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Drainage Design Manual Waterway Management Plan VOLUME III Drainage Design Manual City of San Luis Obispo County of San Luis Obispo Department of Public Works Flood Control District - Zone 9 955 Morro Street 1050 Monterey Street, Room 207 San Luis Obispo, California 93401 San Luis Obispo, California 93408 San Luis Obispo Creek Waterway Management Plan VOLUME III Drainage Design Manual City of San Luis Obispo Department of Public Works 955 Morro Street San Luis Obispo, California 93401 and County of San Luis Obispo Flood Control District - Zone 9 1050 Monterey Street, Room 207 San Luis Obispo, California 93408 February 2003 TABLE OF CONTENTS USER’S GUIDE ...........................................................................................................i FOREWORD .......................................................................................................... 1 SECTION 1.0 DRAINAGE MANUAL OBJECTIVES....................................... 2 SECTION 2.0 PROJECTS REQUIRING HYDROLOGY/HYDRAULICS AND DRAINAGE FACILITY DESIGN REVIEW ........................................................ 3 2.1 Drainage Master Plan..................................................................................... 3 2.2 Drainage Design Review............................................................................... 4 2.3 Submittal Requirements................................................................................. 5 2.3.1 Hydrologic and Hydraulic Analysis Report............................................. 5 SECTION 3.0 CORE REQUIREMENTS AND RESTRICTIONS FOR PLANNING & DESIGN ........................................................................................ 9 3.1 Discharge At Natural Locations..................................................................... 9 3.2 On-Site Conveyance Design........................................................................ 10 3.3 Off-Site Facility Analysis, Design, and Mitigation (No Adverse Impact Part A Policy)............................................................. 10 3.4 Channel Impact Assessment, Design, and Mitigation (No Adverse Impact Part B Policy) ............................................................. 11 3.5 Floodplain Management .............................................................................. 12 3.5.1 In-fill Floodplain Regulations................................................................ 12 3.5.2 Mid-Higuera Specific Plan Area............................................................ 13 3.5.3 Special Floodplain Management Zone Regulations .............................. 14 3.6 Bank Stabilization Guidelines...................................................................... 16 3.6.1 General Intent of Bank Stabilization Guidelines and Design Requirements ......................................................................................... 16 3.6.2 Design Approach ................................................................................... 17 3.6.3 Design Review....................................................................................... 17 3.6.4 Preference for Vegetative and Biotechnical Approaches to Bank Stabilization ........................................................................................... 18 3.6.5 Limitations On Use of Structural Approaches to Bank Stabilization.... 18 3.6.6 Retrofitting and Repair or Replacement of Existing Hydraulic Structures and Revetments...................................................................................... 18 3.7 Erosion Control and Stormwater Quality Management............................... 19 3.7.1 Erosion and Stormwater Quality Impacts-Prohibited............................ 19 3.7.2 Erosion control Planning Requirements ................................................ 20 3.8 Channel Maintenance and Management...................................................... 21 SLO Creek Drainage Design Manual February 2003 SECTION 4.0 HYDROLOGIC & HYDRAULIC ANALYSIS......................... 22 4.1 Hydrologic Analysis .................................................................................... 22 4.1.1 General................................................................................................... 22 4.1.2 Use of Rational Method for Drainage Facility Design for Catchments Under 40 Hectares (100 Acres).............................................................. 22 4.1.3 General Procedure for the Rational Method .......................................... 28 4.1.4 Example Problem................................................................................... 31 4.1.5 Use of SLO/Zone 9 hydrology Model for Catchment Areas Greater than 40 Hectares (100 acres).......................................................................... 34 4.1.6 Hydrology Report .................................................................................. 35 4.2 Open Channel Hydraulic Analysis............................................................... 35 4.2.1 General................................................................................................... 35 4.2.2 Hydraulic Analysis of Projects on Major and Secondary Waterways... 36 4.2.3 Hydraulic Analysis of Major and Secondary Waterways Not Covered by an Existing HEC-RAS Hydraulic Model............................................... 36 4.2.4 Hydraulic Analysis of Minor Waterways and Closed Conduits............ 37 4.2.5 Special Circumstances........................................................................... 37 4.2.6 Submittal Requirements......................................................................... 37 SECTION 5.0 ANALYSIS AND DESIGN REQUIREMENTS........................ 38 5.1 Channel Classification and Definitions ....................................................... 38 5.2 Channel Design Flow Requirements ........................................................... 41 5.3 Open Channel Design Criterial for Major and Secondary Waterways........ 42 5.3.1 Constructed Natural Channel Design..................................................... 42 5.3.1.1 Cross - Section Design........................................................................... 43 5.3.1.2 Low-Flow Channel ................................................................................ 44 5.3.1.3 In-Channel Bench or Floodplain Terrace .............................................. 44 5.3.1.4 Bank Slope............................................................................................. 45 5.3.1.5 Channel Planform.................................................................................. 45 5.3.2 By-Pass Channels................................................................................... 45 5.3.3 Modified Channels................................................................................. 46 SECTION 6.0 ANALYSIS & DESIGN OF BANK STABILIZATION STRUCTURES..................................................................................................... 50 6.1 General......................................................................................................... 50 6.2 Design Goals and Design Requirements...................................................... 50 6.3 Design References ....................................................................................... 52 6.4 Project Permitting & Approval Process....................................................... 53 6.5 Design Steps................................................................................................. 53 6.5.1 Overview of Design Steps ..................................................................... 54 6.5.2 Detailed Design Procedures................................................................... 55 6.6 Acceptable Bank Stabilization Structures.................................................... 70 6.6.1 Vegetative and Biotechnical Approaches .............................................. 70 6.6.2 Structural and Integrated Approaches.................................................... 72 6.7 Procedures for Designing Rock Slope Protection........................................ 77 6.7.1 Collect River/Stream Data ..................................................................... 77 6.7.2 Inspect Site............................................................................................. 77 SLO Creek Drainage Design Manual February 2003 6.7.3 Determine Minimum Stone Weight....................................................... 78 6.7.4 Determine RSP-Class of Outside Layer ................................................ 78 6.7.5 Determine the Required Layers of RSP................................................. 81 6.7.6 Determine the Thickness of the RSP Revetment................................... 83 6.7.7 Review Hydraulic Calculations at Site With RSP and Possibility of Vegetation.............................................................................................. 84 SECTION 7.0 DESIGN OF CONDUITS, CULVERTS, AND MODIFIED OPEN CHANNELS ON MINOR WATERWAYS.............................................. 85 7.1 Extension of Public Storm Drainage Systems ............................................. 86 7.2 Design .......................................................................................................... 86 7.2.1 Channel and Conduit Capacity .............................................................. 86 7.2.2 Channel Alignment and Chanel Stability .............................................. 86 7.2.3 Storm Drain Location and Alignment...................................................
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