Nancy Creek Watershed Improvement Plan SUMMER 2016 Prepared for the City of Brookhaven, Georgia City of Brookhaven Nancy Creek Watershed Improvement Plan TABLE OF CONTENTS List of Tables .................................................................................................................................................................. 4 List of Figures ................................................................................................................................................................ 5 Acknowledgements ........................................................................................................................................................ 7 Executive Summary ....................................................................................................................................................... 8 Chapter 1: Background ................................................................................................................................................ 12 1.1. Objectives ......................................................................................................................................................... 12 1.2. Watershed Description ..................................................................................................................................... 12 1.2.1. Subwatersheds .......................................................................................................................................... 13 1.3. Land Use .......................................................................................................................................................... 17 1.4. Water Quality Concerns .................................................................................................................................... 19 1.4.1. State 303(d) List of Impaired Waters ......................................................................................................... 19 1.4.2. Total Maximum Daily Loads ...................................................................................................................... 20 1.4.3. Other Watershed Concerns ....................................................................................................................... 20 1.4.4. Murphey Candler Lake .............................................................................................................................. 23 1.5. Regulatory Framework ..................................................................................................................................... 24 1.5.1. Municipal Separate Storm Sewer System (MS4) Permit ........................................................................... 24 1.5.2. Metropolitan North Georgia Water Planning District (MNGWPD) .............................................................. 24 1.5.3. DeKalb County Watershed Protection Plan ............................................................................................... 25 1.5.4. Georgia Rules for Dam Safety................................................................................................................... 25 1.6. Watershed Improvement Plan Development Process ...................................................................................... 26 1.7. Watershed Improvement Plan Overview .......................................................................................................... 26 Chapter 2: Watershed Investigation and Analysis ........................................................................................................ 27 2.1. Assessment of Available Water Quality Data ................................................................................................... 27 2.2. Watershed Modeling of Baseline Conditions .................................................................................................... 31 2.2.1 Model Inputs ............................................................................................................................................... 33 2.2.2. Model Calibration and Results ................................................................................................................... 33 2.3. Stream Walk Methodology and Results ............................................................................................................ 36 2.3.1. Stream Walk Methodology ........................................................................................................................ 36 2.3.2. Results ...................................................................................................................................................... 38 2.4. Murphey Candler Lake Sampling ..................................................................................................................... 40 2.4.1. Murphey Candler Lake Water Chemistry Sampling Results ...................................................................... 40 August 2016 Page 2 City of Brookhaven Nancy Creek Watershed Improvement Plan 2.4.2. Murphey Candler Lake Water and Sediment Depth Measurements ......................................................... 42 2.4.3. Murphey Candler Lake Shoreline Conditions ............................................................................................ 44 2.4.4. Overall Lake Health for Murphey Candler Lake ........................................................................................ 47 2.5. Limited Upland Conditions Assessment ........................................................................................................... 48 2.6. Summary of Findings ........................................................................................................................................ 50 Chapter 3. Watershed Improvement Projects and Programs ....................................................................................... 51 3.1. Watershed Improvement Goals ........................................................................................................................ 51 3.2 Process to Identify Projects ............................................................................................................................... 52 3.3. Recommended Watershed Improvement Projects ........................................................................................... 53 3.3.1. Stream Enhancement Projects .................................................................................................................. 53 3.3.2. BMP and BMP Retrofit Projects ................................................................................................................ 56 3.3.3. Murphey Candler Lake Recommended Projects ....................................................................................... 61 3.4. Future Conditions Model Results ...................................................................................................................... 66 3.4.1. Future Conditions Model Results .............................................................................................................. 66 3.5. Impervious Retrofit Assessment Areas ............................................................................................................. 67 3.6 Existing Watershed Programs and Recommendations ..................................................................................... 71 3.6.1. Enforcement of Existing Ordinances ......................................................................................................... 71 3.6.2. Public Education and Outreach and Public Involvement ........................................................................... 72 3.6.3. Infrastructure Inventory and Condition Assessment .................................................................................. 73 3.6.4. Inspection of Stormwater Management Facilities ...................................................................................... 73 3.6.5. City Maintenance Activities........................................................................................................................ 74 3.6.6. Regional Watershed Coordination ............................................................................................................. 74 3.6.7. Implementation Tracking ........................................................................................................................... 74 Chapter 4: Implementation Plan ................................................................................................................................... 75 4.1. Implementation Costs ....................................................................................................................................... 75 4.1.2. Recommended Project Cost Estimation Methodology and Assumptions .................................................. 75 4.1.2. Planning Level Costs for the Recommended Projects .............................................................................. 77 4.1.3. Recommended Retrofit Assessment Cost Estimation Methodology and Assumptions ............................. 78 4.2. Grant Funding and Financing ........................................................................................................................... 79 4.2.1. Grant Funding ..........................................................................................................................................