. quality volume for 24 hours. Only a micropool remains permanently in the pond, preventing resuspension of Design Considerations sediment and clogging. If serving as required detention for To achieve efficient sediment and pollutant removal, the proposed development, refer to Section 6.2 for additional following design measures should be observed. design requirements. Stormwater pond design should include a permanent pool, Multiple pond systems can consist of several ponds, overlying zone if additional storage is desired, and a shallow storing the volume required for water quality volume and littoral zone that acts as a biological filter. Other design additional storage in two or more cells. features include an emergency spillway, maintenance If space is available, stormwater ponds can provide access, safety bench, pond buffer, and landscaping. required detention for development sites. Stormwater ponds should have a minimum length to width ratio of 1.5:1 with a permanent pool depth of 3-8 feet. Side slopes should be no steeper than 3:1. Safety benches with a maximum slope of 6% are required for any slopes steeper than 4:1.

88 Section 6 Drainage Storage Design embankment. 0.2% annualchancestormeventnotovertoppingthe designed forthe1%annualchancestormeventwith in 24hours.Embankmentandspillwaysshouldbe protection storagevolumeorextendeddetention Orifices shouldbesizedtoreleasethestreambank quality volumeandSection6.2fordetentionponddesign. water qualityvolume.SeeSection2.3.3fordesign The permanentpoolvolumecanbesizedforadesign Sizing remain freeoflargevegetation,suchasbushesandtrees. pool elevation.Thedamembankmentandspillwayareto plants should be established within 6 inches of the normal safety, wildlifehabitat,andaestheticdesign.Wetland Landscaping playsanimportantroleinpollutantremoval, and slopenogreaterthan15%. or easementandshouldhaveaminimumwidthof15feet Maintenance accessshouldbeprovidedfromapublicroad pond within48hoursunlesswaterrightsareattained. A drainmustbeprovidedthatiscapableofdrainingthe shall bemet. all detentionbasinrequirementspresentedinSection6.2 detention pondstomeettherequirementsofSection2.3, When stormwaterpondsaredesignedtoserveas should beplacedateachoutlettopreventerosion. multiple outletsatdifferentheights.Energydissipators Outlets can consist of risers, barrels, or weirs and can have forebay shouldnotbeerosive. main pond.Velocities inthe pipesorchannelsexitingthe design inflow. Theforebayshouldbeseparatedfromthe pond unlesstheinletprovideslessthan10%oftotal A sedimentforebayshouldbepresentateveryinlettothe depth of18inchesbelowthepermanentpoollevel. length of15feetandextendsintothewateratamaximum vegetation thatactsasabiologicalfilter, typicallyhasa An aquaticbench,whichprovidesashallowareafor - - - - Several differentdesignoptionsareavailable. nutrient andpollutantremovalaswellahabitatforwildlife. designed totreatandmanagestormwater. Theyprovide Constructed wetlandsareman-madewetlandsystems WETLANDS CONSTRUCTED 6.6 - - - - maintain constantaquaticlife. of 5-10acres,requiresagroundwatersupplyto A pocketwetland,whichservesadrainagearea above themarshwhichisreleasedover24hours. shallow wetlandbutalsoprovidesextendeddetention An extendeddetentionshallowwetlandissimilartoa marsh foradditionaltreatment. occurs inthewetpondbeforerunoffenters a wetpondandshallowmarsh.Sedimentation A pond/wetlandsystemconsistsoftwoseparatecells, the onlydeeperportions. shallow. Theforebayandmicropoolattheoutletare quality treatmentinthemarsharea,whichisrelatively A shallowwetlandprovidesthemajorityofwater Dallas DrainageDesign Manual 89

Pond / Wetland System A minimum of 35% of the total area should have a depth Nral Pl Eleain of 6 inches or less, and 10-20% should have a depth of 1.5-6 feet.

Pn Welan Four different zones should be present.

Extended Detention Wetland Nral Pl Eleain -- The deepwater zone should be 1.5-6 feet deep and ED ne includes the outlet micropool and deepwater channels. Ma Deenin Eleain It can support submerged or floating vegetation.

-- The low marsh zone is 6-18 inches below the normal Frea Mirl pool elevation and can support several different wetland species. Site Considerations -- The high marsh zone is from the normal pool elevation Constructed wetlands should have a minimum to 6 inches below it. It should have a higher surface contributing drainage area of 25 acres or 5 acres for area to volume ratio. It can support a greater density pocket wetlands. Constructed wetlands should not be of wetland plants compared to the low marsh zone. located on a slope greater than 8%. -- The semi-wet zone is located above the permanent Except for pocket wetlands, there should be a minimum pool and is only wet during large storm events. Plants of 2 feet between the bottom of the wetland and seasonal in this zone must be flood tolerant. high groundwater. A micropool with a depth of 4-6 feet should be designed If stormwater ponds are to be located in a navigable at the outlet to prevent resuspension of sediment. water or wetland of the U.S., a 404 permit and any other applicable permits must be obtained. No permanent pool areas should exceed a depth of 6 feet. Extended detention should not exceed a water surface At a minimum, constructed wetlands must be set elevation of 3 feet above the normal pool. back 5 feet from buildings and roadways and 10 feet from property lines. Designer should determine if a If the constructed wetland is not designed to handle the geotechnical analysis is needed to decide if more 1% annual chance storm event, a bypass system should be stringent requirements are necessary. constructed.

If soil types A and B are present, a liner may be necessary Outlets can consist of risers, barrels, or weirs and can have to maintain a permanent micropool. multiple outlets at different heights. Energy dissipators should be placed at the outlet to prevent erosion. Design Considerations An emergency spillway shall be provided that meets all The surface areas of constructed wetlands require a local and state dam safety requirements and does not space that is approximately 30% of the contributing impact downstream structures. A minimum of one foot of drainage area. freeboard must be provided from the design water surface elevation to the lowest point of the embankment. A constructed wetland should consist of a sediment forebay, a shallow marsh area with aquatic vegetation, a The designer should also review and consider inundation permanent micropool, and a detention zone to manage requirements for selected plants and perform water runoff volumes. Other design features include an balance to ensure range in water depths over wet and dry emergency spillway, maintenance access, safety bench, periods so that the design: wetland buffer, and landscaping. a) does not require make up water A sediment forebay should be provided at each inlet unless the inflow is less than 10% of the total design b) meets plant inundation requirement storm inflow. 90 Section 6 Drainage Storage Design requirements ofSection6.2 shallbemet. with therequirementsofSection 2.3,alldetentionbasin extended detentionwetlandisbeingusedtocomply for theextendeddetentionwaterqualityvolume.If the invertshouldbelocatedatmaximumelevation volume orextendeddetentionin48hours,and be sizedtoreleasethestreambankprotectionstorage For extendeddetentionshallowwetlands,orificesshould depth zonesaredefinedin Table 6.3. In addition,therecommendedratiosforsurfaceareasof Table 6.3ConstructedWetland AreaRatios Table 6.2ConstructedWetland Volume Ratios extended detentionareasasdefinedin Table 6.2. water qualityvolumesplitbetweenthemarsh,pool,and recommended thatitbedesignedbasedonthedesign to-width ratioof2:1.Forefficientpollutantremoval,itis Constructed wetlandsshouldhaveaminimumlength- Sizing detailed designguidance. Reference USACE/EPA constructedwetlandsguidancefor maximum watersurfaceelevationshouldbeprovided. main spillway. Awetlandbufferof25feetfromthe within 15feetoftheembankmentor25from and waterfowl.Wooded vegetation shouldbepresent landscaping planshouldencouragehabitatforwildlife safety, wildlifehabitat,andaestheticdesign.The Landscaping playsanimportantroleinpollutantremoval, 15 feetandslopenogreaterthan15%. road oreasementandshouldhaveaminimumwidthof Maintenance accessshouldbeprovidedfromapublic Surface Area Allocation of Allocation of High Marsh Low Marsh Deepwater Detention Semi-wet Extended V Marsh WQ in % Pool in% Wetland Wetland Shallow Shallow 75 40 25 35 20 5 0 ED Shallow ED Shallow Wetland Wetland 10 25 50 45 25 35 10 Wetland Wetland Pond/ Pond/ 30 25 70 25 45 5 0 Wetland Wetland Pocket Pocket 75 40 25 45 10 5 0 flushing, andvehiclewashing. non-potable application such as landscape irrigation, toilet non-potable waterrequirementsandcanbeusedforany for beneficialuse,reducingtheusageofpotablewater and amethodofdispersion.Rainwatercanbecaptured reuse. Thesystemcontainsadownspout,storagetank, runoff fromrooftopsinbarrelsorcisternsforbeneficial Rainwater harvestingconsistsofasystemcapturing HARVESTING RAINWATER 6.7 Figure 6.3RainwaterHarvesting Faue Hse Dallas DrainageDesign Manual Raise Base Overﬂow Sreene Inle Dnsu 91

Gutters and downspouts from the roof can easily be diverted into a rain barrel, which when placed uphill of RAIN GARDENS landscaping, can provide irrigation by gravity flow. Rain gardens are small bioretention areas that contain Design Considerations amended soil and native vegetation for receiving and Downspouts, piping, or other methods of conveyance temporarily storing stormwater runoff. Rain gardens can be can be used to runoff into storage tanks. Underground designed for full, partial, or no infiltration into underlying soil, cisterns must be designed by a licensed qualified dependent on site and soil conditions. See Section 6.10 for engineer. Design of rain barrels shall be consistent with infiltration requirements. Rain gardens provide hydrologic TAC Title 30 Part 1 Chapter 210 Subchapter F. and water quality benefits as well as aesthetic benefits.

Rain barrels should be opaque or painted if above ground Site Considerations to discourage algae growth and covered to reduce vector Due to their ability to be designed for small sites or attraction. First-flush diverters or hydrodynamic separators retrofits, rain gardens can be utilized for several different should be used to prevent contaminants from entering types of sites, including parking lot islands, roadway the supply. Leaf screens and roof washers may be desired bulb-outs, and landscaping features. They should have a to prevent debris from entering the storage tank. Storage maximum contributing area of 5 acres per treatment cell. tanks must drain within 48 hours unless a cover is Pre-treatment may be required in areas with increased provided to prevent mosquito and vector attraction. sediment, debris, and pollutants to limit maintenance For new development, roof materials may be selected needs and is required for facilities that have a contributing based on effectiveness for rainwater harvesting area of more than 2 acres. for optimization. Disinfection methods can also be implemented if potable use is desired. Backflow Design Considerations preventers are necessary to keep rainwater and municipal Rain gardens should have a ponding depth no greater than potable supply separate. Storage tanks should be located 9 inches and have a drawdown time of the full ponding at a higher elevation than desired area of use to utilize depth of less than 24 hours (3-12 hours recommended). gravity flow if possible. Pumps can be installed if needed. Rain gardens should not be built on slopes greater than 15% with side slopes of the ponded area no steeper than Overflows should be designed to divert excess rainwater 2.5H:1V unless structural walls are used. to additional storage, sustainable drainage measures, or storm drainage systems and should not discharge runoff If the native underlying soil does not have a drawdown toward structures or downstream properties. time of less than 24 hours for the entire ponding depth of the rain garden, but can still support some infiltration, a If rainwater harvesting is used for landscape irrigation, partial infiltration system can be used. In a partial infiltration the amount of supplemental irrigation necessary can be system, outflow occurs through both a raised outlet pipe significantly decreased. and infiltration into underlying soil. If the native soil supports The following equation can be used to determine rain a drawdown time of less than 24 hours for the full ponding barrel volume. depth, a full infiltration rain garden can be used. Otherwise, V = A * R * 1 ft/12 in * 0.90 * 7.5 gal / ft3 an underdrain must be installed that can convey the full design water quality volume. Underdrains are required (Equation 6.2) when clay or geomembrane liners are used to protect V = volume of rain barrel (gal) infrastructure or utilities, or if the soils do not allow infiltration. A = surface area of roof (ft2) Runoff may enter the rain garden through sheet flow, curb R = rainfall (in) cuts, curb cut forebays, or inlets. Where sheet flow enters 0.90 = system efficiency the rain garden, a maximum side slope of 4:1 shall be used. 92 Section 6 Drainage Storage Design set ofequations isfordeterminingthefiltration areaof rain gardensand contributingdrainageareas. Thefirst The following section containstwomethods forsizing Sizing maintenance usingstandard equipment. Rain gardensmustbeaccessible fromtheright-of-wayfor dependent onsiteconditions. ROW. Theymaybenecessaryfornoinfiltrationsystems a raingardenislocatedwithin10feetofbuildingor Impermeable orlowpermeabilitylinersarerequiredif course underneaththeraingardenorbioretentionsoilmix. Additional storagecanbeprovidedbyagravelreservoir infiltration andtopreventclogging. be placedatleast6inchesabovebottomforincidental have aninfiltrationrateof50in/hr. Underdrainshall should beplacedtoaminimumdepthof18inchesand subbase soil,gravelstoragereservoir, orunderdrainand Bioretention soilmix(BSM)shallbeinstalledoverthe the existingsubbase. underdrain isrequired,thenthemixmaybestratifiedinto shall beinstalledovertheripped/tilledsubbasesoil.Ifno garden. Raingardenplantingsoilmixoramendments Wood mulchshallbeappliedtothesurfaceofrain materials intoguttersorontoadjacentpavementsurfaces. through theraingardenandwashmulch,soils,plant whereas, on-lineopeningsmaycausemajorerosion prevent erosionandscouringimpacttoaraingarden; and thenbypasstothestorminlet.Off-linecurbopenings runoff toenterthepondingareaofraingardenuntilfull cuts oropeningsatthelowsideofraingardentoallow Overflow bypasscanbeprovidedbyusingoff-linecurb chance 24-hrstormevent. events. Theoverflowshallbesizedforthe1%annual the capacityofdischargesystemduringlargestorm Backwater calculationsmayberequireddependingon waters, publicstormdrainsystems,orstoragereservoirs. the maximumpondingelevationswhichleadtosurface pipes, horizontaldrainageorarmoredchannelsat Overflow canbeprovidedbyadjacentinlets,verticalstand establish preferentialflowtotheraingarden. overflow inletnexttoaraingarden,gradesshouldbeset outflow velocitiesshallnotexceed2ft/s.Whenplacingan once themaximumpondingdepthisreached.Inflowand An overflowoutletshallbeprovidedforrunofftobypass maximize waterqualitybenefitsandreduceerosiveeffects. without theretentiontimeinsystemforinfiltration,to circuiting, whenflowtravelsstraightfrominflowtooutflow and outflowlocationsshouldbedesignedtopreventshort- adjacent to the rain garden can slow inflow velocities. Inflow needed forpointconcentratedinflows.Grassfilterstrips entering thesystem.Energydissipatorsorforebaysmaybe Method ofinflowshouldpreventleavesanddebrisfrom n H =maximumheadoverthebioretentionsoilmix(ft) V d d n H =maximumheadoverthegrowingmedium(ft) (See Section2.3.3) D n a designwaterqualityprecipitation(P use thedesignwaterqualityvolumeassociatedwith rain gardenthatwillstillprovidewaterqualitybenefits, the maximumallowablecontributingdrainageareatoa garden andtreatadesignwaterqualityvolume.To find contributing drainageareathatcanberoutedtoarain The followingequationcanbeusedtodeterminethe Garden SizeandDesignWater QualityVolume: Sizing ContributingDrainageAreaBasedonKnownRain n A determined usingthefollowingequation. of theraingardenbasinabovesoilmix,canbe The filtrationarearequired,thesurfaceatbottom Drainage AreaandDesignWater QualityVolume: Rain GardenSizingBasedonKnownContributing system, pre-approvalmustbegivenbytheDirector. required raingardenareaforapartialorfullinfiltration infiltration attheprojectsitethatwouldresultinasmaller benefits. Ifthedesignercandemonstratesignificant of runofftreatedthatwouldstillresultinwaterquality precipitation of1inchischosenastheminimumamount area foraknowndrainagearea.Adesignwaterquality determines themaximumallowablecontributingdrainage and aspecifiedwaterqualityvolume.Thesecondset the raingardenbasedonaknowncontributingarea A A provide increasedwaterqualitybenefits. rainfall. Agreaterdesignwaterqualityprecipitationwill d d 2 2 1 1 A 2 1 2 1 max WQ f f WQ =filtrationarea(ft =filtrationarea(ft

=depthofthegravelreservoir course(ft) =depthofthebioretentionsoil mix(ft) =depthofthegravelreservoircourse(ft) =depthofthebioretentionsoilmix(ft) = = = = A f

effectiveporosityofthegravel reservoircourse(typ.0.35) effectiveporosityofthegravelreservoircourse(typ.0.35) effectiveporosityofbioretentionsoilmix(typ.0.30) effectiveporosityofbioretentionsoilmix(typ.0.30)

= max = designwater quality capturedepth(in) = V = contributing drainage area for specified rain garden (ft designwaterqualityvolume(ft = WQ 12*A ______ / ( H f (H+n + D 2 2 n ) ) WQ

1 d * 1 *d

1 1 + +n (Equation6.4) n 2 2 d * *d Dallas DrainageDesign Manual 2 2

) Euto 6.3) (Equation ) WQ ) (SeeSection2.3.3)

) of1inch 2 93 )

Flow–through planters can receive runoff from roofs and residential, commercial, and mixed-use sites. Infiltration planters can also receive runoff from roadways, parking lots, and other paved surfaces.

94 Section 6 Drainage Storage Design Conservation ServiceSoilSurvey (NRCS.) the U.S.DepartmentofAgriculture NationalResources determined basedonlocation andsoiltypeusingdatafrom the feasibilityofinfiltration. Hydraulic conductivitycanbe and otheravailabledatashouldbeutilizedtodetermine Resources suchassoilsurveymaps,reports,geotechnical, Desktop Study described abovetopreventpondingandclogging. underdrain mustmeetthesamedesigninfiltrationrateas Media usedinsustainabledrainagemeasuresincluding into nativeunderlyingsoilsisproposed. standard testmethodsmustbeperformedifinfiltration hydraulic conductivitymethodsusingappropriateASTM left tothediscretionofDesigner. In-situtestingusing Methods fordesktopstudyandfieldsamplingshallbe appropriate underfilterdesign. Commonwealth ofVirginiamaybeusedtodevelop must beinstalled.Themethodologyoutlinedbythe requirements arenotmetforinfiltration,anunderdrain rate usingthemethodsdescribedinthissection.Ifthese of 0.5tothemeasuredsteadystatesaturatedinfiltration infiltration rateshouldbedeterminedbyapplyingafactor must bebetween0.5–3inchesperhour. Thedesign into nativeunderlyingsoils,thedesigninfiltrationrate For sustainabledrainagemeasuresthatuseinfiltration considerations foryourparticularlocation. of thedesignprocesstodetermineappropriate and geotechnicaltestingshouldbeimplementedasapart FEMA regulatoryrequirements.Appropriategeochemical relative tocompliancewithcurrentUSEPA, TCEQand design cannotbeconsidered,anditisencouraged There isnoplaceinDallaswheresustainabledrainage TESTING REQUIREMENTS AND INFILTRATION 6.10 be provided. the proposedmeasure.Ifnot,anunderdrainsystemmust Determine iftheobservedinfiltrationrateisacceptablefor verification testing. are othersiteconditionsofconcern,theCitymayrequire facilities are serving an area greater than one acre or there should beadjustedinthefieldasnecessary. Ifinfiltration of thewaterqualitycontrol,buttestlocationanddepths conducted asclosepossibletothebottomelevation one testper2,000squarefeet.Infiltrationtestsshouldbe Tests shouldbecarriedoutwithafrequencyofatleast testing methodsshallbeusedbelowthewatertable. methods shallbeusedabovethewatertableandslug supervision ofaqualifiedprofessional.Infiltrationtesting capacity ofthesoilandshouldbedoneunder methods areavailablefordeterminingtheinfiltration most accurateinfiltrationrate.Severalin-situtesting In-situ infiltrationorpercolationtestingwillprovidethe In-situ Testing analyzed todetermineaninfiltrationrateforthesite. be collectedatthedepthofexpectedinfiltrationand and correspondingrequirements.Soilsamplesshould depth requiredforthesustainabledrainagemeasure 500 square feet.Test holesmustextendtotheminimum be carriedoutwithafrequencyofatleastonetestper Test pits,probes,borings,orsimilarmethodsshould be doneunderthesupervisionofaqualifiedprofessional. conditions attheproposedprojectlocationandshould Field samplingisdonetodeterminedepthandsoil Field Sampling more stringentrequirementsarenecessary. determine ifageotechnicalanalysisisneededtodecide if to preventadverseeffectsfrominfiltration.Designershould back a minimum of 5 feet from buildings and property lines requirements asstatedinthissectionandmustbeset infiltration systemsareused,theymustmeetthe soil orgroundwatercontamination.Whenfullpartial growing mediumorwhereinfiltrationwouldcontributeto of historicalhighgroundwaterfromthebottom measures arenotpermittedinareasthatwithin2 feet loadings. Fullorpartialinfiltrationsustainabledrainage areas withindustrialorhazardousrunoffhighsediment Sustainable drainagemeasuresshallnotbeplacedin Dallas DrainageDesign Manual 95

The design guidance in this section is intended for stormwater pump stations only. The City of Dallas has 6.11.1 Design Guidance a larger interior drainage system that utilizes sump lift Refer to FHWA Hydraulic Engineering Circular No. 24 stations. A pre-development meeting is required for (HEC-24), TxDOT Hydraulic Manual, and Hydraulic projects relating to the city-wide interior drainage system, Institute standards for design and specifications of a and for projects that require pump stations. pump station. The pump station or pump wet well should be protected with fences, gates, and locks to prevent illegal entry. Adequate 6.11.1.1 Pump Station Hydrology access should be available for service and maintenance In order to design a pump station effectively, the inflow vehicles during a storm event. Standard OSHA rules and hydrology must be known. The hydrology developed other industrial standards of safety shall be followed for for the associated storm drain system usually will not installation as well as maintenance of a pump station. serve as a firm basis for discharge determination into Figure 6.4 Sump Area with Drywell the pump station. A hydrograph is required because the time component is critical in understanding the inflow Ouall which governs the sizing of the wet well. The designer needs to know not only the peak inflow, but the timing Disarge B and volume. The difference between the input and the output hydrographs is the storage requirements of the Disarge Pie pump station wet well. The hydrograph should consider the storage abilities of the storm drain system, which may Dr Well reduce the required size of the wet well. Governmental regulations or the physical limitations of the receiving waters Pu We Well determine the output discharge from the pump station. Mr The design frequency for a pump station will be the 1% annual chance storm event.

A mass inflow curve represents the cumulative inflow Suin Pie Su Frea volume with respect to time. In order to determine a mass inflow curve, the hydraulic designer must first develop an inflow hydrograph based on a design storm. The most

96 Section 6 Drainage Storage Design Figure 6.6Typical CrossSection a largerwetwellvolume. the allowabledischargeisfinebutlowerraterequires same dischargerating.Aslightlylowerpumpratethan necessary. Abackuppumpisrequired,andwillbeofthe and whetherasingleornumberofpumpswouldbe be madeusingseveralmanufacturers’technicaldata economic analysisbythedesigner. Adecisionmust for thefacility. However, pumpselectionisamatterof determines thenumberandsizeofpumpsrequired The selectedrateofdischargefromthepumpstation significant storagecapacity. drain system.Thestormsystemcanrepresenta pipes, boxes,inlets,manholes,andditchesofthestorm of theavailablestoragevolume.Theseincludesumps, water beforefloodingoccurscanalsobeconsideredpart Other spacesoutsideofthewetwellwhichstorestorm drops totheminimumwaterlevel. maximum waterlevel,andisstoppedwhenthe storage volume.Pumpingisinitiatedatorbelowthe the maximumwaterlevelisnotincludedincalculated should notbeallowedtoexceed.Anyfreeboardabove water level,thelevelinwetwellabovewhich The topofthestoragevolumedeterminesmaximum sedimentation andheavytrashthatwashintothesystem. sump mustalsohaveroombelowthepumpintakelevelfor pump fromattemptingtodryorsuckingair. The must maintainwaterabovethepumpinlettokeep level, whichisthepumpcutoffelevation.Thewetwell volume ofthewetwellbelowrequiredminimumwater be madeforasumpandfreeboard.Theisthe total volumeofthewetwellbecauseallowancesshould The storagevolumeofthewetwellshouldbelessthan 6.11.1.2 PumpStationHydraulics Hydraulic EngineeringCircularNo.24(HEC-24). Hydrograph andtheprocedurecanbefoundinFHWA typical designmethodistheNRCSDimensionlessUnit Eleain 1104 Disarge Prse Su Eleain 914 Cu Eleain 10000 MA HW 31 1 Tan 10000 Eleain Greaer 31 pump station. to theowneruponcompletionandacceptanceof manuals shouldbeprovidedbythecontractororengineer All semantics,productinformation,andoperational conditions, especiallyairquality. pump station,includingmonitoringofenvironmental measures tobetakenpriorandduringanyvisitthe procedures forthepumpstation.Theplanshouldidentify be developedaspartoftheoperationandmaintenance requirements mustbeadheredto.Anentryplanshould During pumpstationoperation,allOSHAandlocalsafety 6.11.1.3 OperationandMaintenance considerations. final designandpumpselectionmustbebasedonall this stageofthedesigninselectingrightpumps.The or technicalrepresentativecanbeinvaluablesourcesat pumps. Manufacturer’s printedtechnicaldataandasales pumps alsooffertheopportunityforastaggeredstartupof recommended forreliabilityandmaintenance.Multiple necessary, aminimumoftwosmallerpumpsis one pumpmaybeabletosupplytheentiredischarge alternative toalargerwetwell.Insituationswhere wet wellandusingfewerpumpsmightbeareasonable and physicalrestrictionsforthewetwell.Enlarging The designermustalsoconsiderthecostofconstruction operating efficiencyofthepumpingstation. should beperiodicallyperformedtocheckthecontinued causes, andsolutionsavailable.Afullperformancetest Circular No.24(HEC-24)hasagenerallistofproblems, unforeseen circumstances.FHWA HydraulicEngineering to failureorreduceddurabilityofthepumpduepossible be addedforfuturepumpmaintenanceand/orremovaldue in pumpefficiencyandpossiblefailure.Aprovisionshould sediment removal,asthebuild-upmaycauseareduction frequency ofinspectioninregardstotheneedfordebrisand An operationandmaintenancescheduleshouldidentifythe 31 L PinDiInle Sr DrainClleinPie 1 31 Inle Dallas DrainageDesign Manual 97

SECTION 7 Erosion and Sediment Control Measures

Dallas Drainage Design Manual 99 7.1 7.2 GENERAL NATURAL CHANNEL

All projects shall be designed so that erosion is minimized SETBACK during construction as well as after the construction is completed. The volume, rate and quality of storm water Natural channel setbacks are delineated buffers around runoff originating from development must be controlled natural channels in which no development can occur. to prevent soil erosion. Specific efforts shall be made to The setback prevents damage from large flood events and keep sediment out of street and water courses. BMPs preserves natural riparian habitats. (best management practices) for construction should be coordinated with permanent erosion control measures. The natural channel setback shall be included in the Drainage Easement for the channel. Creek bank erosion and sedimentation are natural processes, but can be aggravated by human causes. The natural channel setback shall be computed by each of Erosion is typically a concern along the outside curves for the two following methods. The method that results in the curved channel banks, and areas located within the Dallas larger setback shall be used to define the minimum natural escarpment and geologically similar areas (the Dallas channel setback. See Figure 7.1 for an illustration of the two escarpment areas are shown on the City of Dallas Zoning methods. For the purpose of defining the natural channel website). Typically, soils that are not protected by vegetation setback, the following terms & definitions shall apply. or armoring are more susceptible to erosion processes. As a result, sediment can be carried and deposited in a Crest means the line at the top of the bank where the stream, and may have negative impacts on aquatic life. channel slope becomes flatter than four to one. Toe Severe erosion can also lead to bank failure, which can be means the line at the bottom of the bank where the slope caused by removal of vegetation or alteration of the creek becomes steeper than four to one. channel. Whenever possible, vegetated buffer zones shall be used between developed areas and creeks. Barren Method 1 slopes or disturbed areas of creeks shall be stabilized and A line that is formed by the intersection of the surface revegetated. Planted erosion control mats or other slope of the land and the vertical plane located a horizontal stabilization methods shall be used on earthen slopes distance of 20 feet beyond the crest. steeper than 2:1 or in areas of high velocities. Method 2 A line formed by the intersection of the surface of the land beyond the crest and a four to one sloping plane for clay or shale soils that begins at the horizontal location of the toe, but at an elevation equal to the flowline of the stream. For other soils, a three to one sloping plane can be used.

100 Section 7 Erosion & Sediment Control Measures Figure 7.1NaturalChannelSetback Permit 150000. construction, refertoTPDESGeneralConstruction For additionalrequirementsfornaturalbufferduring area canhelptomaintainthesenaturalbuffers. Establishing, andmaintainingprojectsetbackswithinthis - - following scenarios: may beapprovedbytheDirectorundereitherof Establishment ofasmallernaturalchannelsetback - - Me 2 smaller setback. a professionalengineerprovidingjustificationfor A geomorphicassessmentispreparedandsealedby to preventerosionofthechannelslope. A structurallyengineeredretentionsystemisdesigned Me 1 41 rSeeer Sea Le T Ban 4 le 20 1 Naural CannelSea Uliae BWi Hrinal Lii Buil W ex 1 Right Top ofBank(Low Bank) Me 2 Sea 4 Assuing ClarSaleSils 41 rSeeer 20 rig Me1 Dallas DrainageDesign Manual Flowline Te Cres 101

Where an NPDES (National Pollutant Discharge Elimination System) Construction General Permit is 7.4.1 Grass / Vegetation required for construction of a project (under regulations Vegetation in channels should have grasses as described contained in 30 TAC, under the authority of the Clean in Appendix A.6 with a good, deep root structure to Water Act), a Storm Water Pollution Prevention Plan stabilize the soil from erosive velocities. (SWPPP) meeting the permit requirements must be prepared, included with the plans and specifications, and posted onsite during construction. 7.4.2 Turf Reinforcement SWPPP must be prepared and implemented on the site There are a number of turf reinforcement mats (TRM) before any construction activities begin, including grading, and high performance turf reinforcement mats (HPTRM) and must be continuously updated. that are available to the design engineer. Selection and installation of the TRM or HPTRM is critical to the In addition, all projects shall comply with the stability of the earthen channel. The TRM will provide requirements for storm water management at construction scour protection and enhance the vegetative root and sites as set forth in the Construction General Permit, stem development. Design aids for the design of TRM TXR150000 as well as Texas Water Code Chapter 26 and and HPTRM can be found in FHWA HEC-15, Design of TAC Chapter 30. Construction plans and specifications Roadside Channels with Flexible Linings. must include the types of management, structural, and source control measures, known as BMPs. 7.4.3 Bioengineering Technical guidance for the preparation of a Storm Water Pollution Prevention Plan and implementation of BMPs Bioengineering methods can be used instead of rock for construction sites may be referenced in the iSWM armoring structural methods in appropriate scenarios. Construction Controls Technical Manual. While bioengineering techniques may be cheaper than other methods, they should only be used in The owner and operator are responsible for maintenance channels where the methods can withstand high-flow of erosion and sedimentation control measures and must velocities. Many bioengineering methods can be used remove sediment resulting from construction from City in combination with, or in addition to hard armoring. right-of-way or storm drainage systems. Designers are encouraged to reference the NRCS publication NEH-634, “Stream Restoration Design” for detailed discussions of bioengineering design methods. Several bioengineering options are presented in Figure 7.2.

102 Section 7 Erosion & Sediment Control Measures Figure 7.3LiveCribwalls Figure 7.2Bioengineering lal suranlngeregraain De asreuirereagains Sreae Base Flow Forming Flow Cannel Sreae Baseﬂow Stream-Forming Flow W ire SeureSaes Geeile Fari Dea SuSae Sle Te

2 Lie Sae Brus Maress a alseesirale Lie saingrira 4 6 Lie BranCuings Lie &DeaSuSaeSaing Lie FasineBunle 2 N allesuseuseininain Ea WaMiniuLeng25 Dea SuSaeDrienn2Ceners Lie Sae R Fill Maerial Cae Fill Dallas DrainageDesign Manual 16 GaugeMes Ersin CnrlFari Bran Cuing 103

Brush Layering high-turbulence areas. The equation calculates D30, the stone size for which 30% of the stone mix is finer than Brush layering consists of creating a series of benches by weight. is typically 15 percent smaller than . with live branches covered with soil and compacted. The D30 D50 shall lie between and . The equation to branches stabilize the slope, especially as they take root D85 1.8D15 4.6D15 determine is as follows: and grow. The edges of the branches that stick out of the D30 slope help reduce surface erosion. γ 0.5 2.5 D = FS C C C d ___w ____V 30 s v T [ ] (γs- γ w) ( ) Brush Mattressing √K1 gd In brush mattressing, a mattress-like branch layer is (Equation 7.1) secured to the surface of the bank to reduce erosion. stone size (ft); percent finer by weight Dm = Live Cribwalls FS = factor of safety (usually 1.1 to 1.5), suggest 1.2 A live cribwall is built using logs or timber tied with live stability coefficient for 2:1 slope or flatter , branch cuttings. See Figure 7.3. They can be used for Cs = C = 0.3 slope protection either along the streambank or at the toe (0.3 for angular rock, 0.375 for rounded rock) of the slope. Cv = velocity distribution coefficient (1.0 for straight Geogrids channels or inside of bends, calculate as below for outside of bends) Geogrids are geotextiles wrapped around lifts of soil and compacted to provide structural stability and protection CT = thickness coefficient (use 1.0 for or 1.5 , whichever is greater) against erosion. Materials range from plastics to natural D100 D50 geotextile such as coir. d = water depth (ft) Figure 7.4 Geogrid specific weight of water (62.4 lb/ft3) Yw = specific weight of stone (lb/ft3) Ys = local velocity; if unknown use 1.5 V = Vaverage Hig sreng geeile r gegri side slope correction as computed in Equation 7.3 K1 = g = acceleration due to gravity = 32.2 ft/s2

104 Section 7 Erosion & Sediment Control Measures may damageordislodgetheriprap. shall beclearofobstructions,debris,andtreerootsthat the underlyingmaterial.Theareawhereriprapisplaced erosion ormigrationofbankmaterialandundermining bed shallbeplacedunderneaththeripraptoprevent the subgradeunprotected.Ageotechnicalfabricorfilter stone sizesarenotsegregatedtopreventvoidsthatleave size. Stonesshallbeplacedusingamethodwherethe Design methodologyandguidance forgabionproducts gabions topreventstructural damagetothebaskets. woody vegetationshallnotbe allowedtogrowwithinthe While vegetationcangrowwithin thebaskets,large that isgalvanizedorcoated in plastictopreventcorrosion. The basketsaremadefromweldedorwovenwiremesh structures, orprotectotherareaswitherosivevelocities. also beusedtoconstructdropstructures,pipeoutlet mattresses arenotadequatetostabilizeslopesandcan Gabion basketscanbeusedtostabilizeslopeswhere the bedorbanksofastreamagainsterosion. Gabion mattressesareshallowandcanbeusedtoprotect anchoring andtoedownsarerequired. installed perthemanufacturer’s instructionsand proper soil frommigratingintothegabions.Thegabionsshallbe the basketormattressisrequiredtokeepsubgrade of rocksareasmallerdiameter. Afilterblanketbelow can beusedsimilartorockriprap,butusuallythesize Gabions are rock filled wire baskets or mattresses. Gabions 7.4.5 Gabions Minimum riprapbedthicknessshallbe1.5timestheD Angular stoneshallbeusedtopromoteinterlocking. effectiveness aterosionpreventionasthecorrectsizing. The properplacementofriprapisjustasimportantfor ϕ =angleofrepose(typically40˚) θ =angleofrockfromthehorizontal The sideslopecorrectioncanbecalculated: W =watersurfacewidth(ft) R =centerlinebendradius correction canbecalculated: The outsidebendvelocitycoefficientandthesideslope (equation onlyapplicableforanglesofrock C v = K smaller thantherepose angle) 1 1.283 -0.2log = √ ______

1 - sin sin ___ 2 2 ϕ θ

(

(Equation7.3) W __

) (Equation7.2) 50

for designinformation. slopes withafilterlayer. Refertomanufacturerguidelines do notactasretainingwallsandmustbeplacedonstable system andcanallowforvegetation.Concreteblockmats hard armoring,theyalsoallowfordrainagethroughthe and minorchangesinthebankgeometry. Whileproviding erosion control.Theyallowforflexibility, quickinstallation, uniform concreteblocksthatcanbeusedforhardarmor Concrete blockmatsareflexible,interlockingsystemsof 7.4.7 ConcreteBlockMats for erosivevelocities,orconfinedchannelareas. The liningofachannelwithconcretemaybenecessary 7.4.6 Concrete with FlexibleLinings. be foundinFHWA HEC-15,DesignofRoadsideChannels the designofgabionmattressesandbasketscan are availablefrommostmanufacturers.Designaidsfor 6. 5. 4. 3. 2. 1. parameters/criteria: Retaining walldesignshallconsiderthefollowing sliding, unlessotherwiseapprovedbytheDirector. factor ofsafety2againstoverturningand1.5 Retaining wallsshallbedesignedtoachieveaminimum Details, shallbesubmittedwithsupportingcalculations. modifications ofthe251D-1StandardConstruction by theDirector. Specialstructuraldesigns,including designed forthespecificonsiteconditionsandapproved annual chancefloodplainintheCityofDallasshallbe All retainingstructures/wallslocatedwithina1% refer toSection4oftheStreetDesignManual. environment. Forretainingwallsinotherenvironments, This sectiondiscussesonlyretainingwallswithinacreek 7.4.8 RetainingWallsinWaterways pressures shouldbeconsidered) and thesubsequentdecrease inpassiveresistance deterioration ofmaterialsat the toeofstructure, Resistance tosliding(Thepotential forfuture Uplift ifapplicable Backfill drainage(perforatedpipeorweepholes) irrigation, etc. Hydrostatic pressureduetostormwater, groundwater, Surcharge loadings,existingandfuture Allowable soiland/orrockbearingcapacity Dallas DrainageDesign Manual 105

8. Erosion at the ends of the wall over top of wall and undermining at the toe

9. Adequate room or right-of-way for construction of the footing

10. Placement of construction and expansion joints

11. Potential for impact or abrasion (Gabions and similar materials should be avoided in areas subject to direct impact from debris or falling water)

12. Maintenance requirements

13. Lateral loads due to onsite material or select fill

14. Proper compaction of backfill

15. Sustained velocity and shear stress

Base layers of gabions should be placed below expected scour depth. If retaining wall does not extend above the expected water surface elevation for the design flood, measures such as tiebacks to protect against flanking should be installed.

Any wall taller than 4 feet in height will require a building permit and an engineer’s certification that the wall is structurally sound and built as per plan specifications. Any wall taller than 6 feet in height must comply with OSHA requirements during construction and future maintenance. Any retaining wall that extends beyond the natural creek bank, blocking the natural flow of water in any way, must be analyzed hydraulically per Article V Section 51A-5.100-5.105 to verify it has no impact.

106 Section 7 Erosion & Sediment Control Measures Dallas DrainageDesign Manual 107

SECTION 8 Floodplain and Sump Design Requirements

Dallas Drainage Design Manual 109 8.1 8.2 GENERAL FLOODPLAIN

Development within floodplain or sump areas requires HYDRAULIC ANALYSIS special consideration. The City of Dallas is susceptible to flooding and has regulations in place to minimize loss Development within or adjacent to a floodplain must of life and property. Increasing development throughout comply with the floodplain regulations, Article V, Section the City and within the floodplain areas can lead to 51A-5.100-5.105, and coordinate with the appropriate increased runoff and flooding. No development may occur regulatory agencies. A floodplain / floodway study must be that raises flood water levels within floodplain areas or completed if a project site is in or adjacent to a mapped adversely impacts runoff storage capacity. Valley storage floodplain area to determine that there is no negative requirements in Article V, Section 51A-5.100 shall be met. impact from development. Major floodplain / floodway Special consideration should be given to ensure that there studies must conform to FEMA regulations described in is no increase in water surface elevation within a project, Part 65 of 44 Code of Federal Regulations, and the City of upstream or downstream. Dallas Development Code.

The designer is responsible for the collection of all existing data with regard to flooding in the study area. This search could include published reports, specific information on past flooding, drainage structures in the area, available topographic maps, available Flood Insurance Rate Maps (FIRM), and photographs of past flood events.

If the floodplain is impacted by encroaching development, proposed floodplain exhibits should include (but not be limited to):

-- Existing and proposed contours

-- Location, size, and elevations of proposed structures

-- Filled and excavated areas with proposed contours and grades

-- Location and elevation of roads & utility lines

-- Existing and proposed floodplain boundaries

-- Cross-section locations

-- Property boundaries

-- Survey information, including benchmarks and control points

110 Section 8 Floodplain & Sump Design Requirements 1

See Article V Sections 51A-5.100-5.105 of the Dallas 8.2.1.3 2D Unsteady Flow Modeling INTRODUCTION Development Code and Procedures for Filling in a Floodplain Under the Flood Plain Management Guidelines for additional 2D unsteady flow modeling eliminates the assumption 2 floodplain regulations. that velocity is one-dimensional. Rather than using a cross-section to estimate one-dimensional velocity HYDROLOGY perpendicular to the cross-section, the terrain is 8.2.1 Hydraulic Modeling subdivided into a grid, where depth and velocity are Floodplains and floodways should be modeled using computed for each grid element across the terrain. Velocity in any horizontal direction is thus accounted 3

approved software, a list of which can be found on the ROADWAY for in 2D modeling and the water surface elevation is City of Dallas website. Further explanation of the different DRAINAGE DESIGN types of modeling techniques and appropriate uses can not assumed to be constant across a floodplain. 2D be found in the HEC-RAS Hydraulic Reference Manual. unsteady flow modeling is often used where significant flow is expected to occur that would not be perpendicular

Cross sections used in the hydraulic analysis shall to a traditional 1D cross-section. Examples of such 4 be representative of current channel and floodplain instances are wide floodplains, roadway crossings with BRIDGE conditions obtained by surveying. When cross section data multiple opening bridges, or other floodplain obstructions HYDRAULIC DESIGN is obtained from other studies, the data shall be confirmed that invalidate an assumption of one-dimensional flow. to represent current channel and floodplain conditions, or Another common application is the modeling of shallow

new channel cross section data shall be obtained by field floodplains in urban settings where it is desirable to 5 survey. All information should be referenced directly to understand the path, depth, velocities, and timing of DESIGN the most updated vertical datum. If other datum was used runoff that traverses through urban areas. OPEN CHANNEL for the source data, conversion information is available through the National Geodetic Survey. While 2D unsteady flow modeling can require more effort than 1D modeling, the 2D modeling can often provide

additional information and a more detailed understanding 6 8.2.1.1 1D Steady Flow Modeling of flooding conditions. In previously developed areas DRAINAGE STORAGE DESIGN 1D steady flow modeling can be used when flow is where an undersized storm system results in localized steady, gradually varied, one-dimensional, and the slope flooding, a 2D unsteady model can aid assessment of the river is less than 1:10. 1D flow assumes that the of potential downstream impacts that may result from velocity components are only in the direction of flow; that upgrading a system to eliminate the localized flooding 7 all flow is perpendicular to the modeled cross-sections. and the existing storage associated with the inundated Velocity in directions other than the direction of flow are areas. For more guidance on 2D modeling, reference CONTROL MEASURES EROSION & SEDIMENT not accounted for. Steady flow modeling assumes that the HEC‑RAS River Analysis System 2D Modeling User’s conditions at a given point in the stream remain constant Manual (Version 5.0 February 2016 or latest version) or with respect to time. Steady flow modeling should not be other approved software reference manuals. used when flow is significantly influenced by other factors,

such as dam breaching, levee overtopping, flow reversals, 8 or very flat areas where significant floodplain storage may impact flow. FLOODPLAIN & SUMP DESIGN REQUIREMENTS 8.2.1.2 1D Unsteady Flow Modeling 1D unsteady flow modeling allows the user to model the change of depth over time during a storm event as 9 discharge increases and then recedes. The assumption REQUIREMENTS of one dimensional velocity is maintained. 1D unsteady OTHER REGULATORY flow modeling is often utilized where significant floodplain storage is expected to have an impact on modeling results. In an unsteady flow model, an upstream boundary condition is required where a flow hydrograph for the 10 SUBMITTAL SUBMITTAL reach is applied. REQUIREMENTS 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 111 APPENDICES 8.3 8.4 REGULATORY FLOODPLAIN FLOODPLAIN MAPS APPROVAL PROCESS

Floodplain maps may be found through FEMA, but If a project is within 100 feet of a stream, the designer coordination is required with the Director to ensure that shall check with the City to determine whether the project the latest updated floodplain maps are used for design. is impacted by a floodplain.

A fill permit shall be used to remove an area from a designated floodplain. A floodplain alteration permit shall be used when there is alteration on the site, but it is not removed from the floodplain. Fill or floodplain alteration permits are pre-cursors to a building permit. Work may not begin after the approval of a fill or floodplain permit until all other building permits are approved.

If storage is provided to offset fill in accordance with Article V Section 51A-5.100-5.105, it must be within property boundaries. City right-of-way or easements shall not be used for storage requirements.

The following sections shall be met for both fill and floodplain alteration permits as per the current floodplain regulations at the time of the adoption of this manual. 8.4.1 Fill Permits Fill is prohibited within a floodplain unless it is demonstrated that all criteria are met and a fill permit is approved. If a fill permit is approved, property can be developed to a specified elevation. Refer to Article V Section 51A-5.100-5.105 of the Dallas Development Code for guidance on regulations and permitting within floodplains. A FEMA Letter of Map Revision is needed to re-designate an area that was previously in the floodplain. A Corridor Development Certificate (CDC) may be needed before a fill permit can be approved if located within the Trinity River Corridor.

112 Section 8 Floodplain & Sump Design Requirements 1

Building pads must be a minimum of two feet and the INTRODUCTION finished floor a minimum of three feet above the design flood elevation. The water surface elevation of a creek or river may not be increased upstream, downstream, or 2 throughout the project unless in a detention area. Post- HYDROLOGY project velocities downstream, if above 6 ft/s, shall not exceed existing velocities. 3

8.4.2 Sump Fill Permits 8.5 ROADWAY DRAINAGE DESIGN A fill activity within a sump area requires a fill permit, using the method outlined herein, consistent with the Floodplain Ordinance. If fill action for a project is located ENHANCEMENTS AND within the critical zone for a levee system (see Figure 4 8.1), it will require a fill permit. In addition, the following RECREATIONAL USES BRIDGE items shall be reviewed for applicability: ROW/easement HYDRAULIC DESIGN abandonment, 404 and 408 permitting (See Section Multi-purpose detention areas can be sized to temporarily 9.2), and USACE Section 10 Harbors Act approval. All store a portion or all of the volume of runoff required floodplain permits require an application meeting to to control the flood mitigation storm, if required. Multi- 5 support full understanding of project requirements. DESIGN

purpose areas should not be used for extended detention OPEN CHANNEL or water quality treatment. Routing calculations must be 8.4.3 Floodplain Alteration Permits used to demonstrate that the storage volume is adequate. See Section 6 for detention storage design. Emergency

A floodplain alteration is defined as “the construction overflows are to be provided for storm events larger than 6 of buildings or other structures, alterations, mining, the design storm. The overflow must have no adverse DRAINAGE dredging, filling, grading, or excavation in the floodplain impact to downstream properties or the conveyance STORAGE DESIGN which does not remove a floodplain designation.” system. Damage of property and conveyance systems Floodplain alteration permits are needed for structures should be minimized. Maintenance plans after flooding such as swimming pools, tennis courts, fences, and events are required. significant landscaping that lie within a floodplain. A 7 Corridor Development Certificate (CDC) may be needed Parks, sports fields, etc. may be built within the CONTROL MEASURES before a floodplain alteration can be approved if located floodplain if a floodplain alteration permit is approved, EROSION & SEDIMENT within the Trinity River Corridor. but consideration should be given to the probable risk of flooding. Sports fields can serve as detention basins by constructing berms around the facilities. Outflow can be 8.4.4 Other City Permits controlled through the use of an overflow weir or other

appropriate control structure. Proper grading must be 8 If a project includes moving more than 50 cubic yards of performed to ensure complete drainage of the facility. earthen material, then a grading permit is required. Recessed public common areas can also be utilized for FLOODPLAIN & SUMP DESIGN REQUIREMENTS stormwater detention but should be designed to flood infrequently. Maintenance considerations should be taken into account during design. 9 REQUIREMENTS OTHER REGULATORY OTHER REGULATORY

Figure 8.1 Critical Levee Zone C L 10 SUBMITTAL SUBMITTAL 100 N 50 L T 50 L T 100 N REQUIREMENTS G G L H

H 11 OPERATION & OPERATION E L T MAINTENANCE R R

Dallas Drainage Design Manual 113 APPENDICES 8.6 8.7 FEMA COORDINATION SUMP AND

Coordination with FEMA may be necessary if development LEVEE AREAS is proposed within an existing floodplain.

A Letter of Map Amendment (LOMA) shall be submitted Pre-development meetings with Director are required for to FEMA for a property that has been inadvertently any project in sump and levee areas. mapped in the floodplain but is on higher ground than the base flood elevation. 8.7.1 Sumps A Letter of Map Change (LOMC) shall be submitted to Sumps are drainage features of levee systems that FEMA if the floodplain area or designation is revised or temporarily store stormwater runoff before it is conveyed to amended based on the Flood Insurance Rate Map (FIRM). a river system by pumping over or draining through a levee. These areas must have a method of drainage to prevent A Letter of Map Revision (LOMR) shall be submitted standing water and allow for periodic maintenance. to FEMA if physical measures affect the hydrologic or hydraulic characteristics of a flooding source and thus result in the modification of the existing regulatory 8.7.2 Levee Setback floodway, the effective Base Flood Elevations (BFEs), or the Special Flood Hazard Area (SFHA). A LOMR officially The levees are designed as a safety measure to prevent revises the FIRM and and sometimes the Flood Insurance frequent flooding in areas near the floodplain. The levees Study (FIS). must be maintained and periodically inspected for structural integrity. A Letter of Map Revision based on Fill (LOMR-F) is FEMA’s modification of the SFHA shown on the FIRM Refer to USACE’s EM 1110-2-1913 for guidelines on based on the placement of fill outside the existing design and construction in and around levees and ETL regulatory floodway. 1110-2-583 for guidelines on landscape planting and vegetation management at levees. The Critical Levee Zone A Conditional Letter of Map Revision (CLOMR) can be is the area of highest concern and subject to the more submitted on a proposed project before construction but stringent requirements set forth by USACE for justifying will not be added to the FIRM until it is confirmed to have any proposed modifications. The Restricted Zone is been built as proposed. defined as the outer boundary of the 150-foot area from each levee toe for which reviews are required. Projects See FEMA’s online Flood Map Service Center for more within this defined zone may require 404 and/or 408 information about flood maps and submittals. The City’s permitting. Refer to Section 9.2 for further guidance. approval is required prior to any submittal to FEMA for FIRM map revisions.

114 Section 8 Floodplain & Sump Design Requirements 1 INTRODUCTION 2 HYDROLOGY 3 ROADWAY ROADWAY DRAINAGE DESIGN 4 BRIDGE HYDRAULIC DESIGN 5 DESIGN OPEN CHANNEL 6 DRAINAGE STORAGE DESIGN 7 CONTROL MEASURES EROSION & SEDIMENT 8 FLOODPLAIN & SUMP DESIGN REQUIREMENTS 9 REQUIREMENTS OTHER REGULATORY OTHER REGULATORY 10 SUBMITTAL SUBMITTAL REQUIREMENTS 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 115 APPENDICES

SECTION 9 Other Regulatory Requirements

Dallas Drainage Design Manual 117 9.1 9.2 GENERAL ENVIRONMENTAL

The design engineer is responsible for obtaining approvals AND CONSTRUCTION and maintaining compliance with any State or Federal regulations, permits, and programs including TCEQ, EPA, U.S. Army Corps of Engineers (USACE), FEMA or PERMITTING other agencies. The developer is required to provide the City with copies of all approved permits and associated REQUIREMENTS submittals required by any State or Federal agency for developments within City of Dallas. Refer to Article V Section 51A-5.100-5.105 for critical facility requirements. 9.2.1 Water Quality Refer to TPDES, which is under the provision of Section 402 of the Clean Water Act and Chapter 26 of the Texas Water Code and Chapter 19, Article IX, Section 19-118 of the Dallas City Code for water quality and pretreatment requirements.

These regulatory requirements set forth water quality standards for surface water, requiring permits for point discharges of pollutants into the Waters of United States. 9.2.2 Tree Mitigation Trees reduce stormwater runoff and are a natural filtration system. Care should be taken to protect the root system of a tree to maintain healthy trees and receive the full benefit of decreasing stormwater runoff and improving water quality.

New earthen facilities and alterations to existing facilities shall be planted with drought resistant, low growth, native species grasses which will allow unobstructed passage of floodwaters. Existing vegetation shall be preserved where possible. Even if existing above ground vegetation must be removed, remaining root systems may help stabilize soil while new vegetation is established.

Refer to Article X Sec. 51A-10.101 for landscape and tree preservation regulations. Natural vegetative buffers shall be maintained along riparian corridors if feasible in accordance with the TPDES Construction General Permit TXR150000.

A mitigation plan will be required if the above minimum preservation requirements are not met.

118 Section 9 Other Regulatory Requirements City ofDallas. requirements, ascoordinatedwiththeUSACE,through may alsobeusedtosupportSection404permit in coordinationwithCityStaff.TheBiologicalAssessment implemented bytheTexas DepartmentofParks&Wildlife Parks &WildlifeCode66.015.Thesepermitsare Plan byacertifiedbiologistinaccordancewith Texas require aBiologicAssessmentandAquaticRelocation or maintenanceactivitiesinnearpublicwatersmay Section 404/408permitrequirements,construction and tributariesthroughDallas.InadditiontoCWA of concernmaybeidentifiedinthe Trinity River Endangered freshwatermusselsandseveralspecies 9.2.5 AquaticRelocation floodway andtheDallasextension. is looselydefinedastheareaswithin1/4mileofDallas The areacomprisingthefederalprojectthroughDallas USACE website. of suchwork.”Permitapplicationscanbefoundonthe to thepublicinterestandwillnotimpairusefulness Army Corpsiftheuseormodification“willnotbeinjurious works project.PermissionisgrantedbytheSecretaryof regulates thealteration,occupation,oruseofUSACEcivil Section 408ofU.S.CodeTitle 33Chapter9SubchapterI, 9.2.4 Section408Permitting USACE website. the UnitedStates.Permitapplicationscanbefoundon or individualpermitisneededforfillwithinthe Waters of permits, USACEprovidesguidanceonwhenanationwide regional, orstatelevel.AstheadministratorofSection404 Many projectsfallunderageneralpermitatthenationwide, States, including,butnotlimitedtojurisdictionalwetlands. of dredgedfillmaterialsintothe Waters oftheUnited Section 404oftheCleanWater Actregulatesthedischarge 9.2.3 Section404Permitting information. available fromtheCity. ContacttheDirectorforadditional Trinity RiverFloodwayrequiresaAccessPermit All activityonthestreamsideofleveetoeswithin 9.2.6.3 FloodwayAccessPermits discussed inapredevelopmentmeeting. Questions regardingpermitrequirementsshouldbe project willberequiredtoobtaingradingandfillpermits. should beconsultedtodeterminewhetheraspecific for constructionactivities.TheCityofDallaswebsite City ofDallasgradingandfillpermitsareoftenrequired 9.2.6.2 CityGradingandFillPermits accordance withCityofDallasCodeSection19-118. Construction GeneralPermitasauthorizedbyTCEQandin the Texas PollutantDischargeEliminationSystem(TPDES) Construction activitymustbeperformedincompliancewith 9.2.6.1 TPDESConstructionGeneralPermits Requirements 9.2.6 ConstructionPermit Dallas DrainageDesign Manual 119

Table 9.1 Easement Widths

Total Structural Width (in) Easement Width (ft) 39” and under 15’ wide 42” – 54” 20’ wide 60” – 66” 25’ wide 72” – 102 30’ wide

120 Section 9 Other Regulatory Requirements for allaerialutilitystreamcrossings. crossings uponchannelconveyancemustbeconsidered upgrading andupsizing.Potentialimpactofutility and thepossibilityoffuturereplacement,including space neededforlongtermoperationandmaintenance configuration shallconsiderthoseutilitiesincludingthe in closeproximityorcrossoneanother, easement Where drainagefacilitiesandutilityinfrastructureare 9.3.6 anchors. structure willrequiresubsurfaceeasementsfortieback Some erosioncontrolprojectsforstreams<10feetfrom Attorney. for subsurfaceeasementistobediscussedwiththeCity etc.) requiresasubsurfaceeasement.Easementlanguage Infrastructure placedunderground(tiebacks,tunnels, 9.3.5 (Tunnels / Tieback Anchors) Utility Considerations Subsurface Easements Traffic/Safety, etc.). TxDOT Divisions(Legal,Right-of-way, Materials,Bridge, is compatiblewithothercriteriaanddesignfrom Irrigation Districts),andtoensurethedrainagedesign criteria (Cities,Counties,GeneralImprovementDistricts, Protection Agency(EPA), etc),appropriate localagency US ArmyCorpsofEngineers(USACE),Environmental Agency (FEMA),andregulatoryagencies(forexample Subparts AandB,FederalEmergencyManagement & Memos,CodeofFederalRegulationsTitle 23Part650 such asFederalHighwayAdministration(FHWA) Policy all relevantdrainagedesigncriteriaandrelatedpolicy, The designerisresponsibletoensuredesignscomplywith should beplannedaccordingly. for reviewandprocessing.Projectbudgetstimelines regulatory agenciesmayrequireadditionaltimeandcost agencies toreceiveCityapproval.Submittalsother Projects mustmeetrequirementsofotherregulatory OTHER AGENCIES COORDINATION WITH 9.4 website forCDCPermitrequirements. floodplain. RefertotheNCTCOG CommonVisionProgram which issimilartothe1%annual chance(100-year) area oftheTrinity floodplaincalled theRegulatoryZone, A CDCpermitisrequiredtodeveloplandwithinaspecific raise floodwaterlevelsorreducestoragecapacity. development thatdoesoccurinthefloodplainwillnot prohibit floodplaindevelopment,butensuresthatany along theTrinity River. TheCDCprocessdoesnot The NCTCOGCDCprocessaimstostabilizefloodrisk 9.4.2 NCTCOG permits fortheCountywhereinprojectislocated. The designershallcomplywithallapplicablecounty 9.4.1 CountyRequirements Dallas DrainageDesign Manual 121

Refer to USACE’s EC 1165-2-220 and SWFP 1150-2-1 for 9.4.5 USACE guidance when designing and constructing within federal project limits. Coordination with the USACE is necessary if proposed development is within the Trinity River floodway, or Refer to Sections 9.2.3 and 9.2.4 for guidance on 404 impacts the flow of “waters of the United States” as and 408 permitting. Refer to USACE’s SWFP 1150-2-1 defined by 40 CFR 230.3(s) as: for criteria on design and construction within the limits of existing federal projects and EC 1165-2-220 for policies 1. All waters which are currently used, or were used in and procedures for alterations to USACE projects. the past, or may be susceptible to use in interstate or foreign commerce, including all waters which are subject to the ebb and flow of the tide; 9.4.6 Texas Parks & Wildlife 2. All interstate waters including interstate wetlands; If construction or maintenance activity is taking place in or near public waters, an aquatic resource relocation 3. All other waters such as intrastate lakes, rivers, streams plan may be needed. Projects that are eligible include (including intermittent streams), mudflats, sandflats, pipelines, trenching, road/bridge construction, dam work, wetlands, sloughs, prairie potholes, wet meadows, dewatering, stream bank restoration, etc. Refer to Texas playa lakes, or natural ponds, the use, degradation or Parks & Wildlife Code 66.015 for regulation on aquatic destruction of which could affect interstate or foreign species within public waters. commerce including any such waters: Additionally, certain projects may require compliance with -- Which are or could be used by interstate or foreign Texas Parks & Wildlife Code Title S, Subtitle I, Chapter 90. travelers for recreational or other purposes; or -- (From which fish or shellfish are or could be taken 9.4.7 FEMA and sold in interstate or foreign commerce; or See Section 8.6 for coordination with FEMA for activities -- Which are used or could be used for industrial within a FEMA-designated floodplain. purposes by industries in interstate commerce;

4. All impoundments of waters otherwise defined as 9.4.8 DART and Other Rail Systems waters of the United States under this definition; Any project that includes construction within the right-of- 5. Tributaries of waters identified in paragraphs (1) way of DART (Dallas Area Rapid Transit) or any other rail through (4) of 40 CFR 230.3(s); system must include coordination with the appropriate angency and must obtain all applicable permits necessary 6. The territorial sea; for project design and construction activities.

122 Section 9 Other Regulatory Requirements criteria shallbeusedfortheproject. required betweenallinvolvedentities.Themorestringent If theprojectislocatedinmultiplecities,coordination 9.4.9 NeighboringCities Dallas DrainageDesign Manual 123

SECTION 10 Submittal Requirements

Dallas Drainage Design Manual 125 10.1 10.2 GENERAL PLATTING /

This section outlines the steps involved in preparing DEDICATION OF submittals and construction plans for the City. Some variation for private development plans is expected; specific guidance should be obtained from the City WATER COURSES of Dallas Sustainable Development and Construction Department. Refer to the Street Design Manual for AND BASINS additional requirements for storm drainage plans submitted with paving plans and for drafting standards. Property developments containing Floodway Management Areas, Floodway Easements, Detention Easements, or Drainage Easements shall have on the plat standard language addressing the easements and management areas, and on-ground monumentation.

Fill or development is prohibited in designated or undesignated 1% annual chance floodplain areas except as allowed under the floodplain fill or floodplain alteration permit process (Article V of the Dallas Development Code, Division 51A-5.100-5.105).

126 Section 10 Submittal Requirements - - - - shall includethefollowingelementsasappropriate: information mayberequired.Thedrainagereportnarrative to theproject.Site-specificdocumentsandadditional The followingguidelinesshallbefollowedasapplicable for submittalrequirementsfloodplainpermits. Section 51A-5.100-5.105oftheDallasDevelopmentCode that canadverselyimpactwaterquality. RefertoArticle V increase instormwaterrunoffandtotreatthepollutants determine theimprovementsnecessarytocontrol impacts resultingfromlanddevelopmentactivitiesand The purposeoftheDrainageReportistoidentifydrainage flash drive,orotherelectronicmediaasapprovedbytheCity. the CityandaPDFofreportmustbeincludedonCD, A hardcopyofthedrainagereportshouldbesubmittedto 10.3.1 DrainageReports electronic mediaasapprovedbytheCity. files mustbeincludedonaCD,flashdrive,orother Hydraulic modelsandrelevantGIS,CAD,orMicrostation additional requirementsforstormdrainageplanssubmittal. must besubmitted.RefertotheStreetDesignManualfor Hardcopy andelectronicsetsofsupportingdocumentation All supportingdocumentationmustbesubmitted. REQUIREMENTS DOCUMENTATION 10.3 - - - - areas ofeach sub-basin). water surfaceelevations,impervious andpervious driveways, curvenumbers/runoff coefficients,flows, Post-development basininformation (Sizeofroofs& other specialfeaturesnearproject). systems, flows,watersurface elevations,andany drainage facilities,naturalorconstructed,conveyance Pre-development basininformation(On-site&Off-site and soiltypeexhibits. Topographic conditions,precipitationdata,landuse background informationrelevanttodrainagedesign). Project description(sizeoftheproject,location, ------calculations include,butarenotlimitedto: used todeterminethesizeoffacilities.Typical The DrainageReportshallincorporateallcalculations Applicable FEMAfloodplainmaps Existing andproposeddrainageareamaps. shall beincluded. connections toexistingorproposedregionalfacilities A discussionofanyexpectedfutureimpactsonor the finalDrainageSubmittal. be obtainedandrecordedpriortotheacceptanceof outside theprojectboundaries.Theseeasementsshall proposed stormwaterconveyanceordisposalfacilities schematic. Off-siteeasementswillberequiredfor be identifiedeitheronthebasinmaporinaseparate The anticipatedlocationofanyoff-siteeasementsshall operation ofthestormwatersystem. Sufficient informationshallbeprovidedaboutthe rates andvolumesshallalsobeincluded. developed conditionsatprojectoutfallsincluding A tablecomparingthepre-developedandpost- the proposedstormwaterfacilitiesshallbeincluded. The resultsofthecalculationsandadescription Discussion offuturedevelopment. Discussion ofdownstreamcapacity. proposed fortheproject. sizing thedrainagefacilities,includingBMPs The hydraulicmethodsandstormeventsusedin gradient oftheprojectsite. Identify anddiscusstheprobableimpactsdown------Flow spreadcalculations Energy dissipationcalculations Culvert andpipecalculations Calculations forditchesand naturalchannels overflow calculations Inlet capacity, bypass,andsecondary Water qualitytreatmentcalculations Curve number(CN)orrunoffcoefficient(C) Time of concentrationcalculations table orpondvolumecalculations structures, orificeinformation,apondvolumerating routing calculations,designinformationforoutflow post-developed peakrateandvolumecalculations, Hydrologic/hydraulic calculationsincludingpre-and Dallas DrainageDesign Manual 127

All plan sets must include a Horizontal and Vertical Control Figure 10.2 Outfall Ditch Survey Example Less Than 3ft drawing, produced in accordance with City of Dallas Standards, signed and sealed by a Texas Registered Professional Land Surveyor, and submitted to the Survey Division for review. The names of all owners, if raw land, T S T S and all subdivisions abutting the project must be shown. The datum for all coordinate shown must be given. The basis of bearings must be stated on the drawing.

Rivers, stream, creeks, and outfall ditches will all be surveyed in varying distances as per project scope and B engineering requirements. Projects require pre-project and as-built survey based on at least two City of Dallas B survey control network monuments. All elevations shall be referenced to the latest vertical datum.

Drainage features are commonly surveyed a reasonable distance upstream and downstream from the end of the drainage structure as necessary to adequately define T S project tailwater and headwater conditions. The following are some general guidelines for locating and collecting cross section survey data. B

L B T S

T S

B 128 Section 10 Submittal Requirements L

B L B 4. 3. 2. 1. 10.3.2.2 OutfallDitchesMoreThan3ftWide Figure 10.5FloodplainLocationMethods S M SS 1. Includeallgrade breaks Ground PointSpacing Vertical spacing-20%ofR V =Spacedtosatisfyverticallimit Inmainchannel -10%ofC G =Significantgradebreak Infloodplain-5%ofW 2. Intermediategroundpointspacing: 1. Includeallgradebreaks Ground PointSpacing: 2. Intermediate spacing=10%ofW define theshape/conveyancecapacityofditch Provide additionalpointsasnecessarytoadequately bottom ofthefeature Provide two(2)DrainLines(ODL)alongthetoeor the feature Provide aminimumoftwo(2)breaklinesalong Ditch (DL)alongthetopoutsideedgeoffeature Provide two(2)Top ofBank(TS),Creek(CR),or STA 0+00(lookingDS) STA 0+00(lookingDS) W 10 max 20 W (Cross SectionWidth) (Cross SectionWidth) W V Figure 10.4OutfallDitchSurveyExampleMoreThan3ft Figure 10.3OutfallDitchSurveyMoreThan3ft B B T S T S L W FT min B T S G G B L (Main ChannelWidth) G L C R =Range Right BankTerminal V B G G C V 10 B max Right BankTerminal Dallas DrainageDesign Manual Define DrainLine Define Top ofBank T S B T S B 129

-- Culvert locations need to include the culvert -- Special field conditions (crushed end, fully silted, etc) inside dimensions 10.3.2.5 Minor Headwalls and Wingwalls --BMulti-Barrel culverts are located by barrel Locate Minor Structure wingwalls and headwalls in the -- Wingwall & Headwall locations need to include wall width B same fashion as major structures. Walls are generally not Figure 10.6 Culvert Survey Detail included in the DTM file, so be sure to collect sufficient elevation data around the structures. Wing Wall Located at Face of Wall Figure 10.8 Minor Drainage Wingwall T S Top of Embankment Culvert Elevation Apron LocationB Shots Shots Location (DTM)

Wall Located at Locate Top Locate Top Face of Wall Front of Front of Wing L DTMB Shots T S Headwall Walls Behind Wall

Figure 10.7 Culvert Survey Example

T S Locate Pipe Invert B

B L B

130 Section 10 Submittal Requirements Back ofSidewalk mapping floodplains. Manual fortherequiredstandardssurveyingand Refer totheFHWA ProjectDevelopmentandDesign required forallstreamandfloodplaincross-sections. Flood HazardMappingProgram.Similarlevelofdetailis Figure 10.5depictsthemethodologyusedbyFEMAfortheir - - - Some majoraspectsofthesestandardsareasfollows: 10.3.2.7 FloodplainSurveys Figure 10.9CatchBasinLocations - - - - of shotsdepictingthefollowinginformation: Curb Inletsaregenerallylocatedwithaminimalamount 10.3.2.6 InletStructures ------comprehensive depictionofthefloodplain Aerial surveysareoftenthebestwaytoprovidea topography oftheplain Cross-sections shouldindicatethegeneralslope& supplemented byaerialtopography floodplain orincludethefullwidthofchannel Cross-section datamustincludefullwidthofthe Edge ofpavementlocation/elevation Face ofcurblocationandtopelevation Curb FlowLineElevationShot description oftypeorsize Center Top ofStructurewithstructurecodeand Code &Description Locate CenterofStructure Face ofCurb Locate FlowLineShot Edge ofPavement the CityofDallasstandardsandspecifications. design. Ataminimum,theplansshallmeetcriteriaof to constructtheproposedfacilitiesperengineer’s drainage plansshallprovideenoughdetailforathirdparty construction plansfortheCityofDallas.Theroadand This sectioncoversthepreparationofdrainage 10.4.1 General PREPARATION CONSTRUCTION PLAN 10.4 can beeliminatedfromfurtherconsideration. estimate maybenecessarytodetermineifanyoptions and affectedagencies.Anorderofmagnitudecost alternatives shouldbediscussedwiththeprojectteam obvious undesirabledrainageimpacts.Feasibledesign an orderofmagnitudeevaluationtoidentifyflawsor a leveltodetermineifoptionsarefeasible,i.e.,thisis etc. Drainageanalysisanddesignisonlydevelopedto (FEMA) floodzones,environmentallysensitiveareas, impacts suchasFederalEmergencyManagementAgency preferred alternativesbasedondrainageimpacts,i.e., from consideration.Thelevelofeffortshouldalsoidentify that resultinlessdesirablealternativesbeingdropped most viabledesignalternativesandtoidentifyanyflaws The conceptualdesignphaseisusedtodevelopthe warrant additionalconsideration. phase istodeterminethemostviablealternativesthat alternatives. Themainpurposeoftheconceptualdesign interchange types,etc.,eachwithconceptualdrainage There maybeseveralviableroadwayalignmentcorridors, In thisphase,majorprojectelementsareconsidered. 10.4.2 ConceptualDesignPhase Dallas DrainageDesign Manual 131

1. Area map showing the section or part of the section in A design checklist is located on the City of Dallas website. which the site is situated 2. Location and description of all activities that may 10.4.4 Pre-Final Design Phase impact, or be impacted by, the proposed development or redevelopment both on and off the site During this phase, all design decisions are completed. The major goal of this phase is to develop the design 3. Acreage of the total site and acreage of the area being to a level adequate to determine all right-of-way needs. affected by the development This submittal is intended to be 100% complete and will be used for the checking and specifications review. 4. A conceptual layout of the proposed drainage system All drainage QA/QC review is to be completed prior to for the development or redevelopment this submittal. The Special provisions and plans will be distributed to provide a complete package for the entire 10.4.3 Preliminary Design Phase review team. The preliminary design phase consists of the development A design checklist is located on the City of Dallas website. of the project in sufficient detail to allow review for compliance with design criteria. Preliminary submittal 10.4.5 Final Design Phase for City projects shall conform to requirements given in the engineering services contract. Topographic surveys The final design phase consists of preparing construction developed by approved methods should be furnished to plans in final form. All sheets shall be drawn on a 22 inch allow establishment of alignment, grades and right-of-way x 34 inch mylar sheet. Refer to City of Dallas Survey Vault requirements for all City projects. Any methods other than for mylar requirements. The drawings shall be executed in field survey shall be field verified. Field notes shall be such a manner that they shall be legible when reduced to furnished for all City of Dallas projects. half size. For all computerized drawings, a level list shall be submitted. For Private Development where offsite easements are proposed, field notes shall be signed and sealed by a Review comments shall be addressed, additional data Registered Professional Land Surveyor and shall begin incorporated, and final design and drafting completed. at an established point such as a street intersection or Grades, elevations, pipe sizes, utility locations and a corner of an established subdivision. The notes shall elevations, items and quantities should be checked. be accompanied by a deed of ownership and a location Each plan profile sheet should reference two permanent map. All easements pertaining to Private Development bench marks shown on the plan in their correct location should be submitted to the Sustainable Development and and annotated on the lower right corner of the plan view. Construction Department. Permanent bench marks shall be located outside the limits of construction. Structural detail sheets, quantity The hydrologic and hydraulic design is to be based on sheets, and horizontal control sheets (if required by the the criteria outlined in Section 2 and 3 of this manual. All engineer) shall be completed and submitted. calculations shall be submitted with the preliminary plans. These plans shall show the alignment, drainage areas, Structural analysis computations should be provided in size of facilities and grades. a legible form for any proposed structure not included in the City of Dallas 251D-1 Standard Construction Details. The designer shall be responsible for determining the Items on the plans requiring special provisions and special elevation and location of a utility which may be close to construction techniques should be clearly delineated on a proposed storm drain line and for showing the utility the plans and should be specifically called to the City’s accurately on the plans with station, elevation and source attention by letter prior to final plan submission. of elevation given in the profile. Utilities suspected to be within 5 feet of proposed facilities shall be field located A design checklist is located on the City of Dallas website. by probing or exposure. Each utility company shall be The design checklist shall be filled out and provided with contacted with regard to its policies and procedures for the submittal. uncovering its respective utility.

132 Section 10 Submittal Requirements 7. 6. 5. 4. 3. 2. 1. drainage areamap: The followingitems/informationshallbeincludedinthe watersheds unlessapprovedbytheDirector. There shallbenodiversionofdrainagebetween inlet calculationsshallbeapartofthedrainageareamap. be shownanddelineated.Runoffcalculationsincluding All off-sitedrainagewithinthenaturalbasinshall improvement sheetlimitsshallalsobeshown. drainage areamap.Plan-profilestormseweror channels shallbeclearlyshownanddifferentiatedonthe drainage inlets,stormsewerpipesystemsand shown onthedrainageareamap.Existingandproposed drainage ways,andallsystemintersectionsshallbeclearly Direction offlowwithinstreets,alleys,natural&man-made define hydrologicresponsewithinthewatershed. necessary toprovidedesigninformationandadequately determine flowconcentrationpointsorinletlocationsas 5 feet.Theareashallbefurtherdividedintosubareasto determined fromamaphavingcontourintervalof1to into theproposedsystem.Thisboundarycanusuallybe show theboundaryofdrainageareacontributingrunoff area. Whencalculatingrunoff,thedrainageareamapshall right-of-way) issuitableunlessdealingwithalargedrainage a maphavingscaleof1"=200'(showingthestreet provide therequiredinformationandtobelegible.Generally, in Section2.Themapshallbedrawnatascalenecessaryto the methodtobeusedincalculatingrunoffasdiscussed The scaleofthedrainageareamapshouldbedeterminedby 10.4.7.1 DrainageAreaMap 10.4.7 PlanRequirements Refer totheStreetDesignManualfordraftingstandards. 10.4.6 DraftingRequirements adjacent additions and/orlots Runoff toallinlets,dead-end streets,andalleysorto Zoning boundariesandzoning foreacharea Subareas foralleys,streets, and off-siteareas Existing andproposedstormsewers centerline station the directionofflowindicatedbyarrows, Inlets, theirsizeandlocation,theflow-byforeach, drainage sub-area Acres, runoffcoefficientandrainfallintensityforeach first reviewandincludedonthemapwithfinal Chart includingdatashownshallbesubmittedwiththe 15. 14. 13. 12. 11. 10. 9. 8. 6. 5. 4. 3. 2. 1. show thefollowing: The planportionofthestormdrainplan/profilesheetshall 10.4.7.2 Plan/ProfileSheets - - - - - on 5’orsmallerincrementcontours define drainagebasinboundariesandshallbeshown Contour intervalsshallbeasnecessarytoadequately Drainage dividesshallbefieldverified shall beindicatedontheDrainageAreaMap Pre &PostProject1%annualchanceFloodplain facilities shallbeincluded line indicationofthelocationpipesandother (Forms areprovidedinAppendixA.5),andasingle 515D (Bridges)numbersshallbeshownonthemap Profiles),428Q (StormSewerFloodwaySystem),and All pertinentfiles;421Q(StormSewerPlats& Streets andstreetnamesshallbeindicated Any off-sitedrainageshallbeincluded alley intersections Flow arrowstoindicateallcrests,sags,andstreet input dataandpeakdischarges A tableforrunoffcomputationsorunithydrograph The conduitshallbeshadedforemphasis. in sizeclearlyindicatedastheyoccur. centerline andtwosidesoftheconduitwithchanges The planofthestormdrainshallbedrawnwitha the stormdrain. pipe, anditemnumbershallbeshownadjacentto In theplanview, thestormdraindesignation,sizeof advance bytheCityEngineer. system. Anyvariationinscalemustbeapproved may requiredifferentscalestoadequatelyshowthe of 1inchequals6feet.Unusuallylargeconduits scale of1inchequals20feetandavertical Plan /profilesheetsshallbepreparedonahorizontal and eachsheetshallbeginendwithevenstationing. The drainplanshallbestationedat100-footintervals, the followingcurvedatashallbeshownonplan: If thestormdrainalignmentrequiresahorizontalcurve, - - - - - Length ofCurve Tangent Distance Radius Deflection Angle PI Station Dallas DrainageDesign Manual 133

9. Manholes shall be provided and shown on the plan / 2. Design discharge (cfs) profile sheet. 3. Slope of hydraulic gradient (ft/ft) 10. Existing topography, storm drains, sprinkler heads, double check assemblies, inlets, curbs, driveways, 4. Capacity of pipe (cfs) (Assuming the hydraulic pavement, manholes, meters, valve boxes, trees, gradient equals the pipe grade) shrubs, and fences, etc., within the right-of-way, shall 5. Velocity (ft/s) be shown on the plan with existing pavement type and thickness noted. 6. Velocity head (V 2/2g) (ft)

11. Item numbers shall be shown for all items of work to 7. Limits and velocity of partial flow where applicable be accomplished. Inlets shall be given the same number designation as the 12. A summary of quantities sheet is to be provided. area or sub-area contribution runoff to the inlet. The inlet number designation shall be shown opposite the inlet 13. Two permanent bench marks shall be referenced in the lower right corner of each plan view sheet. All Data opposite each inlet shall include paving or storm bench marks shall be checked out by a level circuit sewer stationing at centerline of inlet, size of inlet, type submitted to the City. of inlet, number or designation, top of curb elevation and flow line of inlet as shown on the typical plans. Lateral 14. The storm drain profile is to be positioned on the sheet profiles shall be drawn showing appropriate information so that the stationing in the plan is approximately including the hydraulic gradient. adjacent to the stationing in the profile. Even 100-foot stations shall be shown at the bottom of the profile, The hydraulic grade adjustment at each interception point and elevations at 5-foot intervals shall be shown at the should be shown. Partial flow should be shown by labeling left and right sides of the profile sheet. starting and ending stations clearly.

15. Stationing for drainage and paving profiles must be Elevations of the flow line of the proposed storm drain oriented in the same direction. are to be shown at 50-foot intervals on the profile. Stationing and flow line elevations are shown at all pipe 16. Laterals shall be shown in the profile when they cross grade changes, pipe size changes, lateral connections, an existing utility, when they drain a sag or when they manholes and wye connections. Pipe wyes connecting exceed 12 feet in length. to the storm drain shall be made centerline to centerline, The profile portion of the storm drain plan / profile sheet shown in the profile with the size of lateral, flow line of wye shall show the following: and stationing of storm sewer indicated.

1. Elevations of rock line (at boring locations) Boring locations with elevations of top of rock should be included on the drainage plans, as well as all existing and 2. Soffit proposed drainage easements, rights-of-way, letters of permission and required temporary easements. 3. Invert In preparing the final plans, the Engineer shall ensure that 4. Hydraulic grade line inlet elevations and stations are correctly shown on the storm drainage, structural and paving plans as applicable. 5. Top of pipe Inlet locations on storm drain plans shall conform to inlet 6. Existing ground and proposed finished grade at locations as shown on the drainage area map. Proposed centerline of pipe pavement location shall be cross-referenced and agree horizontally and vertically with paving plans, storm drain 7. Elevation of intersecting utilities plans, structural plans and cross-sections, and existing topographic features. 8. Diameter of the proposed pipe

9. Pipe grade in percent

134 Section 10 Submittal Requirements plans shallbeprovidedwhenrequiredbytheDirector. temporary), andwarningsigns.Detourtrafficcontrol and handrailings,specialbarricades(permanent and specialinletsshouldbeprovidedaswellbridge walls, headwalls,junctionboxes,culverts,channellining, Details. Structuraldetailsforbridges,specialretaining File 251D-1aretobeincludedintheplansasSpecial Details notshownintheStandardConstructionDetails, 10.4.7.3 SpecialDetails Dallas DrainageDesign Manual 135

SECTION 11 Operation and Maintenance

Dallas Drainage Design Manual 137 11.1 11.2 OPERATION AND OPERATION AND MAINTENANCE MAINTENANCE PLANS

CONSIDERATIONS An operation and maintenance plan (O&M Plan) shall be provided for all pump stations and detention facilities that Drainage features should be maintained to ensure that will not be City owned and operated. At a minimum, the capacity and water quality objectives are being met. Regular O&M Plan should include: operation and maintenance activities extend the optimal -- The name and contact information of the party (or function of stormwater infrastructure and landscape design parties) responsible for maintenance and operation and treatments. Significant repair and restoration costs can of the system, such as a Home Owners association, be avoided with regularly scheduled maintenance. management company or the legal property owner.

Closed-circuit television (CCTV) inspection is required for -- Property legal description, address, and project newly installed or rehabbed conduits. name, if applicable.

Maintenance access should be provided for all drainage -- Agreement to maintain facilities in accordance with elements in accordance with the size of equipment necessary City of Dallas minimum maintenance standards, to maintain. Access routes, including roadways and provided in the Appendix A.6. sidewalks, shall be inspected annually and maintained as needed. -- The O&M Plan and a log of maintenance activities that indicates what actions have been taken, when Corrective measures should be taken if flowpaths appear and by whom shall be made available for inspection that short-circuit the drainage system. by City of Dallas upon request.

See Appendix A.6 for an Operation & Maintenance Plan -- Maintenance instructions for any components not Template. Maintenance responsibility should be noted on covered by the minimum maintenance standards in the plat. Appendix A.6.

-- Maintenance manual of any proprietary device specified

-- The engineer’s narrative description of the storm drainage system and how it is intended to function.

-- Site diagram of the constructed (as-built) storm drainage system, identifying its components, with profiles as needed.

-- As-built details of components.

A copy of the O&M Plan shall be retained onsite or within reasonable access to the site, and shall be transferred with the property to the new owner. The O&M Plan shall be adjusted or revised at the end of the first year of use, if needed, as a result of inspection findings and recommendations by the City. O&M plans shall be

138 Section 11 Operation & Maintenance testing proceduresshallbeincludedintheO&MPlan. within floodplainareas.Ifinfiltrationtestingisrequired, Section 51A-5.208forvegetationplanrequirements applicable projects.RefertoDevelopmentCodeArticle V, Vegetation managementplans arerequiredforall are operatingasintended. performed byaqualifiedengineertoensurethatfacilities to theapprovedO&MPlan.Annualinspectionsshallbe and operation.Futurelandownersarerequiredtoadhere document mustbefiledwiththeCityformaintenance If aneasementalreadyexists,aseparateinstrument filed withtheCourthouseplatordeedrecords. Dallas DrainageDesign Manual 139

Appendices

Dallas Drainage Design Manual 141 A.1.1 Applicable Regulations City of Dallas Procedures for Filling in a Flood Plain Under the Flood Plain Management Guidelines

City of Dallas Plat Regulations A.1 Code of Federal Regulations Title 23 Part 650 Subparts A & B Dallas Development Code Article V Ch. 51 GENERAL Dallas Development Code Article V Ch. 51A Dallas Development Code Article X Ch. 51A

Dallas Municipal Separate Storm Sewer System (MS4) Permit

Escarpment Ordinance

North Texas Council of Governments Corridor Development Certificate

Section 408 U.S. Code Title 33 Chapter 9 Subchapter I

Standard Details (251-D)

Texas Administrative Code Title 30, Part 1, Chapter 210 Subchapter F

Texas Administrative Code Title 30, Part 1, Chapter 299

Texas Parks & Wildlife Code 66.015

Texas Parks & Wildlife Code 90.008

Texas Pollutant Discharge Elimination System General Permit Relating to Stormwater Discharges Associated with Construction Activities

Texas Pollutant Discharge Elimination System General Permit TX040000 (MS4 Permit)

Texas Water Code Title 2 Subtitle B Chapter 11 Subchapter A

Texas Water Code §11.142

USACE EC-1162-2-220

USACE EM 1110-2-1913

USACE ETL 1110-2-583

USACE SWFP 1150-2-1

40 CFR Part 122

44 CFR Part 65

142 Appendices 1 INTRODUCTION A.1.2 List of Acronyms and PICP – Permeable Interlocking Concrete Pavement PFDS – Precipitation Frequency Data Server

Abbreviations 2

SCS – Soil Conservation Service HYDROLOGY ADA – Americans with Disabilities Act SFHA – Special Flood Hazard Area AEP – Annual Exceedance Probability SWPPP – Stormwater Pollution Prevention Plan

ASTM – American Society for Testing and Materials 3

TCEQ – Texas Commission on Environmental Quality ROADWAY

BMP – Best Management Practice DRAINAGE DESIGN TPDES – Texas Pollutant Discharge Elimination System CCTV – Closed-Circuit Television TXDOT – Texas Department of Transportation

CDC – Corridor Development Certificate 4

USACE – United States Army Corps of Engineers BRIDGE CLOMR – Conditional Letter of Map Revision HYDRAULIC DESIGN USGS – United States Geological Survey CN – Curve number

CRS – Community Rating System A.1.3 Glossary of Terms and 5 DESIGN DART – Dallas Area Rapid Transit Definitions OPEN CHANNEL DWU – Dallas Water Utilities Annual Exceedance Probability / Annual Chance Storm Event – defined as a percentage based on the probability EPA – Environmental Protection Agency that a certain amount of rainfall will be exceeded any 6 DRAINAGE

FEMA – Federal Emergency Management Agency given year. STORAGE DESIGN

FHWA – Federal Highway Administration Backwater – the increase in the upstream water surface level resulting from an obstruction to flow, such as a FIRM – Flood Insurance Rate Map roadway fill with a bridge or culvert opening placed on floodplain; can also describe the increase in water surface 7 GIS – Geographic Information Systems elevations near the confluence of one stream with another, CONTROL MEASURES caused by flood conditions on the larger stream. EROSION & SEDIMENT HEC-HMS – Hydrologic Engineering Center’s Hydrologic Modeling System Best Management Practices – a practice, or combination of practices, that is determined to be an effective and HEC-RAS – Hydrologic Engineering Center’s River practicable (including technological, economic, and Analysis System institutional considerations) means of preventing or 8 LEED – Leadership in Energy and Environmental Design reducing the amount of pollution generated by non-point FLOODPLAIN & SUMP

sources to a level compatible with water quality goals. DESIGN REQUIREMENTS LOMA – Letter of Map Amendment C Value – the runoff coefficient; a dimensionless LOMC – Letter of Map Change coefficient relating the amount of runoff to the amount of precipitation received. It is a larger value for areas with

LOMR – Letter of Map Revision low infiltration and high runoff (pavement, steep gradient), 9 and lower for permeable, well vegetated areas (forest, flat REQUIREMENTS

LOMR-F – Letter of Map Revision based on Fill land). OTHER REGULATORY

MS4 – Municipal Separate Storm Sewer System Coincident Peak – occurs when both streams reach their NCTCOG – North Central Texas Council of Governments peak flow, for a given return period, at the confluence of the streams at or near the same time, affecting the water 10 SUBMITTAL SUBMITTAL

NEH – National Engineering Handbook surface elevation of each stream. REQUIREMENTS

NOAA – National Oceanic and Atmospheric Administration Coincidental Occurrences – refers to the varying amount of time it takes for different size drainage basins to reach NRCS – Natural Resources Conservation Service peak flow; allows for storm drains to be designed to 11 different design storm frequencies based on area ratios of OPERATION & OPERATION MAINTENANCE NWS – National Weather Service receiving stream area.

Dallas Drainage Design Manual 143 APPENDICES Curve Number – an expression of the imperviousness of Hydraulics – the mechanical properties of water and other the land under fully developed conditions and the runoff liquids and the application of these properties in engineering potential of the underlying soil. Hydrograph – a plot of the variation of discharge with Easement – the grant of a nonpossessory property interest respect to time (it can also be the variation of stage or that grants the easement holder permission to use other water property with respect to time). another person’s land. Hydrology – the study of water, generally focusing on the Escarpment Face – the portion of the escarpment zone distribution of water and interaction with the land surface between the crest and the toe. and underlying soils and rocks.

Escarpment Line – the line formed by the intersection Infiltration – the process by which precipitation or water of the plane of the stratigraphic contact between the soaks into subsurface soils. Austin chalk and the Eagle Ford shale formations and the surface of the land. In-situ – Latin phrase meaning “on site” or “in position”.

Escarpment Zone – the corridor of real property south of Lag Time – the time from the center of mass of excess Interstate Highway 30 between the following described rainfall to the hydrograph peak; when using the SCS Unit vertical planes: Hydrograph method, lag time can be defined as 60% of the time of concentration for the basin. A) On the crest side of the escarpment line and measuring horizontally from that line, the vertical Lateral – the pipe that connects individual homes, plane that is 125 feet from that line, or 35 feet businesses, etc. to the main storm drain line. beyond the crest, whichever is farther from that Off-line System – systems that only treat runoff up to line. the design storm event that require a separate bypass B) On the toe side of the escarpment line and structure for storm events greater than the design storm measuring horizontally from that line, the vertical that can be routed around the system. plane that is 85 feet from that line, or 10 feet On-line System – systems that allow storm events that are beyond the toe, whichever is farther from that line. greater than the design storm to be bypassed through the Floodplain – any land area susceptible to inundation by treatment unit, eliminating the need for a separate bypass the design flood. structure.

Floodway – the channel of a river or other watercourse Permeability – the ability of soil or material to transmit and the adjacent land areas that must be reserved in water or air; when used in sustainable drainage measures, order to discharge the design flood without cumulatively permeable describes a system that allows movement of increasing the water surface elevation or to discharge water and air around the paving material. Water enters more than a designated height or rate. the joints between the solid impervious pavers and flows through the paver system. Forebay – a human-made pool of water in front of a larger body of water; can serve a variety of functions including a Porosity – the percentage of pore volume or void space, or buffer zone during storms, trapping sediment and debris, that volume within rock that can contain fluids. and acting as a natural habitat for aquatic life Porous – admitting the passage of gas or liquid through Freeboard – a factor of safety expressed in feet above a pores; when used in sustainable drainage measures, porous design water surface describes pavers that are a cellular grid system filled with dirt, sand, or gravel through which water can infiltrate. Froude Number – a dimensionless value that describes different flow regimes of open channel flow Probable Maximum Precipitation – theoretically, the greatest depth of precipitation for a given duration that is physically Headwater – the depth of water at the upstream end of possible over a given size storm area at a particular a culvert or drainage structure, as measured from the geographic location during a certain time of year. upstream invert of the culvert or drainage structure to the water surface elevation

Hydraulic Grade Line – the locus of elevations to which the water would rise if open to atmospheric pressure (e.g. piezometer tubes) along a pipe run.

144 Appendices 1

Probable Maximum Flood – the flood that may be Sustainable Drainage Measures – stormwater INTRODUCTION expected from the most severe combination of critical infrastructure that uses vegetation, soils, and other meteorologic and hydrologic conditions that are elements and practices to restore some of the natural reasonably possible in the drainage basin under study. processes required to manage water and create healthier 2 urban environments; sustainable drainage measures HYDROLOGY Riprap – rock or other material used to armor shorelines, include a range of soil-water-plant systems that intercept streambeds, bridge abutments, pilings, and other shoreline stormwater, infiltrate a portion of it into the ground, structures against scour and water or ice erosion. evaporate a portion of it into the air, and release a portion of it slowly back into the sewer system. 3

Roughness coefficient – designated by “n” in Manning’s ROADWAY flow equation, the roughness coefficient is an expression Stormwater – water that originates during precipitation DRAINAGE DESIGN of the resistance to flow of a surface such as the bed or events and snow/ice melt. Stormwater can soak into the bank of a stream. soil, be held on the surface and evaporate, or runoff and end up in nearby streams, lakes, and rivers. Runoff – surface runoff is the flow of water that occurs 4 BRIDGE when excess stormwater, meltwater, or other sources State water – as defined in Texas Water Code Title 2 flows over the Earth’s surface. Subtitle B Chapter 11 Subchapter A: HYDRAULIC DESIGN

Sedimentation – the natural process in which material A) The water of the ordinary flow, underflow, and (such as stones and sand) is carried to the bottom of a tides of every flowing river, natural stream, and 5 body of water and forms a solid layer. lake, and of every bay or arm of the Gulf of DESIGN Mexico, and the storm water, floodwater, and OPEN CHANNEL Shear Stress – a measure of the force of friction from rainwater of every river, natural stream, canyon, a fluid acting on a body in the path of that fluid. In the ravine, depression, and watershed in the state is case of open channel flow, it is the force of moving water

the property of the state. 6 against the bed of the channel. DRAINAGE

B) Water imported from any source outside the STORAGE DESIGN Short-circuiting – when a system is designed with flow boundaries of the state for use in the state and path geometry that allows bypass of the treatment system. which is transported through the beds and banks of Examples of short-circuiting in a bioretention area include any navigable stream within the state or by utilizing inlets or curb cuts that are very close to outlet structures any facilities owned or operated by the state is the or incoming flow that is diverted immediately to the 7 property of the state. underdrain through stone layers. CONTROL MEASURES Tailwater – the depth of water at the downstream end of EROSION & SEDIMENT Standard Project Flood – the flood expected from the most a culvert or drainage structure, as measured from the severe meteorological and hydrologic conditions that are downstream invert of the culvert or drainage structure to reasonably characteristic to the project area. A standard the water surface elevation. project flood usually has between 0.3 and 0.08 percent probability of being equaled or exceeded any given year. Time of Concentration – the time required for runoff 8 to travel from the furthest point, hydraulically, within

Subcritical Flow – deep slow flow with a low energy state FLOODPLAIN & SUMP

the delineated area (or watershed) to the outlet of the DESIGN REQUIREMENTS and has a Froude number less than one; the flow at which drainage area (or watershed). the depth of the channel is greater than critical depth, the velocity of flow is less than critical velocity, and the slope Unit Hydrograph – a hydrograph having a volume of 1 of the channel is also less than the critical slope. inch of runoff which is associated with a precipitation event of specified duration and areal pattern (uniform over 9 Sumps – drainage features of levee systems that temporarily

the basin); a theoretical hydrograph which is intended to REQUIREMENTS

store storm water runoff before it is conveyed to a river system OTHER REGULATORY describe how a river at a particular point will react to 1 by pumping over or draining through a levee. inch of runoff, and can in turn be used to derive how the Supercritical Flow – shallow fast flow with a high energy river will react to any amount of runoff. state and has a Froude number greater than one; the 10 Valley Storage – the water volume between the water flow at which the depth of the channel is less than critical SUBMITTAL surface and ground surface that occupies a given reach REQUIREMENTS depth, the velocity of flow is greater than critical velocity of the river. and the slope of the channel is also greater than the critical slope. 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 145 APPENDICES A.1.4 Sources

Table 2.4 United States Department of Agriculture Natural Resources Conservation Service. “Urban Hydrology for Small Watersheds - Technical Release 55.” June 1986. Figure 2.1 United States Department of Agriculture Natural Resources Conservation Service. “Urban Hydrology for Small Watersheds - Technical Release 55.” June 1986. Figure 2.2 Asquith, W.H., 1999, Areal-reduction factors for the precipitation of the 1-day design storm in Texas: U.S. Geological Survey Water- Resources Investigations Report 99–4267, 81 p. Table 2.5 North Central Texas Council of Governments. “ISWM Technical Manual - Hydrology.”Integrated Stormwater Management. Table 2.6 North Central Texas Council of Governments. “ISWM Technical Manual - Hydrology.”Integrated Stormwater Management. Figure 3.11 Denison, Texas. “Storm Drainage System Design Manual.” Storm Drainage System Design Manual, Apr. 2017. Figure 3.26 Texas Department of Transportation. “Hydraulic Design Manual.” Hydraulic Design Manual, Oct. 2011. Figure 3.32 Low, Nathan John. “Theoretical Determination of Subcritical Sequent Depths for Complete and Incomplete Hydraulic Jumps in Closed Conduits of Any Shape.” BYU ScholarsArchive, 1 Dec. 2008. Figure 3.33 United States Department of Agriculture Natural Resources Conservation Service. “Urban Hydrology for Small Watersheds - Technical Release 55.” June 1986. Figure 3.34 United States Department of Agriculture Natural Resources Conservation Service. “Urban Hydrology for Small Watersheds - Technical Release 55.” June 1986. Figure 3.35 U.S. Department of Transportation Federal Highway Administration. “Hydraulic Design of Energy Dissipators for Culverts and Channels.” Hydraulic Engineering Circular, vol. 13, no. 3, July 2006. Figure 3.36 U.S. Department of Transportation Federal Highway Administration. “Hydraulic Design of Energy Dissipators for Culverts and Channels.” Hydraulic Engineering Circular, vol. 13, no. 3, July 2006. Figure 3.37 U.S. Department of Transportation Federal Highway Administration. “Hydraulic Design of Energy Dissipators for Culverts and Channels.” Hydraulic Engineering Circular, vol. 13, no. 3, July 2006. Figure 5.2 U.S. Department of Transportation Federal Highway Administration. “Hydraulic Design of Energy Dissipators for Culverts and Channels.” Hydraulic Engineering Circular, vol. 13, no. 3, July 2006. Figure 5.3 U.S. Department of Transportation Federal Highway Administration. “Hydraulic Design of Energy Dissipators for Culverts and Channels.” Hydraulic Engineering Circular, vol. 13, no. 3, July 2006.

146 Appendices 1 INTRODUCTION A.2.1 C Adjustment Factor Example

Example Site 2

There is a 3-acre site proposed to hold office buildings, HYDROLOGY and the developer wishes to capture the first inch of rainfall to be treated by rain gardens. The site is 90% impervious. From Table 2.3, the value is 0.90.

C 3

A.2 ROADWAY Determine the design water quality volume using the DRAINAGE DESIGN methods described in Section 2.3.3:

HYDROLOGY Determine the runoff coefficient. 4

From Table 2.3, C = 0.9 BRIDGE HYDRAULIC DESIGN Calculate the water quality capture depth.

DWQ = PWQ*C 5 DESIGN

DWQ = 1.0 in*(0.90) OPEN CHANNEL

DWQ = 0.90 in Calculate the design water quality volume. 6 DRAINAGE STORAGE DESIGN VWQ = DWQ*A 2 VWQ = 0.90 in*(1 ft)/(12 in)*3 acres* (43560 ft )/acre 3

VWQ = 9801 ft 7 Size rain gardens to hold the design water quality volume. CONTROL MEASURES EROSION & SEDIMENT Determine the adjusted C value:

Cadj = C*(1-1/2 *PWQ ) 8 Cadj = 0.90*(1-1/2*(1 in)) FLOODPLAIN & SUMP Cadj = 0.45 DESIGN REQUIREMENTS Compare pre- and post-project runoff for the 50% annual chance storm event using the adjusted C factor for proposed conditions. If the proposed runoff is higher

than existing, additional detention measures are needed 9 to contain the 50% annual chance storm event. Continue REQUIREMENTS

with detention analysis methods described in the manual OTHER REGULATORY for the 10%, 2%, and 1% annual chance storm events. 10 SUBMITTAL SUBMITTAL REQUIREMENTS 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 147 APPENDICES SAG INLET DESIGN WORKSHEET COMBINATION INLET AT LOW POINT

∆Q1 ∑Q ∆Q2

L L A.3 1 2 Q Q BP1 BP2 HYDRAULICS dA dC dB Inlet A Inlet C Inlet B

660+10 661+1 660+53 662+05 663+50 Station Station Station Station Station

Transverse Slope ST 0.02 ft/ft Shoulder Width 6 ft

Allowable Zd 12 ft Lane Width 12 ft

Allowable da 0.24 ft (dA = dC = 0.12 ft allowable)

Time of Concentration Tc 5.0 min 50 yr. Rainfall m 8.28 Coefficients n 0.587 Rainfall Intensity I 3.32 in/hr (for 5 min duration) Face of Curb Distance Between Last Inlet L 6 ft and Low Point L1 153 ft 2 W 12 ft Width of Catchment Area W1 24.5 ft 2 W 4 Q 4 0.24 cfs Bypass from Last Inlet QBP1 0.28 cfs BP2 Q 0.33 cfs Discharge of Catchment Area Q1 0.26 cfs 2

Q = Q + Q + Q + Q total BP1 1 BP2 2 L 1.1 cfs Qtotal = 0.28+0.26+0.24+0.33 = Combination or Grate Inlet for Sag P (C/G) C B See Figure 3.9 in Effective Perimeter of Grate Inlets PA 0 ft Width 0 Length 0 (reduced By 50% for Plugging) P 3.87 ft Width 1.31 Length 1.25 Manual for B Grate Dimensions PC 0 ft Width 0 Length 0

∑Q = QA + QB + QC 2 1.5 1.5 1.5 ∑Q + CWA PA(0.5da) + CWBPBdb + CWC PC(0.5dC) 1.37 cfs Capacity is Adequate, 2/3 Design is Complete ∑Q 0.21 ft Check Calculated d dB = B CWAPA0.3536 + CWBPB + CWB + CWCPC0.3536 against allowable dC

If dB < allowable dB the design is complete 3 If dB > allowable dB, additional inlets must be added and the process repeated

Notes: 1 If using a combination inlet for the sag, the flank grate inlets are nor required except in a depressed area. 2 Formulas based on weir flow. See Manual Section 3.3.3.1. 3 To add more than one outlet in the sag or flanks just increase the width and length values to the sum of all values. Inlets can be different sizes. See Figure 3.9 in Manual for grate dimensions. 4 QBP1 and QBP2 come from the inlet spreadsheet.

148 Appendices 1 INTRODUCTION A.3.1 Sag Inlet Design Worksheet

SAG INLET DESIGN WORKSHEET 2

COMBINATION INLET AT LOW POINT HYDROLOGY

∆Q1 ∑Q ∆Q2 3 L1 L2 Q Q ROADWAY BP1 BP2 DRAINAGE DESIGN

dA dC dB 4

Inlet A Inlet C BRIDGE

Inlet B HYDRAULIC DESIGN

660+10 661+1 660+53 662+05 663+50 Station Station Station Station Station 5 DESIGN OPEN CHANNEL

Transverse Slope ST 0.02 ft/ft Shoulder Width 6 ft

Allowable Zd 12 ft Lane Width 12 ft

Allowable da 0.24 ft (dA = dC = 0.12 ft allowable) 6 Time of Concentration Tc 5.0 min 50 yr. Rainfall m 8.28 DRAINAGE STORAGE DESIGN Coefficients n 0.587 Rainfall Intensity I 3.32 in/hr (for 5 min duration) Face of Curb Distance Between Last Inlet L 6 ft and Low Point L1 153 ft 2 W 12 ft 7 Width of Catchment Area W1 24.5 ft 2 W 4 Q 4 0.24 cfs Bypass from Last Inlet QBP1 0.28 cfs BP2 CONTROL MEASURES Q 0.33 cfs EROSION & SEDIMENT Discharge of Catchment Area Q1 0.26 cfs 2

Q = Q + Q + Q + Q total BP1 1 BP2 2 L 1.1 cfs Qtotal = 0.28+0.26+0.24+0.33 =

Combination or Grate Inlet for Sag P (C/G) C 8 B See Figure 3.9 in Effective Perimeter of Grate Inlets PA 0 ft Width 0 Length 0 FLOODPLAIN & SUMP (reduced By 50% for Plugging) P 3.87 ft Width 1.31 Length 1.25 Manual for DESIGN REQUIREMENTS B Grate Dimensions PC 0 ft Width 0 Length 0

∑Q = QA + QB + QC 2∑Q + C P (0.5d )1.5 + C P d 1.5 + C P (0.5d )1.5 WA A a WB B b WC C C 9 1.37 cfs Capacity is Adequate, 2/3 Design is Complete REQUIREMENTS ∑Q OTHER REGULATORY 0.21 ft Check Calculated d dB = B CWAPA0.3536 + CWBPB + CWB + CWCPC0.3536 against allowable dC 10 If dB < allowable dB the design is complete If d > allowable d , additional inlets must be added3 and the process repeated SUBMITTAL B B REQUIREMENTS

Notes: 1 If using a combination inlet for the sag, the flank grate inlets are nor required except in a depressed area. 2

Formulas based on weir flow. See Manual Section 3.3.3.1. 11 3 To add more than one outlet in the sag or flanks just increase the width and length values to the sum of all values. OPERATION & OPERATION Inlets can be different sizes. See Figure 3.9 in Manual for grate dimensions. MAINTENANCE 4 QBP1 and QBP2 come from the inlet spreadsheet.

Dallas Drainage Design Manual 149 APPENDICES A.3.2 Manning’s n for Channels

Type of Channel and Description Minimum Normal Maximum Natural streams – minor streams (top width at floodstage < 100 ft) Main Channels A. Clean, straight, full stage, no rifts or deep pools 0.025 0.030 0.033 B. Same as above, but more stones and weeds 0.030 0.035 0.040 C. Clean, winding, some pools and shoals 0.033 0.040 0.045 D. Same as above, but some weeds and stones 0.035 0.045 0.050 E. Same as above, lower stages, more ineffective slopes and sections 0.040 0.048 0.055 F. Same as “d” with more stones 0.045 0.050 0.060 G. Sluggish reaches, weedy, deep pools 0.050 0.070 0.080 H. Very weedy reaches, deep pools, or floodways with 0.075 0.100 0.150 heavy stand of timber and underbrush Mountain streams, no vegetation in channel, banks usually steep, trees and brush along banks submerged at high stages bottom: gravels, cobbles, and few boulders 0.030 0.040 0.050 bottom: cobbles with large boulders 0.040 0.050 0.070 Floodplains A. Pasture, no brush - - - 1. short grass 0.025 0.030 0.035 2. high grass 0.030 0.035 0.050 B. Cultivated areas - - - 1. no crop 0.020 0.030 0.040 2. mature row crops 0.025 0.035 0.045 3. mature field crops 0.030 0.040 0.050 C. Brush - - - 1. scattered brush, heavy weeds 0.035 0.050 0.070 2. light brush and trees, in winter 0.035 0.050 0.060 3. light brush and trees, in summer 0.040 0.060 0.080 4. medium to dense brush, in winter 0.045 0.070 0.110 5. medium to dense brush, in summer 0.070 0.100 0.160 D. Trees - - - 1. dense willows, summer, straight 0.110 0.150 0.200 2. cleared land with tree stumps, no sprouts 0.030 0.040 0.050 3. same as above, but with heavy growth of sprouts 0.050 0.060 0.080 4. heavy stand of timber, a few down trees, little undergrowth, 0.080 0.100 0.120 flood stage below branches

150 Appendices 1 INTRODUCTION Type of Channel and Description Minimum Normal Maximum 5. same as D.4 with flood stage reaching branches 0.100 0.120 0.160 2

Excavated or Dredged Channels HYDROLOGY A. Earth, straight, and uniform - - - 1. clean, recently completed 0.016 0.018 0.020

2. clean, after weathering 0.018 0.022 0.025 3 ROADWAY ROADWAY

3. gravel, uniform section, clean 0.022 0.025 0.030 DRAINAGE DESIGN 4. with short grass, few weeds 0.022 0.027 0.033 B. Earth winding and sluggish - - - 4 BRIDGE 1. no vegetation 0.023 0.025 0.030 HYDRAULIC DESIGN 2. grass, some weeds 0.025 0.030 0.033 3. dense weeds or aquatic plants in deep channels 0.030 0.035 0.040 5

4. earth bottom and rubble sides 0.028 0.030 0.035 DESIGN OPEN CHANNEL 5. stony bottom and weedy banks 0.025 0.035 0.040 6. cobble bottom and clean sides 0.030 0.040 0.050

C. Dragline-excavated or dredged - - - 6 DRAINAGE

1. no vegetation 0.025 0.028 0.033 STORAGE DESIGN 2. light brush on banks 0.035 0.050 0.060 D. Rock cuts - - -

1. smooth and uniform 0.025 0.035 0.040 7 CONTROL MEASURES 2. jagged and irregular 0.035 0.040 0.050 EROSION & SEDIMENT E. Channels not maintained, weeds and brush uncut - - - 1. dense weeds, high as flow depth 0.050 0.080 0.120

2. clean bottom, brush on sides 0.040 0.050 0.0800 8 3. same as above, highest stage of flow 0.045 0.070 0.110 FLOODPLAIN & SUMP DESIGN REQUIREMENTS 4. dense brush, high stage 0.080 0.100 0.140 Lined or Constructed Channels - - - A. Cement - - - 9 1. neat surface 0.010 0.011 0.013 REQUIREMENTS 2. mortar 0.011 0.013 0.015 OTHER REGULATORY B. Wood - - -

1. planed, untreated 0.010 0.012 0.014 10 SUBMITTAL SUBMITTAL

2. planed, creosoted 0.011 0.012 0.015 REQUIREMENTS 3. unplaned 0.011 0.013 0.015 4. plank with battens 0.012 0.015 0.018 11

5. lined with roofing paper 0.010 0.014 0.017 & OPERATION MAINTENANCE

Dallas Drainage Design Manual 151 APPENDICES Type of Channel and Description Minimum Normal Maximum C. Concrete - - - 1. trowel finish 0.011 0.013 0.015 2. float finish 0.013 0.015 0.016 3. finished, with gravel on bottom 0.015 0.017 0.020 4. unfinished 0.014 0.07 0.020 5. gunite, good section 0.016 0.019 0.023 6. gunite, wavy section 0.018 0.022 0.025 7. on good excavated rock 0.017 0.020 - 8. on irregular excavated rock 0.022 0.027 - D. Concrete bottom float finish with sides of: - - - 1. dressed stone in mortar 0.015 0.017 0.020 2. random stone in mortar 0.017 0.020 0.024 3. cement rubble masonry, plastered 0.016 0.020 0.024 4. cement rubble masonry 0.020 0.025 0.030 5. dry rubble or riprap 0.020 0.030 0.035 E. Gravel bottom with sides of: - - - 1. formed concrete 0.017 0.020 0.025 2. random stone mortar 0.020 0.023 0.026 3. dry rubble or riprap 0.023 0.033 0.036 F. Brick - - - 1. glazed 0.011 0.013 0.015 2. in cement mortar 0.012 0.015 0.018 G. Masonry - - - 1. cemented rubble 0.017 0.025 0.030 2. dry rubble 0.023 0.032 0.035 H. Dressed ashlar/stone paving - - - I. Asphalt - - - 1. smooth 0.013 0.013 - 2. rough 0.016 0.016 - J. Vegetal lining 0.030 - 0.500

152 Appendices 1 INTRODUCTION A.3.3 Manning’s n for Closed Conduits Flowing Partly Full 2

Type of Conduit and Description Minimum Normal Maximum HYDROLOGY A. Brass, smooth 0.009 0.010 0.013 B. Steel - - -

1. Lockbar and welded 0.010 0.012 0.014 3 ROADWAY ROADWAY

2. Riveted and spiral 0.013 0.016 0.017 DRAINAGE DESIGN C. Cast Iron - - - 1. Coated 0.010 0.013 0.014 4 BRIDGE 2. Uncoated 0.011 0.014 0.016 HYDRAULIC DESIGN E. Wrought Iron - - - 1. Black 0.012 0.014 0.015 5

2. Galvanized 0.013 0.016 0.017 DESIGN OPEN CHANNEL F. Corrugated Metal - - - 1. Subdrain 0.017 0.019 0.021

2. Stormdrain 0.021 0.024 0.030 6 DRAINAGE

G. Cement - - - STORAGE DESIGN 1. Neat Surface 0.010 0.011 0.013 2. Mortar 0.011 0.013 0.015

H. Concrete - - - 7 CONTROL MEASURES 1. Culvert, straight and free of debris 0.010 0.011 0.013 EROSION & SEDIMENT 2. Culvert with bends, connections, and some debris 0.011 0.013 0.014 3. Finished 0.011 0.012 0.014

4. Sewer with manholes, inlet, etc., straight 0.013 0.015 0.017 8 5. Unfinished, steel form 0.012 0.013 0.014 FLOODPLAIN & SUMP DESIGN REQUIREMENTS 6. Unfinished, smooth wood form 0.012 0.014 0.016 7. Unfinished, rough wood form 0.015 0.017 0.020 I. Wood - - - 9 1. Stave 0.010 0.012 0.014 REQUIREMENTS 2. Laminated, treated 0.015 0.017 0.020 OTHER REGULATORY J. Clay - - -

1. Common drainage tile 0.011 0.013 0.017 10 SUBMITTAL SUBMITTAL

2. Vitrified sewer 0.011 0.014 0.017 REQUIREMENTS 3. Vitrified sewer with manholes, inlet, etc. 0.013 0.015 0.017 4. Vitrified Subdrain with open joint 0.014 0.016 0.018 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 153 APPENDICES Type of Conduit and Description Minimum Normal Maximum K. Brickwork - - - 1. Glazed 0.011 0.013 0.015 2. Lined with cement mortar 0.012 0.015 0.017 3. Sanitary sewers coated with sewage slime with bends 0.012 0.013 0.016 and connections 4. Paved invert, sewer, smooth bottom 0.016 0.019 0.020 5. Rubble masonry, cemented 0.018 0.025 0.030

154 Appendices 1 INTRODUCTION A.3.4 Gutter Flow / Inlet Computations 5/2 2 HYDROLOGY - (a) 5/2 3 Remarks ROADWAY ROADWAY DRAINAGE DESIGN ( ) Carry over to: L 4 cfs BRIDGE QI-Qa HYDRAULIC DESIGN QI cfs 5 QI/QA DESIGN OPEN CHANNEL a/y La/Lr 6 DRAINAGE ft La STORAGE DESIGN ft Lr y qI Capture per foot of inlet with 100% interception= 0.7 (a+y) Lr Required inlet for 100% interception= Qa La QI/QA Actual inlet length From ﬁgure (10) QI Actual Inlet Interception q qL cfs/ft 7 a ft CONTROL MEASURES EROSION & SEDIMENT w ft y ft GUTTER FLOW / INLET COMPUTATIONS s 8 ft/ft n FLOODPLAIN & SUMP DESIGN REQUIREMENTS z 3/8 1/2 Qa cfs CO cfs 9 ( ) Q cfs REQUIREMENTS OTHER REGULATORY OTHER REGULATORY No. D.A. 10 SUBMITTAL SUBMITTAL REQUIREMENTS LOCATION INLET ID Q CO Discharge calculated for DA Qa Carryover from upstream inlet z Actual discharge= Q+CO n Reciprocal of cross slope s (can use average slope equivalent for parabolic crown) roughness (0.0175 normal) Manning’s y Gutter slope Gutter depth of ﬂow= Qa 0.56 (z/n) s 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 155 APPENDICES A.3.5 Full Flow Coefficient Values A.3.5.1 Elliptical Concrete Pipe

Pipe Size Approximate A Area R Hydraulic Value of C = 1.486/n x A x R2/3 R =S (HE) Equivalent (Square Feet) Radius (Feet) 1 S = R (VE) (Inches) Circular Diameters n = 0.010 n = 0.011 n = 0.012 n = 0.013 (Inches) 14 x 23 18 1.8 0.367 138 125 116 108 19 x 30 24 3.3 0.490 301 274 252 232 22 x 34 27 4.1 0.546 405 368 339 313 24 x 38 30 5.1 0.613 547 497 456 421 27 x 42 33 6.3 0.686 728 662 607 560 29 x 45 36 7.4 0.736 891 810 746 686 32 x 49 39 8.8 0.812 1,140 1,036 948 875 34 x 53 42 10.2 0.875 1,386 1,260 1,156 1,067 38 x 60 48 12.9 0.969 1,878 1,707 1,565 1,445 43 x 68 54 16.6 1.106 2,635 2,395 2,196 2,027 48 x 76 60 20.5 1.229 3,491 3,174 2,910 2,686 53 x 83 66 24.8 1.352 4,503 4,094 3,753 3,464 58 x 91 72 29.5 1.475 5,680 5,164 4,734 4,370 63 x 98 78 34.6 1.598 7,027 6,388 5,856 5,406 68 x 106 84 40.1 1.721 8,560 7,790 7,140 6,590 72 x 113 90 46.1 1.845 10,300 9,365 8,584 7,925 77 x 121 96 52.4 1.967 12,220 11,110 10,190 9,403 82 x 128 102 59.2 2.091 14,380 13,070 11,980 11,060 87 x 136 108 66.4 2.215 16,770 15,240 13,970 12,900 92 x 143 114 74.0 2.340 19,380 17,620 16,150 14,910 97 x 151 120 82.0 2.461 22,190 20,180 18,490 17,070 106 x 166 132 99.2 2.707 28,630 26,020 23,860 22,020 116 x 180 144 118.6 2.968 36,400 33,100 30,340 28,000

156 Appendices 1 INTRODUCTION

A.3.5.2 Concrete Arch Pipe 2 HYDROLOGY

Pipe Size R x S Approximate A Area R Hydraulic Value of C = 1.486/n x A x R2/3 (Inches) Equivalent (Square Feet) Radius (Feet) 1 Circular Diameters n = 0.010 n = 0.011 n = 0.012 n = 0.013 (Inches) 3 ROADWAY ROADWAY

11 x 18 15 1.1 0.25 65 59 54 50 DRAINAGE DESIGN 131/2 x 22 18 1.6 0.30 110 100 91 84 151 x 26 21 2.2 0.36 165 150 137 127 4 18 x 281/2 24 2.8 0.45 243 221 203 187 BRIDGE HYDRAULIC DESIGN 221/2 x 361/4 30 4.4 0.56 441 401 368 339 265/8 x 433/4 36 6.4 0.68 736 669 613 566 5

315/18 x 511/8 42 8.8 0.80 1,125 1,023 938 866 DESIGN OPEN CHANNEL 36 x 581/2 48 11.4 0.90 1,579 1,435 1,315 1,214 40 x 65 54 14.3 1.01 2,140 1,945 1,783 1,646

45 x 73 60 17.7 1.13 2,851 2,592 2,376 2,193 6 DRAINAGE

54 x 88 72 25.6 1.35 4,641 4,219 3,867 3,569 STORAGE DESIGN 63 x102 84 34.6 1.57 6,941 6,310 5,784 5,339 72 x 115 90 44.5 1.77 9,668 8,789 8,056 7,436 1/4 77 x 122 96 51.7 1.92 11,850 10,770 9,872 91,122 7 871/8 x 138 108 66.0 2.17 16,430 14,940 13,690 12,640 CONTROL MEASURES EROSION & SEDIMENT 967/8 x 154 120 81.8 2.42 21,975 19,977 18,312 16,904 1061/2 x 1683/4 132 99.1 2.65 28,292 25,720 23,577 21,763 8 FLOODPLAIN & SUMP DESIGN REQUIREMENTS 9 REQUIREMENTS OTHER REGULATORY OTHER REGULATORY 10 SUBMITTAL SUBMITTAL REQUIREMENTS 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 157 APPENDICES A.3.5.3 Precast Concrete Box Section

Box Size A Area R Hydraulic Box Size A Area R Hydraulic Value of C1 = Value of C1 = Span x (Square Radius 1.486/n x A x R2/3 Span x Rise (Square Radius (Feet) 1.486/n x A x R2/3 Rise (Feet) Feet) (Feet) (Feet) Feet) n = 0.012 n = 0.013 n = 0.012 n = 0.013 3 x 2 5.78 0.63 524 484 9 x 5 43.88 1.67 7,060 7,070 3 x 3 8.78 0.78 923 852 9 x 6 52.88 1.87 9,950 9,180 4 x 2 7.65 0.69 743 686 9 x 7 61.88 2.05 12,400 11,400 4 x 3 11.65 0.90 1,340 1,240 9 x 8 70.88 2.20 14,800 13,700 4 x 4 15.65 1.04 1,990 1,840 9 x 9 79.88 2.33 17,400 16,100 5 x 3 14.50 0.98 1,770 1,630 10 x 5 48.61 1.73 8,690 8,020 5 x 4 19.50 1.16 2,660 2,460 10 x 6 58.61 1.95 11,300 10,462 5 x 5 24.50 1.30 3,620 3,340 10 x 7 68.61 2.14 14,100 13,000 6 x 3 17.32 1.04 2,200 2,030 10 x 8 78.61 2.31 17,000 15,700 6 x 4 23.32 1.25 3,350 3,100 10 x 9 88.61 2.46 20,000 18,500 6 x 5 29.32 1.42 4,590 4,240 10 x 10 98.61 2.59 23,000 21,300 6 x 6 35.32 1.56 5,880 5,430 11 x 4 42.32 1.52 6,930 6,390 7 x 4 27.11 1.33 4,050 3,740 11 x 6 64.32 2.02 12,730 11,700 7 x 5 34.11 1.52 5,590 5,160 11 x 8 86.32 2.41 19,200 17,700 7 x 6 41.11 1.68 7,200 6,650 11 x 10 108.32 2.72 26,100 24,100 7 x 7 48.11 1.82 8,880 8,200 11 x 11 119.32 2.85 29,700 27,400 8 x 4 31.11 1.39 4,790 4,420 12 x 4 46.00 1.55 7,630 7,050 8 x 5 39.11 1.60 6,630 6,120 12 x 6 70.00 2.08 14,100 13,000 8 x 6 47.11 1.78 8,760 7,920 12 x 8 94.00 2.50 21,400 19,800 8 x 7 55.11 1.94 10,600 9,790 12 x 10 118.00 2.83 29,300 27,000 8 x 8 63.11 2.07 12,700 11,700 12 x 12 142.00 3.11 37,500 34,600

158 Appendices 1

A.3.5.4 Circular Concrete Pipe INTRODUCTION 2 HYDROLOGY D Pipe A Area R Hydraulic Value of C = 1.486/n x A x R2/3 Diameter (Square Feet) Radius (Feet) 1 (Inches) n = 0.010 n = 0.011 n = 0.012 n = 0.013

8 0.349 0.167 15.8 14.3 13.1 12.1 3 ROADWAY ROADWAY

10 0.545 0.208 28.4 25.8 23.6 21.8 DRAINAGE DESIGN 12 0.785 0.205 46.4 42.1 38.6 35.7 15 1.227 0.312 84.1 76.5 70.1 64.7 4

18 1.767 0.375 137 124 114 105 BRIDGE

21 2.405 0.437 206 187 172 158 HYDRAULIC DESIGN 24 3.142 0.500 294 267 245 226 27 3.976 0.562 402 366 335 310 5 30 4.909 0.625 533 485 444 410 DESIGN OPEN CHANNEL 33 5.940 0.688 686 624 574 530 36 7.069 0.750 867 788 722 666

42 9.621 0.875 1,308 1,189 1,090 1,006 6 DRAINAGE

48 12.566 1.000 1,867 1,698 1,556 1,436 STORAGE DESIGN 54 15.904 1.125 2,557 2,325 2,131 1,967 60 19.635 1.250 3,385 3,077 2,821 2,604

66 23.758 1.375 4,364 3,967 3,636 3,357 7

72 28.274 1.500 5,504 5,004 4,587 4,234 CONTROL MEASURES EROSION & SEDIMENT 78 33.183 1.625 6,815 6,195 5,679 5,242 84 38.485 1.750 8,304 7,549 6,920 6,388 90 44.170 1.875 9,985 9,078 8,321 7,684 8 96 50.266 2.000 11,850 10,780 9,878 9,119 FLOODPLAIN & SUMP

102 56.745 2.125 19,340 12,670 11,620 10,720 DESIGN REQUIREMENTS 108 63.617 2.250 16,230 14,760 13,530 12,490 114 70.882 2.375 18,750 17,040 15,620 14,420

120 78.540 2.500 21,500 19,540 17,920 16,540 9

126 86.590 2.625 24,480 22,260 20,400 18,830 REQUIREMENTS OTHER REGULATORY OTHER REGULATORY 132 95.033 2.750 27,720 25,200 23,100 21,330 138 103.870 2.875 31,210 28,370 26,010 24,010

144 113.100 3.000 34,960 31,780 29,130 26,890 10 SUBMITTAL SUBMITTAL REQUIREMENTS 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 159 APPENDICES A.3.6 Energy Equations in Open A.3.6.2 Specific Energy Channels The specific energy of flow in a channel section is defined as the energy per pound of water measured with respect to the channel bottom. Specific energy,E (expressed as A.3.6.1 Energy head in feet), is given by the following: Conservation of energy is a basic principal in open channel 2 2 2 flow. As shown in Figure A.3.1, the total energy at a given E = y+ V /2g=y+ (Q /(2gA )) (Equation A.3.3) location in an open channel is expressed as the sum of the potential energy head (elevation), pressure head, and y = depth (ft) kinetic energy head (velocity head). The total energy at V = mean velocity (ft) given channel cross section can be represented as: g = gravitational acceleration = 32.2 ft/s2 2

Et=Z+y+ (V /2g) (Equation A.3.1) Q = discharge (cfs) total energy (ft) Et = A = area of channel cross section (ft2) Z = elevation above given datum (ft) y = flow depth (ft) A.3.6.3 Froude Number

V = mean velocity (ft) The influence of gravity on fluid motion in open channel flow can be expressed in a dimensionless quantity called g = gravitational acceleration = 32.2 ft/s2 a Froude Number (Fr). The Froude Number is expressed in the following equation.

Written between an upstream cross section designated 1 ____V and a downstream cross section designated 2, the energy Fr= _ (Equation A.3.4) equation becomes the following: √ gd V = mean velocity (ft/s) Z + y + (V 2)/2g= Z + y + (V 2)/2g+ h (Equation 1 1 1 2 2 2 L acceleration of gravity 32.2 ft/s2 A.3.2) g = = d = hydraulic depth (ft) head or energy loss between Section 1 and 2 (ft) hL = The hydraulic depth is defined as the cross sectional area of the channel perpendicular to the flow divided by the The terms in the energy equation are illustrated in free water surface topwidth. Figure A.3.1. The energy equation states that the total energy head at an upstream cross section is equal to the total energy head at a downstream section plus the energy head loss between the two sections.

Figure A.3.1 Shallow Concentrated Flow Average Velocity Total Energy Line Energy Gradient 2 h V1 2g L Water Surface 2 V2 2g 1 Flow Specific Energy

Channel ottom 2 Total Energy Head Total

1 2 Datum Section 1 Section 2

160 Appendices 1 INTRODUCTION 2 HYDROLOGY 3

A.4 A.5 ROADWAY DRAINAGE DESIGN PROCEDURES SUBMITTAL 4

All complaints must be entered into the Customer Service REQUIREMENTS AND BRIDGE

Request (CSR) / 311 system and they will be addressed in HYDRAULIC DESIGN accordance with the department service level agreements. FORMS 5 DESIGN

A.5.1 Checklist for Storm Drainage OPEN CHANNEL Plans Drainage Area Map 6

1. Use 1”=200’ scale for onsite and 1”=400’ for creeks DRAINAGE

off site and show match lines between any two or STORAGE DESIGN more maps.

2. Show existing and proposed storm drains and inlets.

3. Indicate subareas for each alley, street, and offsite area. 7 CONTROL MEASURES 4. Indicate contours on map for on and offsite. EROSION & SEDIMENT

5. Use design criteria as shown in design manual.

6. Indicate zoning on drainage area.

7. Show points of concentration. 8 FLOODPLAIN & SUMP

8. Indicate runoff at all inlets, dead-end streets and DESIGN REQUIREMENTS alleys, or to adjacent additions or acreage.

9. Provide runoff calculations for all areas showing acreage, runoff coefficient, inlet time. 9 10. For cumulative runoff, show calculations. REQUIREMENTS OTHER REGULATORY OTHER REGULATORY 11. Indicate all crests, sags, and street and alley intersections with flow arrows.

12. Identify direction of north. 10 SUBMITTAL SUBMITTAL 13. Show limits of 1% annual chance floodplain on drainage REQUIREMENTS area map. 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 161 APPENDICES Plan, Profile, and Detail Sheets 21. Show details of all junction boxes, headwalls on storm 1. Show plan and profile of all storm drains. drain, flumes, and manholes when more than one pipe intersects the manhole or any other item not a 2. Specify Class III pipe unless otherwise noted in profile. standard detail.

3. Provide inlets where street capacity is exceeded. 22. All Y-inlets and inlets 10 ft or greater have a min 21” Provide inlets where alley runoff exceeds intersecting lateral and all smaller inlets have a min 18” lateral. street capacity. 23. Provide headwalls for all storm drains at outfall. 4. Indicate property lines along storm drainage and show easements with dimensions. 24. Check the need for curbing at all alley turns and “T” intersections. Flatten grades ahead of turns 5. Show all existing utilities in plan and profile of storm and intersections. drains with elevations. 25. Calculate hydraulic grade line for laterals and inlets 6. Indicate existing and proposed ground line and to ensure collection of storm water. For inlets, provide improvements on all street, alley, and storm drain profiles. HGL on profile for all profiled laterals with hydraulic data. Laterals longer than 80 feet require special 7. Show all hydraulics, velocity head changes, gradients, analysis. computations, and profile outfall with typical section and computations. 26. Where inlets are placed in alley, provide curbing for 10 feet on each side of inlet and on other side of alley, 8. Show laterals on trunk profile with stations. where the top of inlet elevation is even with the high edge of alley pavement. The width between curbs 9. Indicate size of inlet on plan view, lateral size and flow shall be equal to or greater than 10 feet. line, paving station and top-of-curb elevation. 27. Use standard curb inlets in streets and alleys. Use 10. Indicate runoff concentrating at all inlets and recessed inlets in divided streets. Do not use grate or direction of flow. Show runoff for all stub outs, pipes, curb and grate inlet unless other solution is not available. and intakes. 28. Provide 7 ½-inch curb on alleys parallel to creek or 11. Show future streets and grades where applicable. channel on creek side of alley.

12. Do not use 90-degree turns on storm drains or outfall. 29. Indicate flow line elevations of storm drains on profile, Provide good alignment with junction structures or show percent grade. Match top inside of pipe where manholes (for small systems). adjacent to other size pipe.

13. Discharge storm drains at the flow line of creeks and 30. Where laterals tie into trunk line, channel or creek, channels unless competent rock is present. place at 60 degree angle with centerlines. Connect 14. Show water surface at outfall of storm drain. them so that the longitudinal centers intersect.

15. Where fill is proposed for trench cut in creeks or 31. Show curve data for all storm drains. outfall ditches, specify compacted fill. 32. Tie storm drain stationing with paving stations.

16. Use Y-inlets in ditches. 33. Do not flow storm water from streets into alleys.

17. Where connections are made to existing storm drain, 34. On all dead-end streets and alleys, show grade out for show computations of existing system when available. drainage on the profiles and provide erosion control.

18. Show pipe sizes in plan and profile. 35. Specify concrete strength for all structures. The 19. Provide separate plan and profile for both storm drain minimum allowable is 3600 psi and paving plans. The storm drain pipes should also 36. Where quantities of runoff are shown on plan or be shown on paving plans with a dashed line. profile, indicate storm frequency design.

20. Use heavier than Class III pipes where crossing 37. Provide sections for road, railroad, and other ditches railroads, deep fill, and heavy loads. with profiles and hydraulic computations. Show design water surface on profile.

162 Appendices 1

38. Investigation shall be made by the engineer to Bridges INTRODUCTION validate the adequacy of the storm drain outfall. 1. Clear the lowest member of the bridges by 2 feet

39. Do not use high velocities in storm drain design. above the design water surface unless otherwise 2

Maximum discharge velocity should not exceed 6 ft/s directed by the City. HYDROLOGY at outfall. 2. Show geotechnical soil boring information on plans. 40. Flumes may not be allowed unless specifically designated. 3. Show bridge sections upstream and downstream. 3 ROADWAY ROADWAY 41. If time of concentration is different, provide the 4. Provide hydraulic calculations on all sections. DRAINAGE DESIGN calculation for inlet time and pipe travel time. 5. Provide structural details and calculations with dead 42. Provide lateral profiles for laterals exceeding 12 ft load deflection diagram.

in length. 4 6. Provide vertical and horizontal alignment. BRIDGE 43. Proposed driveway turnouts must be 10 feet from any 7. Provide drainage area map and show all HYDRAULIC DESIGN existing or proposed inlet. computations for runoff affecting a detention basin. 44. Do not use bends for pipe sizes less than 30-inch 8. Provide a plot plan with existing and proposed diameter unless specifically authorized by the Director. 5

contours for a detention basin and plan for structural DESIGN Statements measures. OPEN CHANNEL

1. Any offsite drainage work or discharge to downstream 9. Where earth embankment is proposed for property will require a letter of permission or impoundment, furnish a typical embankment section easements. Submit field notes for offsite easement and specifications for fill; include profile for the 6 structural outfall structure and geotechnical report. DRAINAGE

that may be required. STORAGE DESIGN

2. Provide written statement signed by a Professional 10. Provide structural details and calculations for any Engineer acknowledging that he/she has analyzed item and geotechnical report not a standard detail. the proposed storm drainage outfall effects on

11. Provide detention basin volume calculations and 7 the adjoining property, and that the discharge will elevations versus storage curve. not adversely affect or jeopardize this property. CONTROL MEASURES Provide letter of acceptance from adjoining property 12. Provide hydraulic calculations for outflow structure and EROSION & SEDIMENT owner, if post-development discharges exceed pre- elevation versus discharge curve for a detention basin. development rates (Development Only). 13. Provide unit hydrograph routings, or modified 3. Check for escarpment area restrictions. If in rational, where permitted for 100 acres or less for a Geologically Similar Areas, design in accordance with detention basin. 8 escarpment ordinance. FLOODPLAIN & SUMP DESIGN REQUIREMENTS 9 REQUIREMENTS OTHER REGULATORY OTHER REGULATORY 10 SUBMITTAL SUBMITTAL REQUIREMENTS 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 163 APPENDICES A.5.2 Non-Standard Material Agreement Template

AGREEMENT CITY OF DALLAS NON-STANDARD MATERIALS FOR CONSTRUCTION WITHIN PUBLIC RIGHT-OF-WAY

PROJECT: LOCATION: DESCRIPTION: MATERIAL:

The work described above is proposed for construction in the public right-of-way. The plans have been reviewed by the Building Inspection Department and the Proposed Improvements are approved subject to the following conditions: 1 All construction must conform to the requirements of the Public Works Department standard construction details and the standard specifications for Public Works construction. 2 The owner accepts full responsibility for all maintenance and the replacement of the sidewalk surface, setting bed, and concrete base including those instances when the city or utility company, in the discharge of its responsibilities, removes any portion of these improvements. All improvements located in the public right-of-way are there at the pleasure of the city and must be maintained to the satisfaction of the city. 3 All sidewalks must be constructed barrier-free to the handicapped. 4 Traffic signs and signals must not be altered unless approved by the Department of Transportation. 5 Obtain driveway/sidewalk permits from Building Inspection at 320 E. Jefferson Blvd., Room 118, 948-4480, 948- 4173, 948-4174.

The owner’s attention is directed to Sections 43-33 and 43-44 of the city code which specifies the property owner’s responsibility and liability for all claims or damages resulting from injury of loss due to the abutting sidewalk or curbs. Approval of plans by the Building Inspection Department does not change or assume any of the property owner’s responsibility. The agreement is binding upon the owner, heirs, successors or his assigns. The owner will execute this agreement in duplicate and return both copies to the Building Inspection Department for approval. One signed copy will be forwarded to the owner. Execution of this agreement by the owner signifies acceptance of all provisions and willingness to comply.

164 Appendices 1 INTRODUCTION 2 HYDROLOGY

OWNER’S NAME (PRINT) 3 ROADWAY ROADWAY

MAILING ADDRESS DRAINAGE DESIGN CITY, STATE

4 Street address (site) Lot Block BRIDGE HYDRAULIC DESIGN

SIGNED: DATE: 5 DESIGN

(Property Owner) (Title) OPEN CHANNEL

PRINTED NAME: 6 DRAINAGE

SUBSCRIBED AND SWORN TO, BEFORE ME, THIS DAY OF 20 . STORAGE DESIGN

On this day personally appeared , 7 CONTROL MEASURES known to me to be the person whose name is subscribed to the foregoing instrument and acknowledged to me that he EROSION & SEDIMENT executed the same for the purposes and consideration herein expressed.

SEAL 8 NOTARY PUBLIC FLOODPLAIN & SUMP DESIGN REQUIREMENTS APPROVED BY THE CITY OF DALLAS:

DATE: 9

BUILDING OFFICIAL REQUIREMENTS OTHER REGULATORY OTHER REGULATORY 10 SUBMITTAL SUBMITTAL REQUIREMENTS 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 165 APPENDICES PRINTED NAME:

SUBSCRIBED AND SWORN TO, BEFORE ME, THIS DAY OF 20 .

On this day personally appeared , known to me to be the person whose name is subscribed to the foregoing instrument and acknowledged to me that he executed the same for the purposes and consideration herein expressed.

SEAL NOTARY PUBLIC

166 Appendices 1 INTRODUCTION 2 HYDROLOGY 3

A.6 ROADWAY DRAINAGE DESIGN OTHER 4 BRIDGE HYDRAULIC DESIGN 5 DESIGN OPEN CHANNEL 6 DRAINAGE STORAGE DESIGN 7 CONTROL MEASURES EROSION & SEDIMENT 8 FLOODPLAIN & SUMP DESIGN REQUIREMENTS 9 REQUIREMENTS OTHER REGULATORY OTHER REGULATORY 10 SUBMITTAL SUBMITTAL REQUIREMENTS 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 167 APPENDICES No unvegetated area shall exceed 10 square feet in order to limit erosion. Additional Notes No unvegetated area shall exceed 10 square feet in order to limit erosion. No unvegetated area shall exceed 10 square feet in order to limit erosion. Seed applied uniformly with: Cyclone, Drill, Cultipacker Hydroseed (slurry with Seeder, & binder), or seed, fertilizer, hydraulic mulch with seed. Seed Mixes: Spring (March 1st - May 15th until it gets hot and rain stops) or Fall (September 1st - November 15th) Installation Seed applied uniformly with: Cyclone, Drill, Cultipacker Hydroseed (slurry with Seeder, & binder), or seed, fertilizer, hydraulic mulch with seed. Seed Mixes: Spring (March 1st - May 15th until it gets hot and rain stops) or Fall (September 1st - November 15th) Seed applied uniformly with: Cyclone, Drill, Cultipacker Hydroseed (slurry with Seeder, & binder), or seed, fertilizer, hydraulic mulch with seed. Seed Mixes: Spring (March 1st - May 15th until it gets hot and rain stops); overseed: Winter (November 1st - February) Maintenance Mow two times per year: July 1st and in (January dead of Winter 1st) to no shorter than 8 inches in height. Bag and remove from site all clippings a n d t r i m mSee also: Maintenance i n g s . List #1 Mow two times per year: July 1st and in (January dead of Winter 1st) to no shorter than 8 inches in height. Bag and remove from site all clippings and trimmings. See also: Maintenance List #1 Mow two times per year: July 1st and in (January dead of Winter 1st) to no shorter than 8 inches in height. Bag and remove from site all clippings a n d t r i m mSee also: Maintenance i n g s . List #1 Recommended Materials* Seed Mix #1 - Bottom & Sides and Seed Mix #2 - Bottom Nurse Crop Seed for winter - temporary (if seed Mixes #1 & 2 installation windows are missed) Seed Mix #1 - Bottom & Sides and winter overseed of Seed Mix #4 - Bottom Seed Mix #1 - Bottom & Sides, Seed Mix #2 - Bottom, Seed Mix #3 - Upper Slopes and Dry Side of Bank, Nurse Crop Seed for winter - temporary (if seed Mixes #1, 2 & 3 installation windows a r e m i s s e d ) Soil Preparation or Media Topsoil with Topsoil minimum 5% organic content: bladed and ripped for interface into subbase soils with Topsoil minimum 5% organic content: bladed and ripped for interface into subbase soils Topsoil with Topsoil minimum 5% organic content: bladed and ripped for interface into subbase soils Application Open Channels Open Channels with Regular Drainage or Seepage Detention Pond A.6.1 Materials Matrix The following are permissible, not exclusive. * Seed mixes and plant lists can be found on following pages

168 Appendices 1 INTRODUCTION 2 HYDROLOGY 3 ROADWAY ROADWAY DRAINAGE DESIGN 4 BRIDGE HYDRAULIC DESIGN Additional Notes No unvegetated area shall exceed 10 square feet in order to limit erosion. No unvegetated area shall exceed 9 square feet in order to limit erosion. Use of fertilizers, fungicides, herbicides and pesticides are prohibited without approval Organic alternatives may from the Director. be used. Hand pull weeds early in growth stage, before they set seed - critical in first 3 years until plantings establish. Maintain 3 inch mulch topdressing with rough/coarse cut mulch. No unvegetated area shall exceed 9 square feet in order to limit erosion. Use of fertilizers, fungicides, herbicides and pesticides are prohibited without approval Organic alternatives may from the Director. be used. Hand pull weeds early in growth stage, before they set seed - critical in first 3 years until plantings establish. Maintain 3 inch mulch topdressing with rough/coarse cut mulch. - 5 DESIGN OPEN CHANNEL 6 DRAINAGE STORAGE DESIGN Installation Seed applied uniformly with: Cyclone, Drill, Cultipacker Hydroseed (slurry with Seeder, & binder), or seed, fertilizer, hydraulic mulch with seed. Seed Mixes: Spring (March 1st - May 15th) or Fall (Sept. 1st 15) if regular rain and up Nov. until 8 weeks before average frost date 7 CONTROL MEASURES EROSION & SEDIMENT 8 Maintenance Mow two times per year: July 1st and in (January dead of Winter 1st) to no shorter than 3 i n cSee also: Maintenance h e s List #1 i n h e i g h t . Maintenance List #1 Maintenance List #1 Maintenance List #1 FLOODPLAIN & SUMP DESIGN REQUIREMENTS 9 REQUIREMENTS Recommended Materials* Seed Mix #5 Nurse Crop Seed for winter - temporary (if seed Mix #5 installation w i n d o w i s m i s s e d ) Plant List #2 Plant List #2 Plant List #2 OTHER REGULATORY OTHER REGULATORY 10 SUBMITTAL SUBMITTAL REQUIREMENTS Soil Preparation or Media Topsoil with Topsoil minimum 5% organic ripped content: or bladed for interface into subbase soils Rain Garden Planting Soil/ Amended Soils or Bioretention Soil Mix #1 Bioretention Soil Mix #1 Bioretention Soil Mix #1 11 OPERATION & OPERATION MAINTENANCE Application Service Access/ Maintenance Ramps or Pedestrian Access Slopes Rain Gardens Bioretention Tree-box filters * Seed mixes and plant lists can be found on following pages

Dallas Drainage Design Manual 169 APPENDICES Additional Notes If Porous Grass Turf Paving: No If Porous Grass Turf unvegetated area shall exceed 9 square feet in order to limit erosion. - - No unvegetated area shall exceed 10 square feet in order to limit erosion. No unvegetated area shall exceed 9 square feet in order to limit erosion. Installation Seed applied uniformly with: Cyclone, Drill, Cultipacker Hydroseed (slurry with Seeder, & binder), or seed, fertilizer, hydraulic mulch with seed. Seed Mixes: Spring (March 1st - May 15th until it gets hot and rain stops) or Fall (September 1st - November 15th) Maintenance Maintenance List #1 Maintenance List #1 Maintenance List #1 Maintenance List #1 Maintenance List #1 Maintenance List #1 Recommended Materials* Sod or Seed Mix #5 Seed Mix #5 if grass is added Plant List #4 - Aquatic Bench, Low Marsh, and High Marsh Zone, Plant List #5 - Wetland Plants, Plant List #7 - Wooded Vegetation Seed Mix #1 - Bottom & Sides and Seed Mix #2 - Bottom Nurse Crop Seed for winter - temporary (if seed Mixes #1 & 2 installation windows are missed) Plant List #2 Soil Preparation or Media Base Course #1 Base Media #1 Pond Liner Base #1, Aquatic Bench Media #1 Topsoil with Topsoil minimum 5% organic content: bladed and ripped for interface into subbase soils Bioretention Soil Mix #1 Reservoir Course #1 Application Porous Pavements Sand and organic media filters Stormwater Ponds Bioswales Bioretention Swales Permeable Unit Pavements * Seed mixes and plant lists can be found on following pages

170 Appendices 1 INTRODUCTION 2 HYDROLOGY 3 ROADWAY ROADWAY DRAINAGE DESIGN 4 BRIDGE HYDRAULIC DESIGN Additional Notes - 5 DESIGN OPEN CHANNEL 6 DRAINAGE STORAGE DESIGN Installation 7 CONTROL MEASURES EROSION & SEDIMENT 8 Maintenance Maintenance List #1 FLOODPLAIN & SUMP DESIGN REQUIREMENTS 9 REQUIREMENTS Recommended Materials* Plant List #3 - Deep Zone, Plant Water List #4 - Aquatic Bench, Low Marsh, and High Marsh Zone, Plant List #6 Zone - Semi-Wet Plant List #7 - Vegetation Wooded OTHER REGULATORY OTHER REGULATORY 10 SUBMITTAL SUBMITTAL REQUIREMENTS Soil Preparation or Media 11 OPERATION & OPERATION MAINTENANCE Application Constructed Wetlands * Seed mixes and plant lists can be found on following pages

Dallas Drainage Design Manual 171 APPENDICES A.6.2 Media

Bioretention Soil Mix #1 Material Percentage (%) Screened Cushion Sand ≥ 25 Expanded Shale 25 Fully Mature "Finished" ≤ 50 Compost

A.6.3 Seed Mixes

Nurse Crop Seed All Applications for Cool Weather Seeding Seed/Seed Grain Mixes Scientific Name Common Name Percentage (%) Germination Purpose Installation Window by Weight Percentage (%) Secale Cereale Cereal Rye 100.00 100 Cool-season nurse October to March crop to hold soils 1st Application Rate = 100 lbs./acre (1 lb. / 436 sf.)

172 Appendices 1 INTRODUCTION Seed Mix #1 Dry/Wet Conditions - Bottom and Sides 2

Wildflowers (Forbs) HYDROLOGY Scientific Name Common Name Percentage (%) Germination Purpose Installation by Weight Percentage Window (%) 3

Bouteloua gracilis Blue Grama 31.05 75 Soil Spring (March ROADWAY Stabilization - 1st - May 15th) or DRAINAGE DESIGN Warm-season Fall (Sept. 1st - crop Nov. 15th) if with Seed Mix #3 4 Bouteloua Buffalograss 11.00 94 - - BRIDGE dactyloides HYDRAULIC DESIGN Schizachyrium Little Bluestem 11.00 42 - - scoparium 5

Bouteloua Sideoats Grama 10.18 86 - - DESIGN curtipendula OPEN CHANNEL Andropogon Big Bluestem 4.95 - - - gerardii 6

Leptochloa dubia Green Sprangletop 4.95 - - - DRAINAGE STORAGE DESIGN Tripsacum Eastern Gamagrass 4.90 - - - dactyloides Sporobolus Sand Dropseed 4.90 - - -

cryptandrus 7 Elymus canadensis Prairie Wildrye 4.75 - - - CONTROL MEASURES EROSION & SEDIMENT Panicum virgatum Switchgrass 3.50 - - - Eragrostis trichodes Sand Lovegrass 3.02 - - - Sorghastrum Yellow Indiangrass 2.90 - - - nutans 8

Pascopyrum smithii Western 1.00 - - - FLOODPLAIN & SUMP Wheatgrass DESIGN REQUIREMENTS Bothriochloa Cane Bluestem 0.07 - - - barbinodis

Eriochloa sericea Texas Cupgrass 0.55 - - - 9

Hilaria belangeri Curly Mesquite 0.25 - - - REQUIREMENTS OTHER REGULATORY OTHER REGULATORY Tridens albenscens White Tridens 0.20 - - - Andropogon Bushy Bluestem or 0.20 - - - glomeratus or Halls Panicum 10 SUBMITTAL SUBMITTAL

Panicum hallii REQUIREMENTS Application Rate = 29 lbs./acre (1 lb. / 1,500 sf.) 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 173 APPENDICES Seed Mix #2 Dry/Wet Conditions - Bottom Wildflowers (Forbs) Scientific Name Common Name Percentage Germination Purpose Installation (%) Percentage Window by Weight (%) Centaurea americana American 49.66 8 Soil Stabilization - Fall (Sept. 1st - Basketflower Cool-season crop Nov. 15th) or Spring (March 1st - May 15th) if with Seed Mix #1 Desmanthus Illinois 23.91 12 - - illinoensis Bundleflower Dracopis amplexicaulis Clasping 8.07 99 - - Coneflower Coreopsis tinctoria Plains Coreopsis 3.23 - - - Rudbeckia hirta Black-Eyed Susan 3.23 - - - Salvia splendens Scarlet Sage 3.07 - - - Engelmannia Cutleaf Daisy 2.67 - - - peristenia Oenothera speciosa Pink Evening 1.94 - - - Primrose Helianthus Maximillian 0.96 - - - maximilliani Sunflower Solidago gigantea Giant Goldenrod 0.17 - - - Application Rate = 22 lbs./acre (1 lb. / 2,000 sf.)

174 Appendices 1 INTRODUCTION Seed Mix #3 Dry Conditions - Upper and Back Slopes 2

Wildflowers (Forbs) HYDROLOGY Scientific Name Common Name Percentage Germination Purpose Installation (%) Percentage Window by Weight (%) 3

Centaurea americana American 19.93 8 Soil Stabilization - Fall (Sept. 1st - ROADWAY Basketflower Cool-season crop Nov. 15th) or DRAINAGE DESIGN Spring (March 1st - May 15th) if with Seed 4

Mix #1 BRIDGE

Lupinus texensis Texas Bluebonnet 18.23 21 - - HYDRAULIC DESIGN Coreopsis tinctoria Plains Coreopsis 15.52 15 - -

Gaillardia pulchella Indian Blanket 15.32 88 - - 5 DESIGN

Monarda citriodora Lemon Mint 11.82 77 - - OPEN CHANNEL Dalea purpurea Purple Prairie 10.31 26 - - Clover 6

Dalea candida White Prairie Clover 6.66 91 - - DRAINAGE STORAGE DESIGN Chamaecrista Partridge Pea 1.90 - - - fasciculata Liatris punctata var. Gayfeather 0.20 - - -

mucronata 7 Solidago altissima Tall Goldenrod 0.10 - - - CONTROL MEASURES EROSION & SEDIMENT Lindheimera texana Texas Yellow Star 0.01 - - - Application Rate = 26 lbs./acre (1 lb. / 1,700 sf.) 8 FLOODPLAIN & SUMP DESIGN REQUIREMENTS 9 REQUIREMENTS OTHER REGULATORY OTHER REGULATORY 10 SUBMITTAL SUBMITTAL REQUIREMENTS 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 175 APPENDICES Seed Mix #4 - Overseed Wet and Moist Conditions - Regular Drainage or Seepage Along Bottom Grasses Scientific Name Common Name Percentage Germination Purpose Installation (%) Percentage Window by Weight (%) Secale cereale Cereal Rye Grain 75.39 98 Nurse crop to hold Nov. 1st - Feb. soils Andropogon gerardii Big Bluestem 8.20 98 Soil Stabilization - - Warm-season crop Tripsacum dactyloides Eastern Gamagrass - - - - Elymus canadensis Prairie Wildrye - - - - Leptochloa dubia Green Sprangletop - - - - Panicum virgatum Switchgrass - - - - Tridens albenscens White Tridens - - - - Andropogon virginicus Broomsedge - - - - Bluestem Andropogon Bushy Bluestem - - - - glomeratus Application Rate = 218 lbs./acre (1 lb. / 200 sf.)

Seed Mix #5 Access Roads or Pedestrian Access Ramps Grasses Scientific Name Common Name Percentage Germination Purpose Installation (%) Percentage Window by Weight (%) Bouteloua dactyloides Buffalograss 82.00 98 Soil Stabilization - Spring (March Warm-season crop 1st - May 15th); Fall (Sept. 1st - Nov. 15) if regular rain and up until 8 weeks before avg. frost date Bouteloua gracilis Blue Grama 17.00 98 - Hilaria belangeri Curly Mesquite 1.00 - - - Application Rate = 44 lbs./acre (3 lbs. / 1,000 sf. or 1 lb. / 333 sf.)

176 Appendices 1 INTRODUCTION Plant List #1 Recommended Plants for Rain Gardens and Bioretention 2 Trees Shrubs HYDROLOGY Scientific Name Common Name Scientific Name Common Name Cercis canadensis Eastern Redbud Baptisia australis False Indigo

Lagerstroemia indica Crapemyrtle Callicarpa americana American Beautyberry 3 ROADWAY ROADWAY Styphnolobium affine Eve’s Necklace Salvia greggii Autumn Sage DRAINAGE DESIGN Chilopsis linearis Desert Willow Hesperaloe parviflora Red Yucca Ilex vomitoria Yaupon Holly Rosmarinus officinalis Rosemary 4

Quercus sp. Oak Symphoricarpos Coralberry BRIDGE orbiculatus Acer truncatum Shantung Maple HYDRAULIC DESIGN Herbaceous Species Scientific Name Common Name 5 Eutrochium maculatum Joe Pye Weed DESIGN OPEN CHANNEL Lobelia cardinalis Cardinal Flower Rudbeckia hirta Black-Eyed Susan

Malvaviscus arboreaus var. Turk’s Cap 6 DRAINAGE

drummondii STORAGE DESIGN Symphyotrichum Aromatic Aster oblongifolium Salvia farinacea Mealy Blue Sage 7 Iris ser. Hexagonae Louisiana Iris CONTROL MEASURES Muhlenbergia capillaris Gulf Muhly EROSION & SEDIMENT Nassella tenuissima Mexican Feathergrass Muhlenbergia lindheimeri Lindheimer Muhly 8 FLOODPLAIN & SUMP DESIGN REQUIREMENTS 9 REQUIREMENTS OTHER REGULATORY OTHER REGULATORY 10 SUBMITTAL SUBMITTAL REQUIREMENTS 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 177 APPENDICES Plant List #2 Recommended Plants for Rain Gardens and Bioretention Trees Scientific Name Botanical Name Size (Height x Evergreen or Sun or Shade Location Spread) Deciduous (Wet or Dry) Cercis canadensis Eastern Redbud 20’-30’ x 20’- Deciduous Sun/Part Shade/ Dry 30’ Shade Cercis reniformis Redbud var. - 15’-20’ x 15’- Deciduous Sun/Part Shade Dry ‘Oklahoma’ ‘Oklahoma’, Texas or 20’ Mexican variety Lagerstroemia indica Crapemyrtle 28’-30’ x 30’- Deciduous Sun Dry 35’ Lagerstroemia indica Crapemyrtle 28’-30’ x 30’- Deciduous Sun Dry var. (“Indian” name var.) 35’ Chilopsis linearis Desert Willow 25’ x 25’ Deciduous Sun Dry Acer truncatum Shantung Maple 25’ x 20’ Deciduous Sun/Part Shade Semi-Wet/Dry Styphnolobium Eve’s Necklace 30’ x 20’ Deciduous Sun/Shade Semi-Wet/Dry affine Ilex decidua Possumhaw (away 15’-30’ x 15’- Deciduous Sun/Part Shade Wet/Dry from road edges) 20’ (with berries) Ilex vomitoria Yaupon Holly (Male 20’ x 20’ Evergreen Sun/Shade Wet/Dry by roadways) Ilex vomitoria Yaupon Holly 20’ x 20’ Evergreen Sun/Shade Wet/Dry (Female - other (with berries) areas) Quercus sp. Oak varieties 50’-60’ x 60’- Evergreen & Sun Wet/Dry 70’ Deciduous Ulmus crassifolia Cedar Elm 60’ x 30’ Deciduous Sun Wet/Dry

178 Appendices 1 INTRODUCTION Shrubs Scientific Name Common Name Size (Height x Evergreen or Sun or Shade Location Spread) Deciduous (Wet or Dry) 2 HYDROLOGY Symphorcarpos Indiancurrant 1’-6’ x 1’-2’ Deciduous Part Shade/ Dry orbiculatus Coralberry Shade Hesperaloe parviflora ‘Brakelight’ Red 2’ x 2’ Evergreen Sun/Part Shade Dry

‘Perpa’ ‘Brakelights’ Yucca 3 ROADWAY ROADWAY

Hesperaloe parviflora Red Yucca 3’ x 3’-5’ Evergreen Sun/Part Shade Dry DRAINAGE DESIGN (Hesperaloe) Hesperaloe parviflora Yellow Yucca 3’ x 3’-5’ Evergreen Sun/Part Shade Dry ‘Yellow’ (Hesperaloe) 4 Rosemary 4’-5’ x 4’-5’ Evergreen/ Sun Dry BRIDGE

Semi- HYDRAULIC DESIGN Evergreen Rosmarinus ‘Arp’ Rosemary 2’-3’ x 4’-5’ Evergreen/ Sun Dry 5

officinalis Arp Semi- DESIGN

Evergreen OPEN CHANNEL Salvia greggii Autumn Sage 2’-3’ x 4’-5’ Evergreen/ Sun Dry Semi- Evergreen 6

Amorpha fruticosa False Indigo Bush 8’-10’ x 10’-12’ Deciduous Part Shade/ Semi-Wet/ DRAINAGE Shade Semi-Dry/Dry STORAGE DESIGN Yucca pallida Pale-Leaf Yucca 1’-2’ x 1’-3’ Evergreen Sun Wet/Dry

Callicarpa americana American 4’-6’ x 5’-8’ Deciduous Part Shade/ Wet/Dry 7 Beautyberry Shade CONTROL MEASURES Sabal minor Dwarf Palmetto 4’ x 5’ Evergreen Shade Wet/Dry EROSION & SEDIMENT (Texas)

Ornamental Grasses 8 Scientific Name Common Name Size (Height x Winter Sun or Shade Location

Spread) Foliage (Wet or Dry) FLOODPLAIN & SUMP DESIGN REQUIREMENTS Benefit Nassella tenuissima Mexican Feathergrass 1’-2’ x 1’-2’ Yes Sun Dry

Muhlenbergia ‘Regal Mist’ Gulf 2’ x 3’ Yes Sun Wet/Dry 9 capillaris ‘Regal Muhly REQUIREMENTS

Mist’ OTHER REGULATORY Muhlenbergia Lindheimer Muhly 4’-5’ x 3’-4’ Yes & Semi- Sun/Part Shade Wet/Dry lindheimeri Evergreen Carex cherokeensis Cherokee Sedge 1’-2’ x 1’-2’ Evergreen Part Shade/ Wet/Dry 10 SUBMITTAL SUBMITTAL

Shade REQUIREMENTS Carex emoryi Emory’s Sedge 2’ x 2’ Semi- Sun/Part Shade Wet/Semi-Dry Evergreen

Chasmanthium Inland Sea Oats 3’-4’ x 2’ Yes Part Shade/ Wet/Semi-Dry 11 OPERATION & OPERATION latifolium Shade MAINTENANCE

Dallas Drainage Design Manual 179 APPENDICES Perennials Scientific Name Common Name Size (Height x Dieback or Sun or Shade Location Spread) Evergreen (Wet or Dry) Wedelia Zexmenia 1’-2’ x 2’-3’ Evergreen/ Sun/Part Shade Semi-Wet/Dry acapulcensis var. Semi- hispida Evergreen Symphyotricum Aromatic Aster 1’-3’ x 1’-2’ Winter Sun/Part Shade Semi-Wet/Dry oblongifolium Dieback Conoclinium greggii Gregg’s Mistflower 18”-2’ x 2’-3’ Winter Sun/Part Shade Semi-Wet/ Dieback Semi-Dry/Dry Salvia farinacea Mealy Blue Sage 2’-3’ x 2’-3’ Winter Sun Semi-Wet/ Dieback Semi-Dry/Dry Rudbeckia hirta Black-Eyed Susan 2’ x 2’ Winter Sun Wet/Dry Dieback Malvaviscus Turk’s Cap 2’-3’ x 3’-4’ Winter Part Shade/ Wet/Dry arboreaus var. Dieback Shade drummondii Symphyotricum Tall Aster 1’-3’ x 1’-2’ Winter Sun/Part Shade/ Wet/Semi- praealtum var. Dieback Shade Wet praealtum Eutrochium Joe Pye Weed 4’ x 2’ Winter Part Shade/ Wet/Semi- maculatum Dieback Shade Wet Lobelia cardinalis Cardinal Flower 2’ x 2’-4’ Winter Part Shade/ Wet/Semi- Dieback Shade Wet Iris ser. Hexagonae Louisiana Iris 3’ x 6” Winter Part Shade/ Wet/Semi- Dieback Shade Wet

A.6.4 Recommended Plants Constructed Wetlands

Plant List #3 - Deep Water Zone (6' to 18") Scientific Name Common Name Nuphar luteum Spatterdock, Cow Lily Mympheae mexicana Yellow Water Lily Mynphaea odorata Fragrant (White) Water Lily

180 Appendices 1

Stormwater Ponds and Constructed Wetlands INTRODUCTION

Plant List #4 - Aquatic Bench, Low Marsh, and High Marsh 2 (18" to NWL) HYDROLOGY Scientific Name Common Name Depth of Water - Planting Acrous calumus Sweetflag 3

Andropogon glomeratus Bushy Bluestem 0” ROADWAY DRAINAGE DESIGN Carex spp. Caric Sedges Eleocharis quadrangulata Squarestem Spikerush 0”-6”

Helianthus angustifolius Swamp Sunflower 4 BRIDGE Hibiscus laevis Halberdleaf Hibiscus HYDRAULIC DESIGN Hibiscus moscheutos Swamp Rosemallow 0” Hymenocallis liriosme Spring Spiderlily 0”-3” 5

Iris virginica Southern Blue Flag Iris 0”-3” DESIGN OPEN CHANNEL Juncus effuses Soft Rush, Common Rush 0”-3” Leersia oryzoides Rice Cut Grass

Panicum virgatum Switchgrass 0” 6 DRAINAGE

Peltandra virginica Arrow Arum, Smart Arum, Green Arum 0”-3” STORAGE DESIGN Polygonum hydropiperoides Smartweed Pontederia cordata Pickerelweed, Pickerel Rush 0”-6”

Pontederia lanceolata Pickerelweed, Pickerel Rush 0”-6” 7 Rudbeckia maxima Swamp Coneflower 0” CONTROL MEASURES EROSION & SEDIMENT Sagittaria lancifolia Lance-leaf Arrowhead, Bulltongue Arrowhead 0”-3” Sagittaria latifolia Duck Potato Sagittaria platyphyla Delta Arrowhead 0”-6”

Saururus cernuus Lizard’s Tail 0”-3” 8

Schoenoplectus americanus Three-square FLOODPLAIN & SUMP DESIGN REQUIREMENTS Schoenoplectus californicus Giant Bulrush, California Bulrush, Southern Bulrush Schoenoplectus tabernaemontani Softstem Bulrush Tradescantia ohioensis Spiderwort 0” 9 Woodwardia virginica Virginia Chain Fern REQUIREMENTS OTHER REGULATORY OTHER REGULATORY 10 SUBMITTAL SUBMITTAL REQUIREMENTS 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 181 APPENDICES Stormwater Ponds Constructed Wetlands

Plant List #5 - Wetland Plants Plant List #6 - Semi-Wet Zone (NWL to +6") (NWL to +4') Scientific Name Common Name Scientific Name Common Name Andropogon glomeratus Bushy Bluestem Andropogon glomeratus Bushy Bluestem Chasmanthium latifolium Upland Sea Oats Andropogon virginicus Broomsedge, Broom Grass Coreopsis tinctoria Dwarf Tickseed Chasmanthium latifolium Upland Sea Oats Euptorium serotinum Late Boneset Coreopsis tinctoria Dwarf Tickseed Helianthus maximiliani Maximilian Sunflower Elymus cadensis Canadian Wildrye Hibiscus laevis Halberdleaf Hibiscus Elymus virginicus Virginia Wildrye Liatris spicata Spiked Gayfeather Eupatorium fistolosum Joe Pye Weed Lobelia cardinalis Cardinal Flower Eupatorium serotinum Late Boneset Osmunda cinnamomea Cinnamon Fern Eustoma grandiflora Texas Bluebells Osmunda regalis Royal Fern Helianthus maximiliani Maximilian Sunflower Panicum capillare Witchgrass Hibiscus laevis Halberdleaf Hibiscus Pontederia cordata Pickerelweed, Pickerel Liatris spicata Spiked Gayfeather Rush Lobelia cardinalis Cardinal Flower Schoenoplectus Softstem Bulrush Malvaviscus drummondii Turk's Cap tabernaemontani Osmunda cinnamomea Cinnamon Fern Tripsacum dactyloides Eastern Gamagrass Osmunda regalis Royal Fern Panicum capillare Witchgrass Pontederia cordata Pickerelweed, Pickerel Rush Rudbeckia hirta Black-eyed Susan Schoenoplectus Softstem Bulrush tabernaemontani Sorgham nutans Yellow Indian Grass Tripsacum dactyloides Eastern Gamagrass

182 Appendices 1

Stormwater Ponds and Constructed Wetlands INTRODUCTION

Plant List #7 - Wooded Vegetation 2 (+6" and up) HYDROLOGY 6" to 4' - Regularly Inundated 4' and up - Periodically Inundated Herbaceous Species Herbaceous Species

Scientific Name Common Name Scientific Name Common Name 3 Andropogon virginicus Broomsedge, Broom Grass ROADWAY

Elymus canadensis Canadian Wildrye DRAINAGE DESIGN Elymus canadensis Canadian Wildrye Elymus virginicus Virginia Wildrye Elymus virginicus Virginia Wildrye Helianthus maximiliani Maximilian Sunflower

Eupatorium serotinum Late Boneset 4

Liatris pycnostachya Prairie Gayfeather BRIDGE

Eustoma grandiflora Texas Bluebells Malvaviscus drummondii Turk’s Cap HYDRAULIC DESIGN Helianthus maximiliani Maximilian Sunflower Panicum capillare Witchgrass Malvaviscus drummondii Turk’s Cap Tripsacum dactyloides Eastern Gamagrass 5 Panicum capillare Witchgrass Shrubs and Ornamental Trees DESIGN OPEN CHANNEL Rudbeckia hirta Black-eyed Susan Scientific Name Common Name Sorghastrum nutans Yellow Indian Grass Cornus drummondii Rough-Leaf Dogwood

Tripsacum dactyloides Eastern Gamagrass 6 Ilex decidua Possumhaw (Deciduous DRAINAGE

Shrubs and Ornamental Trees Holly) STORAGE DESIGN Scientific Name Common Name Lindera benzoin Spicebush Cephalanthus Common Buttonbush Myrica cerifera Southern Waxmyrtle occidentalis

Ptelea trifoliata Wafer Ash, Common 7 Ilex decidua Possumhaw (Deciduous Hoptree

Holly) CONTROL MEASURES Trees EROSION & SEDIMENT Myrica cerifera Southern Waxmyrtle Scientific Name Common Name Ptelea trifoliata Wafer Ash, Common Hoptree Taxodium distichum Bald Cypress

Trees Taxodium distichum var. Pond Cypress 8 nutans Scientific Name Common Name FLOODPLAIN & SUMP Fraxinus pennsylvanica Green Ash DESIGN REQUIREMENTS Taxodium distichum Bald Cypress Diospyros virginiana Common Persimmon Taxodium distichum var. Pond Cypress nutans Ulmus crassifolia Cedar Elm

Fraxinus pennsylvanica Green Ash Quercus lyrata Overcup Oak 9

Quercus nigra Water Oak REQUIREMENTS

Salix nigra Black Willow OTHER REGULATORY Quercus phellos Willow Oak Salix nigra Black Willow 10 SUBMITTAL SUBMITTAL REQUIREMENTS 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 183 APPENDICES Infrequently Inundated Herbaceous Species Trees Scientific Name Common Name Scientific Name Common Name Andropogon gerardii Big Bluestem Taxodium distichum Bald Cypress Asclepias tuberosa Butterfly-weed Fraxinus pennsylvanica Green Ash Bouteloua curtipendula Sideoats Grama Ulmus crassifolia Cedar Elm Bouteloua (Buchloe) Buffalograss Quercus lyrata Overcup Oak dactyloides Quercus nigra Water Oak Cynodon dactylon Bermuda Grass Quercus phellos Willow Oak Echinacea purpurea Purple Coneflower Quercus shumardii Shumard Oak Helianthus maximiliani Maximilian Sunflower Magnolia virginiana Sweetbay Magnolia Leptochola dubia Green Sprangletop Liatris puncata Dotted Gayfeather Liatris puncata var. Texas Gayfeather mucronatum Liatris pycnostachya Prairie Gayfeather Malvaviscus drummondii Turk’s Cap Panicum capillare Witchgrass Pennisetum Fountaingrass alopecuroides Poa arachnifera Texas Bluegrass Salvia farinacea Mealy Blue Sage Salvia greggii Autumn Sage Schizachyrium scoparium Little Bluestem Tripsacum dactyloides Eastern Gamagrass Valpia octoflora Common Sixweeksgrass Shrubs and Ornamental Trees Scientific Name Common Name Cornus drummondii Rough-Leaf Dogwood Ilex decidua Possumhaw (Deciduous Holly) Lindera benzoin Spicebush Myrica cerifera Southern Waxmyrtle Crataegus reverchonii Reverchon Hawthorn

184 Appendices 1 INTRODUCTION A.6.5 Operation and Maintenance Plan

Structural Components Corrective Action 2 HYDROLOGY –– Clogged inlets or outlets –– Remove sediment and debris from basins, drains, inlets, and pipes to maintain at least 50% conveyance capacity. –– Damaged liners and walls –– Replace broken downspouts, curb cuts, standpipes, and –– Cracked or exposed drain pipes screens as needed. Repair/seal cracks. 3 ROADWAY ROADWAY

–– Check dams –– Extend and secure liners above the high water mark to DRAINAGE DESIGN maintain water tight conditions. –– Clogged surface –– Vacuum or dry sweep permeable/porous pavers once a year. –– Cracked pipe, vault, or tank 4 BRIDGE –– Maintain rock check dams as per standard details. HYDRAULIC DESIGN –– Repair cracks with grout or City-approved materials or replace when cracks are 1 inch wide or more.

Vegetation 5 DESIGN

–– Dead or strained vegetation –– Replant per original planting plan, or substitute from OPEN CHANNEL Recommended Plant List. Maintain 90% cover in vegetated –– Tall or overgrown plants areas.

–– Weeds –– Irrigate as needed. Mulch as needed. Do not apply fertilizers, 6 DRAINAGE

herbicides, and pesticides. STORAGE DESIGN –– Large shrubs and trees –– Prune to allow foot traffic and to insure inlets and outlets can freely convey stormwater.

–– Manually remove weeds. Remove all plant debris. 7

–– Prevent large root systems from damaging subsurface CONTROL MEASURES EROSION & SEDIMENT structural components.

–– Mow natural grassed areas two times per year: July 1st and in dead of Winter (January 1st) to no shorter than 8 inches in height. Bag and remove from site all clippings and trimmings. 8 Growing / Filter Medium FLOODPLAIN & SUMP –– Erosion and/or exposed soils –– Fill and lightly compact areas of concern with soil mix DESIGN REQUIREMENTS from Materials Matrix. Stabilize soils with plantings from –– Scouring at inlets Recommended Plant List.

–– Ponding –– Replace splash pads at inlets with gravel/rock. 9 –– Slope slippage

–– Stabilize 3:1 slopes with plantings from Recommended Plant REQUIREMENTS List. OTHER REGULATORY –– Aggregate loss in pavers –– Remove the top 2-4 inches of sediment at inlets. Add soil mix from Materials Matrix to match elevation of inlet. Rake, till, or amend with soil mix to restore infiltration rate. 10 SUBMITTAL SUBMITTAL REQUIREMENTS –– Replace paver pore space with aggregate per original design. 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 185 APPENDICES A.6.6 Annual Maintenance Schedule Summer: Make any structural repairs. Improve filter medium as needed. Clear drains and inlets. Irrigate as needed.

Fall: Replant exposed soil and replace dead plants. Remove sediment and plant debris. Vacuum sweep pavers. Winter: Monitor infiltration/flow-through rates. Clear inlets A.7 and outlets/overflows to maintain conveyance.

Spring: Remove sediment and plant debris. Replant exposed soil and replace dead plants. Mulch as needed but do not FIGURES block the inlets, outlets, or flow paths with mulch.

All seasons: Weed as necessary. A.6.7 Maintenance Records All facility operators are required to keep an annual inspection and maintenance log. Record the date description, and contractor (if applicable) for all structural repairs, landscape maintenance, and facility cleanout activities. Keep work orders and invoices on file and make available upon request of the City inspector.

Access: Maintain ingress/egress to design standards.

Infiltration/Flow Control: All facilities shall drain within 24 hours. Record the time/date, weather, and site conditions when ponding occurs.

Pollution Prevention: All sites shall implement BMPs to prevent hazardous or solid wastes or excessive oil and sediment from contaminating stormwater. Record the time/date, weather, and site conditions if site activities contaminate stormwater. Record the time/date and description of the corrective action taken.

Vectors (Mosquitoes and Rodents): Stormwater facilities shall not harbor mosquito larvae or rats that pose a threat to public health or that undermine the facility structure. Monitor standing water for small wiggling sticks perpendicular to the water’s surface. Note holes/burrows in and around facilities. Record the time/date, weather, and site conditions when vector activity is observed

186 Appendices 1 INTRODUCTION A.7.1 Capacity of Triangular Gutters 2

EXAMPLE HYDROLOGY

NN SINS

Major Street, Type MB Enter Graph at .5’ 3

Pavement Width = 33” Intersect Cross Slope = 1/2” / 1’ ROADWAY Gutter Slope = 1.0% Intersect Gutter Slope = 1.0% DRAINAGE DESIGN Pavement Cross Slope = 1/2” / 1’ Read Gutter Capacity = 12 c.f.s. Depth of Gutter Flow = 0.5’

IND 4

Gutter Capacity BRIDGE HYDRAULIC DESIGN CAPACITY OF TRIANGULAR GUTTERS

GUTTER CAPACITY IN C.F.S. 0.5 1 2 3 4 5 10 20 30 40 100 5 DESIGN OPEN CHANNEL 6 1/8

3/16

1/4 DRAINAGE 3/8 1/2 STORAGE DESIGN

0.2 0.3 0.4 0.5 1.0 7 2.0 3.0 CONTROL MEASURES 5.0 EROSION & SEDIMENT

10.0

Cross Slope (in/ft)

Gutter Slope (ft/100ft) 8 FLOODPLAIN & SUMP DESIGN REQUIREMENTS 9 REQUIREMENTS

0.1 0.2 0.3 0.4 0.5 OTHER REGULATORY Depth of the gutter ﬂow (ft) 10 SUBMITTAL SUBMITTAL

Depth of REQUIREMENTS gutter ﬂow Cross Slope

(Roughness Coeffecient n = 0.0175) 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 187 APPENDICES A.7.2 Parabolic Crown Street Flow Capacity

10 9 8 7 6 5 4 3 2 1 0.9 0.8 0.7 0.6 0.5 0.4min SLOPE (ft/100ft) SLOPE SEE IDS CAPACI PAAIC ES

EAPE KNOWN F Collector Street, Type Pavement Width = 36’ Gutter Slope = 3.0% Gutter Difference = 0.2’ FIND Gutter Capacity of High Curb Gutter Capacity of Low Curb SOLUTION From 0.2’ on the high curb project horizontally to pivot line. From the pivot line draw a straight to gutter slope = 3.0% Read Q = 9.0 cfs for high curb From 0.2’ on the Low Curb Project Horizontally to pivot line. From the pivot line draw a straight to gutter slope = 3.0% Read Q = 17.0 cfs for low curb

/sec) (ft CAPACITY 3 8 6 5 4 3 2 1 50 40 30 20 10 0.8 0.6 0.5 0.4 0.3 0.2 0.1

LOW CURB PIVOT LINE PIVOT L0.2’ L0.4’ L0.6’ L0.8’ L1.0’ 36’ max H0.0’ H0.2’ H1.0’ H0.4’ H0.6’ H0.8’ (NON-COLLECTOR) L0.2’ L0.4’ L0.6’ L0.8’ L1.0’ 36’ max (COLLECTOR) H0.0’ H1.0’ H0.2’ H0.4’ H0.6’ H0.8’ STREET WIDTH L0.2’ L0.4’ L0.6’ 26’ HIGH CURB DIFFERENCE max H0.0’ H0.2’ H0.4’ H0.60’

188 Appendices 1 INTRODUCTION 2

10 9 8 7 6 5 4 3 2 1 0.9 0.8 0.7 0.6 0.5 0.4min HYDROLOGY SLOPE (ft/100ft) SLOPE 3 ROADWAY ROADWAY DRAINAGE DESIGN 4 BRIDGE HYDRAULIC DESIGN SEE IDS 5 DESIGN CAPACI PAAIC ES OPEN CHANNEL 6 DRAINAGE STORAGE DESIGN

EAPE KNOWN F Collector Street, Type Pavement Width = 44’ Gutter Slope = 2.0% Gutter Difference = 0.6’ FIND Gutter Capacity of High Curb Gutter Capacity of Low Curb SOLUTION From 0.6’ on the high curb project horizontally to pivot line. From the pivot line draw a straight to gutter slope = 2.0% Read Q = 3.0 cfs for high curb From 0.6’ on the Low Curb Project Horizontally to pivot line. From the pivot line draw a straight to gutter slope = 2.0% Read Q = 13.0 cfs for low curb

/sec)

CAPACITY (ft CAPACITY CONTROL MEASURES EROSION & SEDIMENT 3 8 6 5 4 3 2 1 50 40 30 20 10 0.3 0.2 0.1 0.8 0.6 0.5 0.4 LOW CURB 8

FLOODPLAIN & SUMP

DESIGN REQUIREMENTS PIVOT LINE PIVOT 9 REQUIREMENTS OTHER REGULATORY OTHER REGULATORY L0.2’ L0.4’ L0.6’ L0.8’ L1.0’ 48’ max H1.0’ H0.6’ H0.8’ H0.0’ H0.2’ H0.4’ 10 SUBMITTAL SUBMITTAL REQUIREMENTS STREET WIDTH L0.2’ L0.4’ L0.6’ L0.8’ L1.0’ 44’ max H0.6’ H0.8’ H1.0’ H0.0’ H0.2’ H0.4’ 11 OPERATION & OPERATION MAINTENANCE HIGH CURB DIFFERENCE

Dallas Drainage Design Manual 189 APPENDICES A.7.3 Alley Conveyance Without Curb EAPES

A AE I CS

PROPERTY LINE 15’

10’

1.5” 3” 6”

IEN EIED

Concrete n = .0175 (1) Concrete Alley Conveyance Grass n = .035 K = 1.486 AR2/3 Alley width = 10’ n D = Alley depression = 3” = 0.25’ Alley easment width = 15’ (2) Alley Easement Conveyance 1/2 D = Alley depression = 4.5” = 0.375’ (3) Gutter Flow Q = KSy

Gutter slope = Sy (check your proﬁle; assume (assuming Sy = 2.2%) normal ﬂow conditions)

SINS A = (10’ * 0.25’) + 1.25 ft2 2 2 2 1/2 (1) Concrete Alley Conveyance P = 2 [(0.25) + (5) ] + 2(0.5) = 10.012ft D = 0.25’ R = A = 1.25ft2 = 0.125ft n = 0.0175 P 10.012ft K = 1.486AR2/3 = 26.51ft3 n 1/2 1/2 Q = KSy = (26.51) (0.022) = 3.93 cfs

(2) Alley Easment Conveyance A = 15’ * 0.375’ + 2.813 ft2 D = 0.375’ 2 n = 0.0233 P = 2 [(0.375)2 + (7.5)2 ]1/2 = 15.019ft

R = A = 0.187ft P Weighted (perimeter) “n” value: n = (10.012’) (0.0175) + (5.006’) (0.035) = 0.0233 15.018’ K = 1.486AR2/3 = 58.71ft3 n

1/2 1/2 Q = KSy = (58.71) (0.022) = 8.71 cfs

190 Appendices 1 INTRODUCTION A.7.4 Alley Conveyance With Curb 2 HYDROLOGY

AE I C 3 ROADWAY ROADWAY

PROPERTY LINE 15’ DRAINAGE DESIGN

10’ 4

6” BRIDGE 3” HYDRAULIC DESIGN 6” 5 DESIGN

CNCEE AE CNEANCE A = (10’ * 0.25’) + (10’ * 0.5’) = 6.25 ft2 OPEN CHANNEL 2

2 2 1/2

P = 2 [(0.25) + (5) ] + 2(0.5) = 11.012ft 6 DRAINAGE STORAGE DESIGN R = A = 6.25ft2 = 0.568ft P 11.012ft

K = 1.486AR2/3 = 363.8ft3 7 n CONTROL MEASURES EROSION & SEDIMENT

1/2 1/2 Q = KSy = (368.8) (0.022) = 53.96 cfs 8 FLOODPLAIN & SUMP DESIGN REQUIREMENTS 9 REQUIREMENTS OTHER REGULATORY OTHER REGULATORY 10 SUBMITTAL SUBMITTAL REQUIREMENTS 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 191 APPENDICES A.7.5 Curves for Determining the Critical Depth in Open Channels z = 0.5 z = 1.0 z = 1.5 z = 2.0 z = 2.5 z = 3.0 z = 4.0 100 100 10 10 O

z = 0 (RECTANGULAR) 0 = z CIRCULAR y 1 1 (CIRCULAR SECTIONS) (TRAPEZOIDAL SECTIONS) 2.5 2.5 O 0.1 0.1 VALUES OF z/d VALUES VALUES OF z/b VALUES y b z 1 0.01 0.01 0.001 0.001 8 6 4 2 1

0.8 0.6 0.4 0.2 0.1

O 0.08 0.06 0.04 0.02 0.01 VALUES OF y/b and y/d and y/b OF VALUES

192 Appendices 1 INTRODUCTION A.7.6 Section 2 Figures

Figure 2.1 Shallow Concentrated Flow Average Velocity 2 50 HYDROLOGY 3 ROADWAY ROADWAY DRAINAGE DESIGN 4 20 BRIDGE HYDRAULIC DESIGN 5 DESIGN OPEN CHANNEL

10 6 DRAINAGE STORAGE DESIGN

06 7 CONTROL MEASURES 04 EROSION & SEDIMENT S

npaved

Paved 8 FLOODPLAIN & SUMP DESIGN REQUIREMENTS 005 9 REQUIREMENTS OTHER REGULATORY OTHER REGULATORY

005 10 SUBMITTAL SUBMITTAL REQUIREMENTS 11 005 OPERATION & OPERATION 1 2 4 6 10 20 MAINTENANCE A

Dallas Drainage Design Manual 193 APPENDICES Figure 2.2 Areal Reduction Factors for Small Watersheds for 50% AEP or Greater 1-day Design Storms

D D S A

A C

194 Appendices 1 INTRODUCTION A.7.7 Section 3 Figures 2 HYDROLOGY Figure 3.2 Parabolic Crown Street Flow Capacity 3

ROADWAY DRAINAGE DESIGN

4 BRIDGE HYDRAULIC DESIGN

5 DESIGN OPEN CHANNEL

6 DRAINAGE STORAGE DESIGN

7 CONTROL MEASURES EROSION & SEDIMENT

ee id 8

ee id S S FLOODPLAIN & SUMP DESIGN REQUIREMENTS

ee id

9 REQUIREMENTS OTHER REGULATORY 10 SUBMITTAL SUBMITTAL REQUIREMENTS C CS 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 195 APPENDICES Figure 3.10 Curb Inlets on Grade: Ratio of Intercepted to Total Flow

I I

196 Appendices 1

Figure 3.11 Y-Inlet Capacity Curves at Sag Point INTRODUCTION 2 HYDROLOGY

3 ROADWAY ROADWAY

DRAINAGE DESIGN 4 BRIDGE HYDRAULIC DESIGN

DESIGN

OPEN CHANNEL 6 I

DRAINAGE STORAGE DESIGN

7 CONTROL MEASURES EROSION & SEDIMENT 8

FLOODPLAIN & SUMP DESIGN REQUIREMENTS CS 9 REQUIREMENTS OTHER REGULATORY OTHER REGULATORY 10 SUBMITTAL SUBMITTAL REQUIREMENTS 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 197 APPENDICES Figure 3.17 Head Losses in Laterals, Wyes, and Enlargements Head Losses & Gains for Laterals

ne ine sd e es e p ine ine A A in Head Losses & Gains for Laterals ne ine sd e es e p ine A A A A ine in e nd pipe A A in 90˚ Lateral Manhole on Main Line A A A A in e nd pipe Figure 3.18 Head Losses for Junction Boxes, Manholes, and Bends ies Note 90˚ Lateral Mitered Bends 60˚ Lateral Manhole on Main Line Plan Note ed ss ppied einnin end ends e sed n i e

45˚ Lateral ies peissin e dine eninee Note ˚ Bend ˚ Bend Mitered Bends 60˚ Lateral Plan Note

ed˚ Bend ss ppied einnin˚ Bend Section end ends e sed n i e 45˚ Lateral peissin e dine eninee ˚ Bend ˚ Bend

˚ Bend ˚ Bend Section

198 Appendices 1

Figure 3.25 Over-Embankment Flow Adjustment Factor INTRODUCTION 2 HYDROLOGY 3 ROADWAY ROADWAY DRAINAGE DESIGN 4 BRIDGE HYDRAULIC DESIGN 5 DESIGN

OPEN CHANNEL 6 DRAINAGE STORAGE DESIGN 7 CONTROL MEASURES EROSION & SEDIMENT 8

FLOODPLAIN & SUMP DESIGN REQUIREMENTS

9 REQUIREMENTS OTHER REGULATORY OTHER REGULATORY 10 SUBMITTAL SUBMITTAL REQUIREMENTS 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 199 APPENDICES Figure 3.32 Design of Riprap Apron under Minimum Tailwater Conditions

e ipe 3D iee O d=36 d=42 d=48 d=54 d=60 d=66 d=72 d=78 d=84 d=90 d=96 W = DO + 0.4La (DO ) La ie 0.50o

d=30 a

d=24 d=27

d=21

d=18 A L d=15 d=12

v=30

v=25 S 50

v=20 d v=15 v=10 d=12 d=15 d=78d=84d=90d=96 d=18 d=21d=24d=27d=30 d=36 d=42 d=48d=54d=60d=66d=72 D es e ped

200 Appendices 1

Figure 3.33 Design of Riprap Apron under Maximum Tailwater Conditions INTRODUCTION 2 3D

e ipe O HYDROLOGY

iee W = DO + 0.4La

(DO ) 3 La ROADWAY ie > 0.50 DRAINAGE DESIGN o a

4 A L BRIDGE HYDRAULIC DESIGN

d=96 d=90 d=84 d=78 d=72 v=40 5 d=66 DESIGN d=60 d=54 OPEN CHANNEL d=48 v=35 d=42 d=36 d=30 d=12 d=24d=27 d=15 d=18 d=21 6 v=30 DRAINAGE STORAGE DESIGN S 50 d

v=25 d=96 d=90

d=78d=84 7 v=20 d=72 v=15 d=66 d=54d=60 CONTROL MEASURES v=10 d=48 EROSION & SEDIMENT d=36 d=42 v=5 d=30 d=12 d=15 d=18 d=21d=24d=27 D es e ped 8 FLOODPLAIN & SUMP DESIGN REQUIREMENTS 9 REQUIREMENTS OTHER REGULATORY OTHER REGULATORY 10 SUBMITTAL SUBMITTAL REQUIREMENTS 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 201 APPENDICES Figure 3.34 Dimensionless Rating Curves for the Outlets of Rectangular Culverts on Horizontal and Mild Slopes

Q/D 2.5 = 5.5

VO D

YO TW

Q/D 2.5 = 0.0 in ep YO D iee e TW ie ep

TW/D

202 Appendices 1

Figure 3.35 Dimensionless Rating Curves for the Outlets of Circular Culverts on Horizontal and Mild Slopes INTRODUCTION

HYDROLOGY 3 ROADWAY ROADWAY

DRAINAGE DESIGN 4 Q/BD 3/2 = 5.0 BRIDGE HYDRAULIC DESIGN

5 DESIGN OPEN CHANNEL

DRAINAGE STORAGE DESIGN VO D

7 CONTROL MEASURES EROSION & SEDIMENT

D VO TW 8 FLOODPLAIN & SUMP DESIGN REQUIREMENTS D

B 9

REQUIREMENTS in ep OTHER REGULATORY YO 3/2 D ei e Q/BD = 0.0 B id e Q isce 10 SUBMITTAL SUBMITTAL

TW ie ep REQUIREMENTS

11 OPERATION & OPERATION TW/D MAINTENANCE

Dallas Drainage Design Manual 203 APPENDICES Figure 3.36 Relative Depth of Scour Hole Versus Froude Number at Brink of Culvert with Relative Size of Riprap as a Third Variable

e in

esin isce e edin ie c ei d Ae in e nded c An c

ien in ep A necn ecins e in ep e ecin ℄

e e Note: 2 ≤ s ≤ 4 d e e d i d

d e ipp e eied n d ns nne d e nse sin d

D S

204 Appendices

EAIE DEP SC E ESS DE NE A IN CE I EAIE SIE IPAP AS A ID AIAE 1 INTRODUCTION A.7.8 Section 5 Figures 2

Figure 5.1 Hydraulic Jump HYDROLOGY ne ss in p

ne nein p ne nein p 3

de e ROADWAY D (Height of Jump) DRAINAGE DESIGN c iic ep een eps Aene eps

4 BRIDGE HYDRAULIC DESIGN

5 DESIGN

A OPEN CHANNEL

E 6

S E DRAINAGE D STORAGE DESIGN

Figure 5.2 Hydraulic Jump Conjugate Depth – Horizontal, Rectangular Channel 7

CONTROL MEASURES EROSION & SEDIMENT

8 FLOODPLAIN & SUMP DESIGN REQUIREMENTS

9 REQUIREMENTS OTHER REGULATORY OTHER REGULATORY

10 SUBMITTAL SUBMITTAL REQUIREMENTS

11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 205 APPENDICES

Figure 5.3 Length of Jump for a Rectangular Channel

206 Appendices 1 INTRODUCTION 2 HYDROLOGY 3 ROADWAY ROADWAY DRAINAGE DESIGN 4 BRIDGE HYDRAULIC DESIGN 5 DESIGN OPEN CHANNEL 6 DRAINAGE STORAGE DESIGN 7 CONTROL MEASURES EROSION & SEDIMENT 8 FLOODPLAIN & SUMP DESIGN REQUIREMENTS 9 REQUIREMENTS OTHER REGULATORY OTHER REGULATORY 10 SUBMITTAL SUBMITTAL REQUIREMENTS 11 OPERATION & OPERATION MAINTENANCE

Dallas Drainage Design Manual 207 APPENDICES