West Branch Susquehanna Watershed Act 167 Stormwater Management Plan June 2004 Prepared by Union County in conjunction with Union County Courthouse The preparation of the West Branch Susquehanna Stormwater Management Plan has been funded in part by a grant from the Pennsylvania Department of Environmental Protection Bureau of Watershed Conservation. WEST BRANCH SUSQUEHANNA RIVER WATERSHED ACT 167 STORMWATER MANAGEMENT PLAN JUNE 2004 X:\21\2189\2189008\Reports\plan\West Branch_FINAL.doc Table of Contents: Section 1 – Introduction 1 1.0 Introduction 1 1.1 Stormwater Runoff – Its Problems and Its Solutions 1 Section 2 – Act 167 Watershed Level Stormwater Management Planning & Implementation 2 2.0 The Pennsylvania Stormwater Management Act, Act 167 2 2.1 Plan Preparation Strategy 3 Stage A - Data Collection and Analysis 4 Stage B - Technical Analysis 5 Stage C – Public/Municipal Participation 6 Stage D - Plan Preparation and Implementation 8 Section 3 – West Branch Susquehanna River Watershed Characteristics 9 3.0 General Description 9 3.1 Political Features 10 3.2 Natural Features 10 3.3 Hydrology 12 3.4 Existing Stormwater Drainage Problem Areas 12 3.5 Suggested Solutions 13 3.6 Problem Area Remediation approach 13 3.7 Significant Obstructions 14 3.8 Designation of Stormwater Hotspots 19 Section 4 – Watershed Technical Analysis – Modeling 21 4.0 Hydrologic Model 21 4.1 Modeling Results & Release Rates 22 Section 5 – Technical Standards and Criteria for Control of Stormwater Runoff 24 5.0 Introduction 24 5.1 Water Quality Volume (WQv) 24 5.2 Recharge Volume Requirements (Rev) 27 5.3 Channel Protection Storage Volume Requirements (Cpv) 29 5.4 Overbank and Extreme Event Flood Protection Requirements (Release Rates) 33 5.5 Design Example: Computing Stormwater Storage Volumes 34 Section 6 – Runoff Control Techniques and Their Efficiencies 39 6.0 Acceptable Urban Best Management Practices (BMP) Options 39 Section 7 – Municipal Handbook 41 7.0 Introduction - Why Stormwater Matters 41 7.1 Declining Water Quality 42 7.2 Intent of the Act 167 Plan 42 7.3 Suggested Best Management Practices 42 7.4 BMP Maintenance 43 7.4.1 Overview of BMP Maintenance 44 7.4.2 Routine Maintenance Needs 45 7.4.3 Nonroutine Maintenance 46 7.4.4 Maintenance Responsibilities 48 7.4.5 Estimating Routine Costs 49 7.4.6 Estimating Nonroutine Costs 49 7.4.7 Planning Ahead 49 7.4.8 Access for Maintenance 49 7.4.9 Maintenance Agreements 50 7.5 Effective Site Planning 50 7.5.1 Some Important Principles of Effective Site Planning 50 (i) 7.5.2 Resources for Identifying and Mapping Sensitive Areas 51 7.5.3 Important Functions of Sensitive Areas and How They are Best Protected 52 7.5.4 Preserving Natural Hydrologic Conditions 53 7.5.5 Reducing or Disconnecting Impervious Surface Areas 54 7.5.6 Preserving Natural Drainage Features 55 7.5.7 Protecting Natural Depression Storage Areas 55 7.6 Site Planning and Land-Use Techniques to Minimize Efforts of Development 55 7.6.1 Setbacks and Buffers 56 7.6.2 Cluster Development 57 7.6.3 Zoning Restrictions 58 7.6.4 Conservation Easements 58 7.6.5 Development Designed to Fit Site Topography 58 Section 8 – Plan Review Adoption and Updating Procedures 59 8.0 Plan Review and Adoption 59 8.1 Procedure for Updating the Plan 60 Section 9 – Priorities for Implementation of Technical Standards and Criteria 62 9.0 Summary of Plan Conclusions and Recommendations 62 Section 10 - Model Act 167 Stormwater Management Ordinance 63 Tables: Table 2.0 - Existing Municipal Ordinance Matrix, West Branch Susquehanna River Watershed ............... 4 Table 2.1 - West Branch Susquehanna River Watershed Plan Advisory Committee (WPAC) .................... 6 Table 2.2 - West Branch Susquehanna River Watershed Municipal Engineer’s Committee (MEC) ........... 7 Table 2.3 - West Branch Susquehanna River Watershed Legal Advisory Committee (LAC) ..................... 7 Table 3.0 - Municipalities Lying Within The Watershed ........................................................................... 10 Table 3.1 - Summary of Obstructions ......................................................................................................... 14 Table 3.2 - Classification of Stormwater Hotspots ..................................................................................... 20 Table 4.0 - Comparison of HEC-HMS and FEMA Peak Flows at Dog Run .............................................. 22 Table 4.1 - Summary of Release Rates ....................................................................................................... 23 Table 5.0 - Summary of the Watershed-Wide Stormwater Criteria ............................................................ 24 Table 7.0 - Summary of BMP Descriptions ................................................................................................ 43 Table 7.1 - Components of a Maintenance Program................................................................................... 44 Table 7.2 - Inspection Checklist ................................................................................................................. 46 Figures: Figure 5.0 - Relationship Between Impervious Cover and Water Quality Volume ................................... 25 Figure 5.1 - Relationship Between Rev and Site Impervious Cover ........................................................... 28 Figure 5.2 - Example of Conventional Stormwater Detention Pond .......................................................... 31 Figure 5.3 - Design Example: The Meadows ............................................................................................ 35 Figure 7.0 - Water Balance at a Developed and Undeveloped Site ............................................................ 41 (ii) Plates: 1. West Branch Watershed 2. Hydrologic Soils 3. Stormwater Problem Areas 4. West Branch Subwatersheds 5. Significant Obstructions 5a. Significant Obstructions 6. Existing Land Use 7. Future Land Use 8. Limestone Areas 9. Flood Zones & Wetlands 9a. Flood Zones & Wetlands with Addressable Structures Appendices: A Review of Related Documents B Review of Relevant Municipal Ordinances and Flood Insurance Studies C Union County Rainfall Data D Stormwater Credits for Effective Site Planning E Computation of Peak Discharge for Water Quality Storm F Charts for Computation of Channel Protection Storage Volume G Watershed Data and Release Rate Computations (iii) KEY SYMBOLS AND ACRONYMS USED IN THE PLAN A – Drainage Area Ao – Orifice Area BMP – Best Management Practice cfs – Cubic Feet per Second CN – Curve Number Cpv – Channel Protection Storage Volume DEP – Pennsylvania Department of Environmental Protection do – Orifice Diameter ED – 24-Hour Drawdown of the Water Quality Volume EPA – Environmental Protection Agency FIA – Federal Insurance Administration FEMA – Federal Emergency Management Agency GIS – Geographic Information System HEC-HMS – Hydrologic Engineering Center Hydrologic Modeling System HSG – Hydrologic Soil Group I – Percent Impervious Cover Ia – Initial Abstraction LAC – Legal Advisory Committee MEC – Municipal Engineer’s Committee NPDES – National Pollutant Discharge Elimination System NRCS – Natural Resource Conservation Service (previously SCS) NWI – National Wetlands Inventory P – Precipitation Depth PENNDOT – Pennsylvania Department of Transportation PSP – Project Study Plan PUD – Planned Unit Development Qa – Post Development Runoff Depth qi – Peak Inflow Discharge qo – Peak Outflow Discharge qu – Unit Peak Discharge Rev – Recharge Volume Rv – Volumetric Runoff Coefficient S – Soil Specific Recharge Factor SCS – Soil Conservation Service T – Lag Time tc – Time of Concentration TDR – Transfer of Development Rights TR-20 – Technical Release No. 20 Project Formulation-Hydrology, Computer Program TR-55 – Technical Release No. 55 Urban Unit Hydrology for Small Watersheds UCPC – Union County Planning Commission USDA – United States Department of Agriculture USGS – United States Geological Survey Vr – Volume of Runoff Vs – Volume of Storage Vt – Total Volume Vv – Volume of Voids WPAC – Watershed Plan Advisory Committee WQv – Water Quality Storage Volume (iv) WEST BRANCH SUSQUEHANNA RIVER WATERSHED ACT 167 STORMWATER MANAGEMENT PLAN Section 1 – Introduction 1.0 Introduction This plan has been created for the West Branch Susquehanna River Watershed in Union County, Pennsylvania, and is intended to comply with the Pennsylvania Stormwater Management Act, Act 167, of 1978. The West Branch Susquehanna River Watershed is located in eastern Union County. The watershed consists of approximately 38-square miles, which is subdivided into five areas, bisected by White Deer Hole Creek, White Deer Creek, Buffalo Creek, and Bull Run. The watershed drains from the west, eastward until its confluence with the West Branch of the Susquehanna River. The focus of this plan is to create and implement a watershed-wide set of standards and criteria to manage stormwater runoff. 1.1 Stormwater Runoff – Its Problems and Its Solutions The water that runs off the land into surface waters during and immediately following a rainfall event is referred to as stormwater. In a watershed undergoing urban expansion, the volume of stormwater resulting from a particular rainfall event increases because of the reduction in pervious land area (i.e., natural land being covered by pavement, concrete, or buildings). That is, the alteration of natural land cover and land contours to residential, commercial, industrial, and even agricultural uses results in decreased infiltration of rainfall