Tibbetts Brook Wetland Restoration: Conceptual Plan The City of New York Department of Parks & Recreation Van Cortlandt Park, the Bronx, New York June 14, 2018 Tibbetts Brook Wetland Restoration: Conceptual Plan The City of New York Department of Parks & Recreation Table of Contents Executive Summary ......................................................................................................................... ES-1 1 Introduction ................................................................................................................................... 1 1.1 Project Scope ...................................................................................................................... 1 1.2 Project Location .................................................................................................................. 3 1.3 Conceptual Planning Approach: Process and Findings ..................................................... 4 1.3.1 Data Gathering, Organization, and Review............................................................ 4 1.3.2 Agency Input, Review, and Coordination ............................................................... 4 1.3.3 Community and Stakeholder Engagement ............................................................ 5 1.3.4 Project Goals and Objectives ................................................................................. 6 1.3.5 Key Project Deliverables ........................................................................................ 7 2 Background and Context .............................................................................................................. 8 2.1 Available Data ..................................................................................................................... 8 2.2 Site Characterization ........................................................................................................... 9 2.2.1 Historic Context ...................................................................................................... 9 2.2.2 Hydrology, Geomorphology and Water Quality ................................................... 10 2.2.3 Ecological Communities ....................................................................................... 13 2.2.4 Parallel Park Programs, Access and Uses .......................................................... 14 3 Design ......................................................................................................................................... 15 3.1 Design Inputs and Requirements ..................................................................................... 15 3.1.1 Topography ........................................................................................................... 15 3.1.2 Flow Regime ......................................................................................................... 15 3.1.3 Critical Water Surface Elevations ......................................................................... 16 3.1.4 Ponding and Localized Flooding .......................................................................... 17 3.1.5 Stormwater Detention ........................................................................................... 17 3.1.6 Connection Points (for Lake and Wetland Outflow) ............................................. 18 3.1.7 Connection Points for Future Opportunities ......................................................... 19 3.1.8 Water Quality Improvements ................................................................................ 19 3.2 Ecological Considerations ................................................................................................. 20 3.2.1 Sediment ............................................................................................................... 20 3.2.2 Soils ...................................................................................................................... 20 3.2.3 Ecological Communities ....................................................................................... 20 3.2.4 Invasive Species & Management Needs ............................................................. 20 3.3 Design Alternatives ........................................................................................................... 21 3.3.1 Description ............................................................................................................ 21 3.3.2 Hydrologic Flow Differences from Lake to Wetland ............................................. 22 3.3.3 Hydrologic Flow Differences within Tibbetts Wetland .......................................... 22 3.3.4 Wetland Cut and Fill Comparison......................................................................... 22 3.4 The Selected Design Alternative and 30% Design ........................................................... 23 3.5 30% Design Features ....................................................................................................... 25 3.5.1 Wetland Zones ..................................................................................................... 25 3.5.2 Proposed Elevations and Wetland Cut and Fill .................................................... 28 3.5.3 Stormwater Detention Potential ............................................................................ 29 3.5.4 Outlets and Flow Control Structures .................................................................... 30 3.5.5 Spillway ................................................................................................................. 35 3.5.6 Seepage Berm ...................................................................................................... 36 3.5.7 Microtopography ................................................................................................... 37 i June 14, 2018 3.5.8 Landscaping and Plant Material ........................................................................... 37 3.5.9 Utilities and Sewer Connection ............................................................................ 39 3.5.10 Boardwalk and Paths ............................................................................................ 39 3.5.11 Amenities and View Points ................................................................................... 40 3.6 30% Design Limitations and Data Analyses Required ..................................................... 40 3.6.1 Groundwater Elevations ....................................................................................... 40 3.6.2 Lake Bathymetry and Water Elevations ............................................................... 42 3.6.3 Water Budget and Projected Flows ...................................................................... 42 3.6.4 Outlet Structure Sizing and Design ...................................................................... 42 3.6.5 Pipe Verification .................................................................................................... 42 3.6.6 Utilities Verification ............................................................................................... 43 3.6.7 Reuse of Excavated Materials .............................................................................. 43 4 Proposed Conceptual Plan and Cost Estimate .......................................................................... 43 4.1 Design Objectives Met ...................................................................................................... 43 4.2 Cost Estimate .................................................................................................................... 43 5 Potential O&M Requirements ..................................................................................................... 45 5.1 Plantings............................................................................................................................ 45 5.2 Outlets ............................................................................................................................... 45 5.3 Boardwalk ......................................................................................................................... 46 6 Potential Opportunities for a Future Connection to the Harlem River along the Putnam Greenway ................................................................................................................................... 46 7 Next Steps .................................................................................................................................. 48 8 References.................................................................................................................................. 49 Tables Table 1. Community Outreach Activities................................................................................................ 6 Table 2. Key Project Deliverables .......................................................................................................... 8 Table 3. Critical Water Surface Elevations .......................................................................................... 16 Table 4. Comparison of Conceptual Design Alternatives and Existing Conditions ............................. 21 Table 5. Comparison of Tibbetts Brook Wetland Restoration Concepts—Cut and Fill....................... 23 Table 6. Preferred Alternative Concept Design Summary .................................................................. 25 Table 7.