LITTLE LEHIGH CREEK WATERSHED - ACT 167 - STORM WATER MANAGEMENT PLAN UPDATE This is the text prepared by the Lehigh Valley Planning Commission on behalf of Lehigh County and Berks County. It contains revisions, as necessary, based on comments received from the Little Lehigh Creek Watershed Advisory Committee, the Little Lehigh Municipal Engineers Committee, the Little Lehigh Lawyers Advisory Committee, the affected municipalities, the general public, the Berks County Planning Commission and the Lehigh County Board of Commissioners. The preparation of this report was financed through the Pennsylvania Storm Water Management Grant Assistance Program administered by the Department of Environmental Protection. This grant program provides for seventy-five percent (75%) State funding with twenty-five (25%) local match provided by Lehigh County. Final Plan June 1999 Adopted by Lehigh County September 1999 Adopted by Berks County November 1999 Approved by DEP June 2000 LEHIGH VALLEY PLANNING COMMISSION Earl B. Lynn, Chair Geraldine Szakmeister, Vice Chair Eleanore M. Hayden, Treasurer Lucy H. Ackerman Robert E. Korp Jane S. Baker James F. Lancsek Arthur F. Barwick Terry J. Lee Sandra Reed Bentley Henry A. Lubsen, Jr. Anthony J. Boyle Stanley M. Lysek J. William Brooks Grayson E. McNair Donald Cunningham Robert O’Neil Percy H. Dougherty Philip A. O’Reilly Timothy J. Edinger Glenn F. Reibman Ira J. Faro Dale M. Rex Charles L. Fraust Joan Rosenthal Steven L. Glickman Rodney K. Schlauch Thomas Goldsmith J. Michael Schweder Thomas Gorr Gerald E. Seyfried Samuel A. Guttman Glenn D. Solt Michael C. Hefele Todd A. Stephens William L. Heydt Richard R. Yost Nils Hovik LEHIGH VALLEY PLANNING COMMISSION STAFF Michael N. Kaiser, AICP Executive Director Frederic H. Brock, AICP Assistant Director ** Geoffrey A. Reese, P.E. Chief Engineer Olev Taremäe, AICP Chief Planner Joseph L. Gurinko, AICP Chief Planner Howard L. Kutzler, AICP Senior Community Planner ** Laura M. Eberly, P.E. Senior Engineer * Thomas K. Edinger Senior GIS Analyst Susan L. Rockwell Environmental Planner * Lynette E. Romig Environmental Planner Michael S. Donchez Transportation Planner Chetna A. Patel Transportation Planner Elaine A. Sales Administrative Assistant Gayle H. Turner Administrative Secretary * Alice J. Lipe Secretary Lorraine M. Heiser Receptionist/Secretary * Joseph A. Sandova Drafting Supervisor * Wilmer R. Hunsicker, Jr. Planning Technician Bonnie D. Sankovsky Drafter I **Project Planner *Staff for this report June 1999 TABLE OF CONTENTS Page List of Tables ................................................................................................... iii List of Figures ....................................................................................................iv Chapter 1. Introduction ................................................................................................. 1-1 2. Watershed Characteristics and Hydrologic Response........................................... 2-1 A. General Characteristics.................................................................................. 2-1 B. Hydrologic Response..................................................................................... 2-6 3. Little Lehigh Creek Watershed Land Development and Runoff Impacts ............. 3-1 A. General Land Development Impacts on Storm Runoff ................................. 3-1 B. Historical Little Lehigh Creek Watershed Development............................... 3-5 C. Future Little Lehigh Creek Watershed Development.................................... 3-7 4. Little Lehigh Creek Watershed Floodplain Information ....................................... 4-1 A. Floodplain Delineation.................................................................................. 4-1 B. Detailed Versus Preliminary Floodplain Delineation by Stream Segment.... 4-1 C. Existing and Future Floodplain Development............................................... 4-2 5. Little Lehigh Creek Watershed Existing Storm Drainage Problem Areas and Significant Obstructions.......................................................................... 5-1 A. Existing Storm Drainage Problem Areas....................................................... 5-1 B. Significant Obstructions................................................................................ 5-1 6. Storm Runoff Control Techniques ........................................................................ 6-1 A. Volume Controls............................................................................................ 6-2 1. Infiltration Pits and Trenches ................................................................. 6-2 2. Concrete Grid and Modular Pavement................................................... 6-4 3. Porous Asphalt Pavement....................................................................... 6-5 4. Grassed Waterways, Filter Strips, and Seepage Areas........................... 6-7 iv TABLE OF CONTENTS (cont’d) Chapter Page 6. (cont’d) B. Rate Controls 6-8 1. Detention Basins .................................................................................... 6-9 2. Parking Lot Storage.............................................................................. 6-10 3. Rooftop Detention................................................................................ 6-11 4. Cistern Storage ..................................................................................... 6-12 C. Nonstructural Storm Water Management Techniques................................. 6-13 7. Review of Storm Water Collection Systems and Their Impacts........................... 7-1 A. Existing Storm Water Collection Systems .................................................... 7-1 B. Future Storm Water Collection Systems ....................................................... 7-3 C. Existing and Proposed Flood Control Projects.............................................. 7-4 8. Runoff Control Philosophy and Performance Standards ...................................... 8-1 A. Runoff Control Philosophy............................................................................ 8-1 1. Release Rate Concept............................................................................. 8-2 2. Release Rate Determination ................................................................... 8-7 B. Performance Standards.................................................................................. 8-8 1. Description of Performance Standard Districts...................................... 8-8 2. Performance Standard Implementation Provisions ................................ 8-9 9. Municipal Ordinance to Implement the Little Lehigh Creek Watershed Storm Water Management Plan..................................................................... 9-1 10. Priorities for Implementation of the Plan............................................................ 10-1 11. Plan Review, Adoption and Updating Procedures .............................................. 11-1 iv LIST OF TABLES Table Page 1 Little Lehigh Creek Watershed Advisory Committee........................................... 1-3 2 Little Lehigh Creek Watershed Municipal Engineers Committee ........................ 1-4 3 Little Lehigh Creek Watershed Lawyers Advisory Committee ............................ 1-4 4 Little Lehigh Creek Watershed Square Mileage ................................................... 2-1 5 Little Lehigh Creek USGS Gaging Station Frequency Data................................. 2-6 6 Calibrated WATERSHED Peak Flow Values Versus Flow Targets from Gage Data .................................................................................................2-7 7 “Typical” Percent Imperviousness by Land Use ................................................... 3-1 8 Runoff Curve Number by Land Use Category...................................................... 3-4 9 Little Lehigh Creek Watershed Land Development 1972-1997 ........................... 3-6 10 Little Lehigh Creek Watershed Projected Land Development 1998-2008 .................................................................................................3-7 11 Little Lehigh Creek Watershed Flood Insurance Study Area................................ 4-1 12 Little Lehigh Creek Watershed Storm Drainage Problem Areas .......................... 5-3 13 Little Lehigh Creek Watershed Significant Obstructions ................................... 5-12 14 Man-Made Storm Water Conveyance Facilities Used as Reaches in the Little Lehigh Creek Watershed Hydrologic Model ............................. 7-2 15 Man-Made Reach Capacities versus WATERSHED Peak Flow Values.............. 7-3 16 Minimum Municipal Ordinance Requirements..................................................... 9-3 iv LIST OF FIGURES Figure Page 1 Little Lehigh Creek Watershed Location Map...................................................... 2-2 2 Little Lehigh Creek Watershed Map ..................................................................... 2-3 3 Little Lehigh Creek Watershed Geology............................................................... 2-4 4 Little Lehigh Creek Flood Frequency at Gage from USGS and Calibrated WATERSHED Model................................................................................... 2-8 5 Impact of Impervious Cover on Storm Runoff...................................................... 3-3 6 Detailed Versus Preliminary Flood Studies by Stream Segment .......................... 4-3 7 Little Lehigh Creek Watershed Problem Areas....................................................