ELLERBE CREEK GREEN INFRASTRUCTURE IMPLEMENTATION PLAN 4/22/16 Amanda Close, Christina Davis, & Bethany Williams Masters project submitted in partial fulfillment of the requirements for the Master of Environmental Management degree in the Nicholas School of the Environment of Duke University Dr. Julie DeMeester and Dr. James Heffernan, Advisors Mr. Chris Dreps (ECWA), Client Ellerbe creek green infrastructure implementation plan Ellerbe creek green infrastructure implementation plan AMANDA CLOSE, CHRISTINA DAVIS, & BETHANY WILLIAMS EXECUTIVE SUMMARY Ellerbe Creek is a degraded urban stream that runs through a large portion of Durham, North Carolina. The recent intensification of urban development has transformed the Watershed into a highly engineered system. Sections of the creek are piped underground and the entire creek is affected by impervious surfaces that cover one fourth of its catchment. Impervious surfaces prevent precipitation from infiltrating sloWly into the ground as it Would in a more natural, forested system. Instead, this Water rapidly runs off of the land, collecting pollutants and nutrients that accumulate on the surface of roads, sideWalks, and buildings. This has cumulatively impacted the Water quality and habitat health of Ellerbe Creek. The health of Ellerbe Creek is of particular importance because it drains into Falls Lake, a drinking Water source for the City of Raleigh and a regulated Waterbody under the North Carolina Department of Environmental Quality’s Falls Lake Nutrient Management Strategy. Green infrastructure (GI) has been pioneered in municipalities throughout the country to capture and treat runoff from impervious surfaces before it enters local streams and rivers. GI is an alternative stormWater treatment approach that seeks to emulate the Way in Which natural systems filter and transport water. Examples of GI include residential scale installation of cisterns, rain gardens, and doWnspout disconnection, as Well as larger scale commercial and industrial projects such as green roofs, green streets, and permeable pavement in parking lots. GI serves as an alternative to more engineered solutions, such as treatment facilities, reservoirs, and storm drains and pipes. In particular, GI Works by retaining Water during storm events and alloWing the Water to slowly infiltrate into the ground. This process removes pollutants from the water and reduces the amount of runoff that reaches local waterways during storms. The Durham-based non-profit organization, Ellerbe Creek Watershed Association (ECWA), was founded with the mission to improve the creek’s health for the benefit of the ecosystem and surrounding community. A large portion of ECWA’s efforts have focused on installing distributed green infrastructure projects throughout the watershed. In 2014 ECWA formed the Ellerbe Creek Green Infrastructure Partnership and executed a technical evaluation of the potential for GI implementation in doWntoWn Durham. This project Was developed to extend the Ellerbe Creek Green Infrastructure Partnership analysis into the Strayhorn Project Site, an area that is contiguous to the previously assessed area. This Was achieved through three objectives: Page 1 Ellerbe creek green infrastructure implementation plan 1) To identify commercial and industrial GI opportunities throughout the entire Ellerbe Creek Watershed through geospatial analysis. 2) To identify residential GI opportunities Within the Strayhorn Project Site through fieldWork. 3) To model the stormWater volume and nutrient reductions associated With each identified residential GI practice and to develop a tool for prioritization and scenario planning. Objective 1: To evaluate the potential for larger commercial and industrial green infrastructure opportunities throughout the Ellerbe Creek Watershed, geospatial analysis was utilized. To accomplish this, a tool developed by Ben Green (2015) Was used to identify green street, green roof, and permeable parking lot opportunities across the Watershed. This tool Was adapted for the particular data available in Durham County. The result of this analysis Was the identification of 4,728 commercial and industrial green infrastructure retrofit opportunities in Ellerbe Creek Watershed. Fifty-one of these potential projects were located Within the Strayhorn Project Site. Geospatial analysis Was further used to create an Urban Watershed Delineation tool. This tool uses digital elevation models to delineate the natural topographic Watershed at any user-selected point in the Ellerbe Creek Watershed. The tool also evaluates the presence of stormWater infloW points or pipes to identify stormWater contributions to the natural Watershed. The combined contribution of stormWater flow and topographic floW are merged to create an urban Watershed. Furthermore, the tool identifies property ownership data for this Watershed. This tool can be used by ECWA to determine Where GI projects should be implemented to improve Water quality at any given point in the Watershed. Objective 2: To evaluate residential retrofits Within the Strayhorn Project Site that geospatial analysis Was unable to detect, a field methodology Was developed. Each parcel was evaluated individually for potential downspout disconnection, rain garden, and cistern opportunities. The presence of downspouts, current connectivity to the stormWater system, surrounding topography, and available open space Within the parcel Were all key considerations to Whether a retrofit Was recommended. A suite of data Was collected for each parcel using a mobile mapping application including latitude, longitude, and drainage area contributing to the proposed GI retrofit. All of the data Was recorded on a digital field form, Which Was later exported to Excel and ArcGIS for analysis. In total, 223 retrofit opportunities were identified: 56 rain gardens, 61 downspout disconnections, and 106 cisterns. Objective 3: The stormWater improvement capabilities of each rain garden and cistern opportunity were modeled using the Jordan/Falls Lake Stormwater Nutrient Load Accounting Tool. Outputs of the tool included the volume of stormWater treated and the associated nitrogen and phosphorus removal capabilities of each individual project. An optimization tool Was built to aid ECWA in scenario planning and decision-making using the field data and model results. Upon inputting constraints, the optimization tool performs a cost effectiveness analysis, ultimately recommending a list of projects that will treat the largest volume of stormWater While also satisfying the given constraints. These projects are cross-referenced to the GIS map for easy identification and spatial analysis. In conclusion, this project effectively extended the identification of green infrastructure retrofit opportunities within Ellerbe Creek Watershed. The creation of the Urban Watershed Delineation tool and the optimization tool Will alloW ECWA to implement the most cost effective projects at the most effective locations for stormWater treatment. ECWA has already begun community outreach efforts in the Strayhorn Project Site using the field data generated during this project. The results of this analysis present ECWA with a streamlined process for implementing these practices and furthering their ultimate goal of improving Ellerbe Creek’s health for the benefit of the residents of Durham. Page 2 Ellerbe creek green infrastructure implementation plan Table of Contents Executive Summary................................................................................................................................1 Introduction...........................................................................................................................................4 Urban Stream Syndrome .............................................................................................................................. 4 StormWater Management and Green Infrastructure ................................................................................... 4 Ellerbe Creek Watershed .............................................................................................................................. 6 Objectives ................................................................................................................................................... 10 MetHods.............................................................................................................................................. 10 Geospatial Methods: Urban Watershed Delineation Tool.......................................................................... 10 Geospatial Methods: Green Infrastructure Retrofit Scoping Tool.............................................................. 12 Field Methods ............................................................................................................................................. 13 Prioritization Methods: Modeling StormWater Volume, Nitrogen, and Phosphorus Reductions............... 17 Prioritization Methods: Optimization Tool Development .......................................................................... 19 Results ................................................................................................................................................ 21 Geospatial Results: Urban Watershed Delineation Tool............................................................................. 21 Geospatial Results: Green Infrastructure Retrofit Scoping Tool................................................................