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.

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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...... 21 Field Results for the Strayhorn Project Site ...... 29 Prioritization Results...... 31 Discussion ...... 32 Future Directions ...... 34 Conclusions ...... 35 Acknowledgements ...... 37 References ...... 38 Appendix A: Urban watershed delineation user manual...... 41 Appendix B: Green infrastructure retrofit Scoping tool methods...... 48 Appendix C: residential retrofit field data collection form ...... 50 Appendix D: Residential Retrofit Optimization Tool...... 58 Anatomy of the Tool ...... 58 Example Tool Run ...... 59 Potential Uses ...... 64

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INTRODUCTION

Urban Stream Syndrome Concrete, steel, and pavement all impede water’s ability to infiltrate into the ground where it can either recharge stores of groundwater or return to streams via underground flow paths (Dunne & Leopold, 1978). Regardless of the route a raindrop takes through the ground, the process of infiltration acts as a natural purification mechanism because impurities in the water sorb to soil, sediment, and gravel (Murakami et al, 2008). When urban development decreases the available surface area for infiltration, a greater amount of water from precipitation events runs off overland (Holman-Dodds, 2003). This stormwater collects nutrients like nitrogen and phosphorus, oil, heavy metals, chemicals, and trash, and then deposits the load in nearby streams in intense, episodic events (Lopes et al, 1995). In excess, stormwater can severely degrade water quality and aquatic life, heighten flood risks, and decrease shallow groundwater storage that feeds stream baseflow during dry periods. This phenomenon, which has been increasingly observed in recent years, has been termed the Urban Stream Syndrome (Walsh et al, 2005).

Stormwater Management and Green Infrastructure In 1987, the Federal Clean Water Act was amended by Congress to include the regulation of non- point source discharges entering waters of the United States (Franzetti, 2005). Under Phase I of EPA’s implementation of this amendment, municipal separate stormwater systems (MS4s) serving populations of 100,000 or more are required to obtain a National Pollutant Discharge Elimination System (NPDES) permit (Franzetti, 2005). The MS4 for the City of Durham falls within this category. Therefore, they are required to manage a NPDES permit from the North Carolina Department of Environmental Quality (NCDEQ) to discharge into the Neuse River and Cape Fear River watersheds (City of Durham, 2011). The permit states that the City must “control to the maximum extent practical the discharge of pollutants from its municipal storm sewer system associated with stormwater runoff” (NC Water Quality Division, 2013). Currently, the City of Durham meets this requirement by implementing and updating its Stormwater Management Program Plan that addresses public outreach and participation, illicit discharge elimination, construction and post-construction stormwater management, and pollution prevention for municipal operations (City of Durham, 2011).

Page 4 Ellerbe creek green infrastructure implementation plan Traditionally stormwater has been mitigated by piping, channelizing, capturing, and treating flows - methods termed “gray infrastructure”. The current degradation of urban streams nationwide speaks to the need for innovation in stormwater management technologies. Green infrastructure encompasses a suite of technologies that can be used in place of, or in combination with, conventional gray infrastructure to achieve desired outcomes of stormwater retention or water quality restoration. Green infrastructure emulates the natural properties of soil and vegetation to infiltrate, store, filter, evaporate, and transpire water, reintroducing key elements of a site’s water balance and slowing overland flow. These practices are often site-specific and include green roofs, engineered bioretention like rain gardens and bioswales, permeable pavement, rainwater harvesting, downspout disconnections, and land preservation.

The following descriptions of practices are summarized from EPA, 2014 Green Infrastructure website. Engineered bioretention incorporates highly porous soils and herbaceous plants into shallow basins to capture and store urban runoff. Plants are used to create a surface ponding effect, allowing water to soak through mulch and sand layers. The retained stormwater can then slowly infiltrate into the surrounding soil. Bioretention basins are preferable along sidewalks, road medians, parking lots, or in residential yards, often taking the form of rain gardens. Green roofs are another form of bioretention, where rooftop space is vegetated to temporarily store rainwater and promote evapotranspiration. Bioretention can be used in concert with permeable pavement, a practice that allows infiltration through pervious concrete, asphalt, and pavers while also serving utilitarian needs. Similar to bioretention practices, bioswales collect water in vegetated basins but differ in that they are typically linear features that transport water through a shallow soil layer. Rather than promoting infiltration, rainwater harvesting practices use cisterns to collect rainwater and store it for later use. These cisterns vary significantly in size and therefore can be used at residential or commercial scales. Downspout disconnection is the process of rerouting roof runoff away from storm drains and into bioretention areas or cisterns. Land conservation refers to the protection of large swaths of undeveloped land to offset urban degradation by maintaining a natural hydrologic regime nearby.

Not only is green infrastructure a potential solution to issues of stormwater management, it is also often less of an economic burden than traditional infrastructure. By opting for a combination of green and gray infrastructure, Cincinnati will save a projected $150 million in their efforts to control combined sewer overflows (EPA, 2014). The City of Philadelphia completed a comprehensive cost-benefit analysis of alternative strategies to their combined sewer overflow problem and estimated their 40 year savings to be

Page 5 Ellerbe creek green infrastructure implementation plan between $1.9 and $4.5 billion depending on the extent of impervious surfaces retrofitted (EPA, 2014). As Durham grapples with managing its stormwater, a combination of traditional and green infrastructure should be explored to cultivate a cost effective and sustainable solution to the urban stream syndrome.

Ellerbe Creek Watershed Ellerbe Creek flows from its headwaters in northeast Durham, North Carolina to its confluence with Falls Lake Reservoir, a significant source of drinking water for Raleigh and other nearby communities (Figure 1). Its 37 square mile watershed drains nearly half of Durham, including a highly developed downtown area (Dreps et al, 2014). In 2013, more than 22% of Ellerbe Creek Watershed was covered with impervious surfaces - a large enough proportion to drastically alter the natural hydrologic regime and threaten drinking water quality in Falls Lake (NCDENR, 2013). In 2010, the North Carolina Water Quality Division measured heightened levels of nutrients, suspended sediment, heavy metals, oil, and biochemical oxygen demand in Ellerbe Creek and therefore classified the waterway as “impaired”. The Division noted that the likely cause of such contamination is urban stormwater (NC Water Quality Division, 2010).

Figure 1: Map of Ellerbe Creek Watershed (outlined in red) in the context of North Carolina’s Triangle Region. Image courtesy of City of Durham Stormwater Services and Brown and Caldwell.

Page 6 Ellerbe creek green infrastructure implementation plan The state developed a Falls Lake Nutrient Management Strategy in 2011, which requires a 77% reduction of phosphorous and a 40% reduction of nitrogen (NCDENR, 2011). This translates into reductions of 7.4 lbs/acre/year of total nitrogen and 0.38 lbs/acre/year of total phosphorus (Brown and Caldwell, 2010). Because Ellerbe Creek is a major contributor to the nutrient load in Falls Lake, intervention by the City of Durham is necessary. In 2010, the City contracted Brown and Caldwell to develop a Watershed Improvement Plan for Ellerbe Creek. The plan outlined management scenarios for nutrient reduction that cost between $56 and $430 million (Brown and Caldwell, 2010). Only the highest cost scenario came close to meeting the Falls Lake Strategy obligations, as it is modeled to reduce nitrogen by 33% and phosphorus by 38% (Brown and Caldwell, 2010). This scenario involves the implementation of 16 large scale BMPs like constructed wetlands and bioretention, 16 stream restoration projects, and $60 million worth of sanitary sewer system rehabilitations and nutrient controls at the North Durham Wastewater Reclamation Facility (Brown and Caldwell, 2010). These gray infrastructure improvements alone are capable of reducing nitrogen by 4% and phosphorus by 19% (Brown and Caldwell, 2010). However, this scenario is still an attractive option as it is highly effective at removing fecal coliform; models project a 59% reduction with this scenario (Brown and Caldwell, 2010). As none of the scenarios fully achieve the required reductions under the Falls Lake Nutrient Strategy, it is important for the City to determine alternative stormwater control measures that can supplement potential gray infrastructure projects and large-scale, centralized BMPs. In recent years, pioneering work has been completed at the local scale that illuminates a sustainable alternative to traditional stormwater mitigation methods, green infrastructure. In 2014, Ellerbe Creek Green Infrastructure Partnership completed an intensive study that quantified the reductions in stormwater volume and pollutant loading from a proposed distribution of green infrastructure retrofits for a small (467 acre), ultra-urban catchment in South Ellerbe Creek. The results suggest that 57.3 million gallons of stormwater can be captured on an annual basis and nitrogen and phosphorus removal rates could climb to 38% and 43% respectively (Dreps et al, 2014).

Ellerbe Creek Watershed Association Ellerbe Creek Watershed Association (ECWA) is a non-profit in Durham whose mission focuses on the wellbeing of Ellerbe Creek. ECWA envisions a living creek connecting human and natural communities in Durham (ECWA Vision Statement, 2016). This mission is achieved by working towards three pillars of work: protecting, restoring, and connecting the community to Ellerbe Creek. A large portion of the restoration work includes their investment in dispersed green infrastructure practices throughout the community. It is

Page 7 Ellerbe creek green infrastructure implementation plan through this avenue that this project seeks to improve the health of Ellerbe Creek and to further ECWA’s efforts and mission.

The abilities of GI to reduce both stormwater volume and nutrient loading into Ellerbe Creek have valuable implications for furthering ECWA’s mission. Additionally, there are ancillary benefits of green infrastructure that go beyond water quality improvements. These include community engagement, stormwater education, developing a sense of neighborhood pride and identity, aesthetic value, carbon sequestration and urban cooling for vegetated practices, and mental and physical health benefits. Although these ancillary benefits are difficult to quantify, this does not diminish their importance. While gray infrastructure, like stormwater treatment plants, filtration methods, and storm drain improvements, can also be effective at mitigating pollution issues caused by excess stormwater, they do not offer the suite of community benefits that green infrastructure practices can provide. Because ECWA takes a holistic approach to watershed planning, green infrastructure is a promising avenue to enhance the well-being of Ellerbe Creek and the surrounding community.

Green Infrastructure in Ellerbe Creek Watershed Because ECWA highly values the ancillary benefits that green infrastructure provides and has already developed a level of capacity to implement small-scale GI, this analysis solely considered residential and commercial GI retrofits. It is also intended to be an extension of Ellerbe Creek Green Infrastructure Partnership’s efforts to identify sites for green infrastructure retrofits in downtown Durham which considered rainwater harvesting, green streets, green roofs, and rain gardens. Furthermore, this project included a geospatial analysis component that sought to identify opportunities for larger scale commercial and industrial GI practices. This geospatial analysis was the first effort of its kind to identify such opportunities across the entire Ellerbe Creek Watershed. There are many other effective methods of stormwater mitigation, but for the aforementioned reasons, this analysis did not focus on other strategies as the organization had already built political and community momentum as well as organizational capacity for green infrastructure implementation in Durham. The scope of this analysis is limited to the identification of sites for large-scale green infrastructure in Ellerbe Creek Watershed through geospatial analysis, fine- scale GI site identification for residential retrofits in the study area referred to as the “Strayhorn Project Site” via field work, and developing a prioritization and decision-support methodology for ECWA to use when planning for project implementation.

Page 8 Ellerbe creek green infrastructure implementation plan Strayhorn Project Site The Strayhorn Project Site is a 134-acre sub-catchment of the Ellerbe Creek Watershed that is located north of, and directly abuts, the land previously assessed by the Ellerbe Creek Green Infrastructure Partnership (Figure 2). This 134-acre catchment will be referred to as the “Project Site” for the remainder of this report. The Project Site primarily consists of residential parcels, and thus has a significant potential for residential-scale dispersed green infrastructure retrofits, and conditions that are less suited for the implementation of commercial and industrial retrofits. Given that residential areas are largely constrained by space and the amount of development on each parcel, green infrastructure represents an opportunity to reduce stormwater volume in these areas that are otherwise limited in their capacity for traditional stormwater volume reduction technologies.

Figure 2: Map displaying the urban watershed and Strayhorn Project Site boundaries.

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Objectives For this project, we worked with ECWA to identify dispersed green infrastructure retrofits to address the long-term goal of improving water quality in Ellerbe Creek. At the completion of this project, our findings will allow ECWA to build and implement the identified projects. Our objectives were as follows:

1) Use geospatial analysis to identify large-scale commercial and industrial green infrastructure opportunities (green roofs, green streets, and permeable parking lots) for the entire Ellerbe Creek Watershed, and to create a GIS-based tool to delineate urban sub-catchments across the watershed. 2) Use fieldwork to identify residential green infrastructure practices (cisterns, rain gardens, and downspout disconnections) for the parcels within the Strayhorn Project Site. 3) Develop a prioritization tool that identifies the best residential GI opportunities based on cost-effectiveness ratios and other project constraints, such as budget.

METHODS

Geospatial Methods: Urban Watershed Delineation Tool Urban watersheds are complex since the quality of a water body is determined by both runoff from impervious and pervious surfaces, and the stormwater that is piped into the system. To facilitate ECWA’s ability to determine the best locations for future green infrastructure projects, an ArcGIS-based tool was created that allows the user to determine the stormwater pipe contribution and the natural watershed flow contribution to a given point. Furthermore, the tool outputs the user parcel ownership data for the delineated urban watershed, thus facilitating ECWA’s communication with landowners to gauge interest in GI opportunities. The tool was developed with Python language scripting (Python Software Foundation, 2015). This allowed for the most control over the data inputs, user inputs, and expected outputs, while also ensuring transferability from one computer system to another.

To prepare data for this tool, 20 foot resolution Digital Elevation Model (DEM) imagery was downloaded for Ellerbe Creek Watershed (North Carolina Flood Risk Information System, 2007). This data was converted from asc format to a raster, and then was merged and clipped to the shape of Ellerbe Creek Watershed. This DEM was filled, then flow accumulation and flow direction were computed. Next, a 60 foot

Page 10 Ellerbe creek green infrastructure implementation plan buffer around stormwater inflow points and pipes for the entire Ellerbe Creek Watershed was created (Duke University Libraries, 2010). This was used to determine if there are urban stormwater contributions to the natural watershed. A summary of these data inputs and the tool workflow have been detailed in Table 1 and Figure 3 respectively. Table 2 shows the user inputs required to run the tool. For a comprehensive user guide, refer to Appendix A.

Table 1: Data inputs For the Urban Watershed Delineation Tool

Data Inputs Data Type Data Source 20 ft. resolution Digital Elevation Model (DEM) of the North Carolina Flood Risk

Ellerbe Creek Watershed Information System (2007) 60 ft. buffer of all stormwater pipes and inflow points in the Duke University Libraries (2010)

Ellerbe Creek Watershed A flow accumulation raster derived from the DEM; a raster North Carolina Flood Risk was created to show where flow accumulation is greater Information System (2007) and than 500 contributing pixels (to direct the user on areas to ArcMap (2015) click on the map) County of Durham property ownership data NC One Map (2015)

Figure 3: The workflow used in the urban watershed delineation tool.

Page 11 Ellerbe creek green infrastructure implementation plan To run this tool, the user must first choose the point that they would like to delineate the urban watershed for. This point is defined by the user and is called a “pour point.” This means that the watershed is delineated based on the area of the land that eventually drains to this point. A snap distance of 30 was used in this tool, meaning that the tool will adjust the location of the pour point to the cell with the most flow accumulation within the closest 30 cells to the user-defined pour point. These cells were 20 by 20 feet in size. This snap distance of 30 was determined to work well with the data available for Ellerbe Creek Watershed, and is therefore recommended for use in this tool. This ensures that the user does not have to click on the map at an exact location for the tool to be able to run. The tool will adjust the location of this point for optimal results.

This tool was used to delineate the Project Site watershed for the Strayhorn catchment. The pour point that was used in this analysis is represented by the star on the map in Figure 2. The area of this watershed was converted into an area constrained by street blocks to allow for logical field data collection. The final acreage of the field Project Site was 134 acres. Boundaries for both the urban watershed and field Project Site are displayed in Figure 2.

Table 2: Inputs that the user must specify to run the Urban Watershed Delineation Tool.

Required User Inputs

The user must click on the map to select the pour point they are interested in; a default location of the pour point of the Strayhorn project site can be used Specify the snap distance for the user selected pour point. This adjusts the location of the pour point to make sure it fits the flow accumulation paths; a value of 30 is suggested Name for the urban watershed shapefile Name for the parcel information shapefile and Excel file

Geospatial Methods: Green Infrastructure Retrofit Scoping Tool An analysis was conducted to identify large-scale commercial and industrial green infrastructure retrofits within the entire Ellerbe Creek Watershed by using the Green Infrastructure Retrofit Scoping Tool developed by Ben Green (2015). The Green Infrastructure Retrofit Scoping Tool was created based on an interpretation of the Center for Watershed Protection’s Urban Stormwater Retrofit Practices by the Ellerbe Creek Green Infrastructure Partnership (Dreps et al, 2014; Schueler et al, 2007). The following Green Infrastructure Retrofit Scoping tools were adapted and utilized for Ellerbe Creek Watershed: large parking lots, small parking lots, individual rooftops, and green streets. Slight modifications from the original Green

Page 12 Ellerbe creek green infrastructure implementation plan Infrastructure Retrofit Scoping Tool were necessary to adapt it for the different datasets available for Ellerbe Creek Watershed (Green, 2015). These changes have been detailed in Appendix B.

The tool identified both large and small parking lots for permeable parking lot retrofits. To be considered for retrofits, large parking lots had to be greater than five acres in size and within fifty meters of a public open space parcel. This public open space area was necessary to allow for bioretention areas where water could overflow if the infiltration capacity of the parking lot had been met. Small parking lots were those that were less than 5 acres in size and were not on a residential parcel. This constraint was used to eliminate the identification of driveways on residential properties.

Individual rooftops greater than 0.25 acres were identified for green roof retrofits. It is important to note that this analysis did not include the slope of the roof or the ability of the roof to bear weight. These would be important constraints for the actual installation of green roof retrofits. Finally, the green street retrofit identification included curb setbacks, areas within the curb and right-of-way where bioretention practices could be installed, permeable pavement parking lanes, and bioretention areas where water would be able to overflow into a stormwater inlet point in the event that the infiltration capacity of the street had been met.

Field Methods The goal of fieldwork was to identify green infrastructure retrofit opportunities that could not be identified using GIS and satellite imagery. The methods described were conducted in the Project Site (Figure 2). Due to the residential nature of the site, fieldwork focused on identifying opportunities for rain gardens, cisterns, and downspout disconnections. Prior to starting fieldwork, ArcMap was used to generate a set of unique site ID numbers that were assigned to each parcel within the study area. To aid in the logistics of data collection and management of multiple field crews, the study site was divided into seven zones (Figure 4a). Field maps for each zone were produced to a resolution sufficient to allow for navigation and for taking roof area measurements in the field (Figure 4b). Maps were saved as geo-referenced PDFs and exported to the PDF Maps mobile application. A field data collection form was created using Google Forms technology (Google, 2015). Google Forms allows users to create customized surveys and data collection forms; information collected is automatically exported to an attached spreadsheet that can later be opened in Microsoft Excel for analysis.

Page 13 Ellerbe creek green infrastructure implementation plan The Center for Watershed Protection’s “Retrofit Reconnaissance Investigation Form” (2007) was used as a template, but was changed to reflect the residential nature of the project site and the objectives of this study. Pages were created to collect data for the three residential retrofit types of interest: rain gardens, cisterns, and downspout disconnections. The digital form included a site introductory page, with questions such as latitude and longitude, parcel address, and number of downspouts, as well as and an overall site page, which included questions such as the level of property maintenance and potential conflicts with utilities. For a copy of the entire form, refer to Appendix C.

Figure 4: Field maps were created to aid in the data collection process. Map A (left) displays the Project Site divided into 7 zones, and Map B (right) displays Zone 1. A map of each zone was created at a resolution sufficient to allow for field measurements using the PDF Maps app.

PDF Maps mobile app (Avenza, 2016) was also integral to fieldwork, and used for both navigation and data collection purposes. The geo-referenced base maps created for each zone allowed the movements of field crews to be tracked, and enabled them to consult the map for directions and to identify which parcel (labeled by site ID on the basemap) they were about to sample. The app also provided latitude

Page 14 Ellerbe creek green infrastructure implementation plan and longitude coordinates for each parcel, which were inputted into the digital field form. The most important feature of PDF Maps was the measure tool. This allowed field crews to take approximate area measurements in the field. Fieldwork was conducted in teams of two and occurred over the course of five weekends, totaling 69 collective hours. IPads and smartphones were used to collect the field data. Each parcel within the study area was assessed individually. A common work protocol was established to ensure that different field crews assessed parcels using the same methodology (Figure 5). All work was conducted from the sidewalk and street level, since crews did not have permission to access private property. Thus all decisions regarding retrofits were made based on visual information gathered from this vantage point. Upon arriving at a parcel the land was first assessed for homes or permanent structures. If the parcel was empty, the site ID number was recorded and field teams did not collect further data for that parcel. If a building was present, its gutters were assessed. The presence of gutters is crucial for all three of the GI retrofits, since they act to convey runoff away from the storm drain and into the retrofit. Homes without downspouts were not considered further. The connectivity of the downspouts to the city sewer system was assessed next. Downspouts that were already disconnected (i.e. runoff from the roof was funneled overland and not conveyed underground via pipes) were eligible for rain gardens or cisterns. Connected downspouts were also eligible for these retrofits, and in cases where these were not appropriate, were also considered for simple disconnection. For a downspout to be eligible for a rain garden retrofit, adequate open space at least ten feet from the foundation of the home had to be present (due to potential flooding hazards). Adequate open space meant that the area was large enough to treat the volume of runoff expected from the contributing drainage area. The drainage area was comprised of both roof and lawn area, and was measured in the field using the measure tool in PDF Maps. Minimum rain garden size was calculated by summing 10% of the impervious drainage area and 1% of the pervious drainage area. This approximate sizing guideline was a standard convention used by ECWA in the past (Chris Dreps, personal communication, 2015). Rain gardens were not recommended on parcels lacking the necessary area. Cisterns were recommended for downspouts if adequate space beneath the downspout was present. Three cistern sizes were considered: 100, 200, and 360 gallons. Areas requiring minor landscaping (i.e. pruning back bushes) were considered, but areas covered with dense vegetation that would require removal, were not. The PDF Maps app was used to measure the approximate roof area contributing to the downspout(s) servicing the cistern. This data was recorded in the digital field form.

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Are downspouts present?

Yes No

Are downspouts No GI retrofit disconnected? opportunities

Yes No

Is there sufficent Does topography open space for a properly sized rain allow disconnection? garden?

Yes No Yes No

Is there space Disconnection Rain Garden below the No GI retrofit downspout for a retrofit retrofit opportunity opportunity* opportunity cistern?

Yes No

Cistern retrofit No GI retrofit opportunity opportunities

*Downspouts eligible for disconnection were next evaluated for rain garden and cistern opportunities.

Figure 5: Workflow diagram that displays the methodology that crews used to identify potential retrofits in the field.

Page 16 Ellerbe creek green infrastructure implementation plan Downspout disconnection was the final retrofit opportunity examined. As mentioned previously, this retrofit was only possible on parcels with downspouts that were currently connected to the stormwater network. Topography and density of homes were the two factors limiting disconnection feasibility. For a downspout to be eligible, its outflow had to slope away from the foundation of the house to prevent flooding. The runoff also had to be directed away from neighboring parcels, and thus sufficient space for runoff to infiltrate naturally was necessary. Downspouts that were deemed eligible for disconnection were further evaluated to determine if a rain garden or cistern retrofit was possible, based on the constraints previously defined. If one of these retrofits were appropriate, it superseded the disconnection recommendation since rain gardens and cisterns are known to more effectively manage stormwater runoff (Chris Dreps, personal communication, 2015). Thus all disconnection opportunities recorded in the field were on downspouts that could not support a rain garden or a cistern. After all of the parcels within the Project Site were assessed in the field, the data collected using the Google Form was exported into Microsoft Excel (2010). In Excel, the data was cleaned so that each row represented a single recommended retrofit. These retrofits were then exported into ArcMap for spatial analysis.

Prioritization Methods: Modeling Stormwater Volume, Nitrogen, and Phosphorus Reductions As a part of the Falls Lake Rules, the North Carolina Division of Water Resources was required to produce a tool that would allow developers to estimate the nutrient loading that new developments generate and the nutrient reductions that Best Management Practices (BMPs) could achieve. The first version of this tool, Jordan/Falls Lake Stormwater Nutrient Load Accounting Tool (JFSLAT) 1.0, was developed collaboratively by the Division and the North Carolina State University Stormwater Team. Version 2.0 was released in 2013 and corrected several errors that appeared in the original version. JFSLAT version 2.0 was used to model stormwater volume and nutrients reductions on a per retrofit basis for this analysis. Unfortunately, the tool does not include modeling capabilities for downspout disconnection practices alone (those that are not subsequently connected to a rain garden or cistern). In addition, contributing area data was not collected for the large-scale retrofits identified by the Scoping Tool, which are necessary data inputs to run JFSLAT. Because of this, the opportunities for downspout disconnections that were identified in the field as well as large-scale retrofits identified via ArcGIS were not included in the modeling and prioritization analysis.

Page 17 Ellerbe creek green infrastructure implementation plan Several parameters are required to run JFSLAT: physiographic/geologic region, soil hydrologic group, and precipitation location. The model provides a map of the North Carolina physiographic regions that depicts southern Durham County as part of the Triassic Basin region (NCDENR, 2011). A previous study by the Ellerbe Creek Green Infrastructure Partnership identified the predominant soil type in the area as Urban and White Store Urban Land Complex, which are classified as hydrologic soil group D (Dreps et al, 2014). Carrboro was used as the precipitation location as it is the closest to the study site.

The following discussion of the JFSLAT model is an adapted version of the User’s Manual for the tool (NCDENR, 2011). To calculate runoff volumes, the model uses literature and field measured values to assign imperviousness percentages and calculate runoff coefficients for each land use input. The total annual runoff is determined by the area of each land use, the runoff coefficients, and the annual precipitation depth based on the precipitation location parameter. For the catchment-scale event mean concentrations (EMC) of total phosphorus (TP) and total nitrogen (TN), EMCs for each nutrient are assigned to each land use classification based on the existing literature. Residential roofs are modeled with a TN EMC of 1.08 mg/L and a TP EMC of 0.15 mg/L (NCDENR, 2011). A representative event mean concentration for the catchment is then calculated based on the proportion of each land use and the corresponding EMC. The average annual rainfall depth, the runoff coefficient, and the catchment representative EMC are used to calculate annual nutrient loading values.

The model determines the performance of BMPs with the input changes in land use and literature values of the effectiveness of each BMP under the input soil and physiographic conditions. The calculations for rainwater harvesting did not incorporate a land use change component, but each rain garden that was modeled included the amount of lawn area that would be converted to the rain garden area. The volume reduction percentages of rainwater harvesting and of bioretention without internal water storage (IWS) under hydrologic soil group D and Triassic Basin physiographic conditions were modeled as 50% and 15%, respectively (NCDENR, 2011). The model uses these percentages and the new land use areas to model the nutrient loading that would occur if the retrofit was implemented.

The model is intended for new or existing developments that are planning to incorporate green infrastructure (NCDENR, 2011). Because of this, the tool is set up such that the total development area and BMP catchment area can be entered as different sizes. To model the nutrient and stormwater volume reduction capabilities of each identified green infrastructure retrofit opportunity, it was assumed that the total development area and the retrofit catchment area are the same. The field estimates of contributing

Page 18 Ellerbe creek green infrastructure implementation plan roof and lawn area were used as the total development area and the total area treated by the BMP. While this method is helpful in determining the effectiveness of each individual practice, it assumes that connectivity in the watershed is negligible. This means that each modeled rain garden or cistern practice is assumed to be hydrologically isolated from every other practice or the reductions in stormwater and nutrients of one practice does not affect any other practice’s ability to reduce stormwater and nutrients. In an urban context, and particularly at a sub-parcel scale, this assumption may be close to accurate because the area treated for each retrofit is relatively small compared to the distance between identified retrofit opportunities. In a forested catchment, however, it is unlikely that this assumption would be valid. During the rainy season it is typical for most of a watershed to be saturated and thus hydraulically connected (Walter et al, 2000).

For each potential practice, the contributing roof area, contributing lawn area, and, for rain gardens, area of land taken up by the BMP, were input into the Residential Land Uses column in the model. The same values were input into the BMP characteristics section of the model along with the type of BMP, rain harvesting with a 50% volume reduction for cisterns and bioretention without internal water storage (IWS) for rain gardens. These inputs then trigger the Development Summary of the model to populate with the calculated runoff and nutrient loading values. Annual runoff pre and post development (ft3), total inflow nitrogen (lbs/acre/year), catchment outflow total nitrogen (lbs/acre/year), total inflow phosphorus (lbs/acre/year), and catchment outflow total phosphorus (lbs/acre/year) values were recorded for each practice that was modeled.

To determine the reductions achieved by each potential retrofit, the annual runoff post- development was subtracted from the annual runoff volume pre-development. The outflow nutrient loading values were subtracted from the inflow nutrient loading values, then multiplied by the number of acres treated to yield annual nutrient loading values per practice.

Prioritization Methods: Optimization Tool Development As the City of Durham and Ellerbe Creek Watershed Association have limited resources to implement residential green infrastructure retrofits, it was determined that a decision support tool would be beneficial in defining the highest priority practices based on organizational desires and budgetary constraints. Thus, an optimization model was developed following methodology laid out by Harmon (2012).

Page 19 Ellerbe creek green infrastructure implementation plan All the potential practices and their corresponding stormwater volume and nutrient reductions were input to the model. Cost effectiveness ratios for each practice were calculated based on the stormwater volume reduction and the estimated cost of the retrofit. The cost of each rain garden was determined using the area of the garden and ECWA’s average construction cost per square foot of rain garden, $11/ft2. The costs of 100 and 200 gallon cisterns were determined from listed prices of Agua Fria cisterns ordered from Tijeras with teflon, strapping, pvc fittings, and a drawdown device as well as ECWA’s estimated costs of installation (Tijeras, 2012). Combined, the purchase and installation of a 100 and 200- gallon cisterns was estimated to be $811 and $901 respectively. Cost effectiveness ratios were calculated for each rain garden and cistern opportunity as the cost to implement the practice ($) and the amount of stormwater volume the practice is modeled to reduce annually (ft3). Retrofits with the smallest cost effectiveness ratios yield the greatest volume reductions per dollar it takes to implement them. It should be noted that the costs incorporated into the optimization model are only for implementation and thus do not include future operations and maintenance costs.

Cost effectiveness is rarely the only factor considered when organizations like the ECWA look to implement GI retrofits. Certain areas in an urban landscape may be more ideal for GI based on their proximity to the stream channel or a storm drain. Also, implementing a specific mix of rain gardens and cisterns may be preferable to implementing only one type of retrofit. Constraints for these two preferences were built into the model such that the user can dictate a minimum number of rain gardens or cisterns and a minimum number of retrofits that should be within 60 feet of a stream or a storm drain.

Finally, the maximum budget should be input. Hypothetical values can be used for exploratory analyses and may be helpful when asking for funding from grants, donors, or partner organizations. Inputting an actual maximum budget will allow the user to determine a potential portfolio of practices that meet their constraints and tangible budget limitations. Once all the constraints are set, the optimization can be run using the Excel (2013) Solver Add-in. Solver runs an algorithm that calculates which potential practices should be implemented that maximize the reduction of stormwater volume while also satisfying the user-defined constraints. The optimization model will modify the “Implement” column by coding practices that should be implemented under the given constraints as 1 and all other practices as 0. The site IDs for each practice is in the model so that the practices coded as 1 can be exported to ArcGIS and joined with the spatial data collected from fieldwork. This allows the user to examine the spatial distribution of optimal practices and modify model constraints further or make individual decisions about each practice.

Page 20 Ellerbe creek green infrastructure implementation plan RESULTS

Geospatial Results: Urban Watershed Delineation Tool The Urban Watershed tool allows a user to identify a watershed of interest based on a selected pour point within Ellerbe Creek Watershed. This watershed will then be used to determine if there are any stormwater inflow contributions to that watershed (“stormwater inflow”). Together, the “stormwater inflow” and the natural watershed will be merged to form an “urban watershed.” This tool will be used by Ellerbe Creek Watershed Association to identify where green infrastructure retrofits could be installed to benefit water quality at a point of interest. The user will also receive a geospatial output and an Excel file output containing the parcel ownership information for the properties in the watershed, to allow for mailings to be sent out to those property owners.

The parcel ownership portion of the Urban Watershed tool was also developed as a separate Property Identification Tool so that ECWA can use it to quickly obtain an Excel file containing property ownership information if they already have a shapefile representing an area of interest. Table 3 displays a summary of the outputs created by the tool. Finally, a help document was created and has been given to ECWA to guide future GIS-based green infrastructure analyses (Appendix A).

Table 3. The outputs that are produced by running the Urban Watershed Delineation tool.

Tool Outputs A shapefile that represents the urban watershed: The watershed that contributes to the user selected pour point, as well as any additional “stormwater inflow” to the watershed An Excel file that identifies parcel information for the urban watershed of interest A Shapefile that displays parcel information for the urban watershed of interest

Geospatial Results: Green Infrastructure Retrofit Scoping Tool The result of using the Green Infrastructure Retrofit Scoping tool for Ellerbe Creek Watershed cumulatively identified 4,728 green infrastructure retrofit opportunities (Table 4). Eighteen large parking lots were identified for permeable pavement improvements (Figure 6). 2,086 small parking lots were identified for permeable pavement improvements (Figure 7). Five hundred and eleven individual rooftops were identified for green roof retrofits (Figure 8). Finally, 373 opportunities for green streets with permeable pavement, 760 opportunities for green streets with curb setbacks, 376 opportunities for green

Page 21 Ellerbe creek green infrastructure implementation plan streets with permeable pavement without curb setbacks were identified, and a total of 604 green street bioretention opportunities were identified (Figure 9).

Within the Project Site, 51 green infrastructure opportunities were identified (Table 4). No large parking lots or individual rooftops were identified. This was because the Project Site is comprised of residential properties that do not have large roofs or parking lots within its area. Eleven small parking lots were identified for permeable pavement improvements (Figure 10). Finally, 8 opportunities for green streets with permeable pavement, 14 opportunities for green streets with curb setbacks, and 8 opportunities for green streets with permeable pavement without curb setbacks were identified (Figure 11).

The results must to be validated in the field to determine which recommendations are viable opportunities. Since the green streets analysis was run using assumptions about the widths of roads based on speed limit data, these results need to be confirmed. In the case of individual rooftops, the slope and weight-bearing ability of the roofs need to be assessed. This is an area of future research that should be explored.

Table 4. The results of the Green Infrastructure Retrofit Scoping Tool identified numerous opportunities of each green infrastructure retrofit type for Ellerbe Creek Watershed, with a total of 4,728 opportunities possible. Fifty-one of these opportunities were in the Strayhorn Project Site. Type of Retrofit Number of Opportunities Number of Opportunities Identified in Ellerbe Creek Identified in the Project Site Watershed Large Parking Lots 18 0 Small Parking Lots 2086 11 Individual Rooftops 511 0 Green Streets- Permeable 373 8 Pavement Green Streets- Curb Setback 760 14 Green Streets- Permeable 376 8 Pavement without Setbacks Green Streets- Bioretention 604 10 Total Number of Retrofits 4728 51

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Figure 6: Eighteen large parking lot retrofit opportunities were identified within Ellerbe Creek Watershed.

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Figure 7: Two thousand and eighty six small parking retrofits were identified in Ellerbe Creek Watershed.

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Figure 8: Five hundred and eleven individual rooftop retrofits opportunities were identified in the Ellerbe Creek Watershed.

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Figure 9: A total of 2113 different types of green street retrofits were identified in Ellerbe Creek Watershed.

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Figure 10: Eleven of the small parking lots retrofits that were identified were within the bounds of the Strayhorn Project Site.

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Figure 11: Forty of the different green street retrofit opportunities that were identified were within the bounds of the Strayhorn Project Site.

Page 28 Ellerbe creek green infrastructure implementation plan

Field Results for the Strayhorn Project Site Four hundred and eighty one parcels were assessed within the Project Site. Of these parcels, 63.4%, or 305, were deemed inappropriate for a retrofit. Lack of gutters, steep topography, limited space, and proximity to neighboring parcels were the dominant reasons that parcels were not considered. A limited number of parcels were not considered because they already contained rain gardens or cisterns. In total, 223 retrofits were recommended, including 56 rain gardens, 61 downspout disconnections, and 106 cisterns (Figure 12). Only a single retrofit was recommended per downspout, but multiple retrofits were recommended for some of the parcels. Of the 176 parcels eligible for a retrofit, a single retrofit was recommended for 76.7%, or 135, of the parcels. Within this subset, 69 cisterns, 25 rain gardens, and 41 disconnections were recommended. Thirty-five parcels were considered eligible for two retrofits. Retrofit recommendations were 28 cisterns, 26 rain gardens, and 16 disconnections. Two cisterns were recommended for 6 parcels and 2 rain gardens for 2 parcels; a combination of retrofits was recommended for the remaining 28 parcels. Three retrofits were recommended for 6 parcels; none of the parcels contained three of the same retrofit type.

Page 29 Ellerbe creek green infrastructure implementation plan

Figure 12: Cisterns, rain gardens, and downspout disconnection retrofits identified during fieldwork for the Strayhorn Project Site.

Page 30 Ellerbe creek green infrastructure implementation plan Prioritization Results The model results indicate that if all potential retrofits were implemented, about 67,786 cubic feet or 507,074 gallons of stormwater, 5.1 pounds of total nitrogen, and 0.8 pounds of total phosphorus will be captured at their source annually. This corresponds to average reductions of 827 cubic feet of stormwater, 0.06 pounds of total nitrogen, and 0.01 pounds of total phosphorus per practice. It also corresponds to 0.04 lbs of TN removed per acre per year, and 0.006 TP removed per acre per year. All of the cisterns identified were found to have better stormwater volume reduction capabilities than rain gardens. This is because rainwater harvesting has a volume reduction percentage of 50% in the model while rain gardens are modeled with a volume reduction of 15%. The large difference in stormwater volume reduction potential between the two practices may be due to the highly compacted urban soils and poorly drained clay soils that are characteristic of hydrologic soil group D and the Triassic Basin geology. The effectiveness of rain gardens in Durham are constrained by characteristics of the watershed that do not favor infiltration. However, rain gardens previously implemented by ECWA have not exceeded storage capacity in the growing season, which indicates that the model may be intrinsically underestimating the capacity of rain gardens and soils in Durham. Identified rain garden opportunities average about 289 cubic feet of annual stormwater volume reduction (2,162 gallons), corresponding to reductions in annual TN loading of 0.029 lbs and TP loading of 0.006 lbs. Average annual reductions of rain barrel opportunities identified are 482 cubic feet of stormwater (3,606 gallons), 0.033 lbs of TN, and 0.005 lbs of TP.

Because resources are limited and decisions ultimately depend on the landowner, it cannot be confidently asserted that all of these practices will be implemented. It is thus useful to prioritize practices based on cost effectiveness as well as constraints that meet organizational and project goals. An example scenario was run in the optimization tool with the following constraints: minimum of 5 rain gardens, minimum of 5 practices within a distance of 60 feet from a stream or storm drain, and a maximum budget for implementation of $10,000. Under these conditions the model recommends 14 green infrastructure practices, including 9 cisterns and 5 rain gardens. The total cost of implementing these 14 practices is $9,960.70 and the annual reductions that would be achieved are 10,901 cubic feet of stormwater (81,545 gallons), 0.8 pounds of total nitrogen, and 0.1 pounds of total phosphorus. Identified retrofits were exported into ArcMap to illustrate the spatial distribution and potential for analysis within the neighborhood and watershed context (Appendix D). Refer to Appendix D for a description of the tool and the sample optimization run.

Page 31 Ellerbe creek green infrastructure implementation plan

DISCUSSION There are several assumptions that are inherent in this analysis. First, the JFSLAT assumes that all rainfall events produce runoff (NCDENR, 2011). In forested catchments this would significantly overestimate the amount of runoff that is generated annually, as soil infiltration capacity is high. However, the Project Site encompasses an urban residential area dominated by roofs, roads, sidewalks, and lawns. These surfaces range from impervious to semi-impervious and will therefore generate runoff with even small precipitation depths. Still, there may be events that are small enough to produce no runoff in the Project Site. This may be indicative of a slight overestimate of runoff generation in the model output.

The analysis treats each potential green infrastructure practice as isolated from all other practices and the surrounding watershed. Even in an urban matrix, this assumption does not fully hold true. Shallow subsurface flow and excess overland flow can connect the contributing area of each BMP to adjacent areas- mechanisms that are not accounted for in the modeling methodology. It may be beneficial to utilize a catchment-scale model that calculates the aggregate stormwater, TN, and TP reduction at the catchment outflow. These values could then be compared to the JFSLAT values to determine if the assumption of negligible connectivity is accurate.

Durham, North Carolina is an interesting context for this analysis because the City of Durham is required by NC DEQ to reduce its nutrient impact on Falls Lake. The goal for Ellerbe Creek Watershed is to reduce TN by 7.4 lbs/ac/yr and TP by 0.8 lbs/ac/yr by 2041 (NCDENR, 2011). The reductions achieved by even a full implementation of GI installation in the Strayhorn Project site (5.1 and 0.8 Lbs of TN and TP over 134 acres) would not meet these goals. The regulatory framework for stormwater management is present, but the path forward is still unclear. The City of Durham could invest in stormwater treatment facilities or upgrade current facilities to achieve the reductions mandated in the Falls Lake Nutrient Strategy. These conventional, gray infrastructure approaches are not only enormously costly endeavors, but they are also stop-gap measures rather than solutions at the source. It is recommended that the City spend $56-$60 million in improvements to storm drains and the Durham Wastewater Reclamation Facility to achieve modest reductions in TN and TP, 4% and 19% respectively (Brown and Caldwell, 2010). However, these improvements would reduce fecal coliform inputs into Ellerbe Creek by 59% (Brown and Caldwell, 2010). Constructing all 56 rain gardens and 107 cisterns that were identified in the Strayhorn project site would

Page 32 Ellerbe creek green infrastructure implementation plan cost around $124,000. While the aggregate nutrient reductions of the potential rain gardens and cisterns is small (0.04 lbs of TN removed per acre per year and 0.006 lbs TP removed per acre per year), the total cost of implementation is also small. Implementing GI has additional ancillary benefits that include helping to restore the natural hydrology of the system as well as engaging the local community in stormwater issues and empowering them to be part of the solution. Consultants have determined that the gray infrastructure upgrades are the most cost effective, so pairing this type of investment with comparably low-cost, dispersed GI retrofits may be an effective first step forward towards restoring natural hydrology and water quality to Ellerbe Creek (Brown and Caldwell, 2010). An integrated strategy that involves gray and green infrastructure can capitalize on the benefits of both approaches, potentially resulting in high fecal coliform reductions, paired centralized and decentralized nutrient removal practices, ancillary community benefits, and a holistic and resilient stormwater management system.

Recently, the shift towards a mixture of green and gray infrastructure improvements has gained traction in the sphere of local stormwater mitigation, as employing both large and small-scale stormwater treatment becomes a more attractive strategy. The current research on the identification and evaluation of potential sites for green infrastructure is sparse. This report is intended to fill this gap in the literature by providing a methodology for local governments or non-profit organizations like ECWA to begin analyzing the potential of dispersed green infrastructure retrofits in their watershed that can supplement centralized treatment. The Urban Stormwater Delineation tool can help organizations determine the ownership of properties within the contributing area of a polluted stream. Not only does this define the scope of the necessary solution, it also generates an Excel file with the contact information of relevant parties where outreach can begin. The Green Infrastructure Retrofit Scoping Tool proves to be an effective method to identify large-scale commercial green infrastructure opportunities without time-intensive site visits and field work. The identified sites can then be ground-truthed with more focused field work. The field methods used in this project can be adopted and used in any residential area to pin-point potential sites for smaller scale practices on residential lots. Combined, these processes can save organizations time and resources, which makes developing a plan for green infrastructure implementation a feasible endeavor, even for organizations without a large capacity.

Furthermore, it is valuable to have the ability to communicate the potential positive impacts of a GI implementation plan to stakeholders and donors. The JFSLAT can be used to model stormwater, total nitrogen, and total phosphorus reductions that identified projects will provide. The tool is developed for

Page 33 Ellerbe creek green infrastructure implementation plan the state of North Carolina, so it is recommended that either local or nation-wide models are used when undertaking similar analyses in different states. The results of JFSLAT also allow for more technical analyses comparing the efficacy of conventional stormwater treatment options and green infrastructure options. As in this analysis, the modeled reductions can subsequently be used to develop a prioritization scheme. With the increasing austerity of non-profit and municipal budgets, identifying the highest priority retrofits is essential to financial and resource efficiency. The optimization tool developed for this project highlights the most cost effective practices and permits the user to indicate several constraints based on their own desired outcomes. Ultimately, these methods and tools are meant to aid future GI projects, such that small organizations can efficiently scope, identify, and prioritize green infrastructure opportunities that promote their watershed restoration goals.

Future Directions The Jordan/Falls Lake Stormwater Nutrient Load Accounting Tool version 3.0 is in development and will include the ability to model the nutrient reductions associated with downspout disconnections. Alternatively, it could be beneficial to explore other models that ECWA can use to calculate the stormwater and nutrient reductions associated with multiple green infrastructure project types. Finally, in order to estimate the percent reductions associated with these projects, a baseline study that computes the annual phosphorus and nitrogen contained in Ellerbe Creek Watershed’s runoff would need to be completed. Furthermore, we hope that a monitoring program can be created to enlist volunteers to measure water quality improvements associated with the implementation of green infrastructure practices. This could be achieved by monitoring water quality after storm events or by measuring stream stage and discharge to monitor stormwater volumes. Not only would a volunteer-based monitoring program allow for a better understanding of the improvements associated with green infrastructure, it would also promote community involvement and education about these efforts.

Finally, the results of Green’s Green Infrastructure Retrofit Scoping Tool (2015) identified numerous opportunities for large-scale commercial and industrial green infrastructure projects. This avenue is an excellent opportunity for future collaboration between ECWA and private and public partners within the community.

Page 34 Ellerbe creek green infrastructure implementation plan CONCLUSIONS Ellerbe Creek is a severely degraded urban stream located in Durham, North Carolina. The high percentage of impervious surface within its watershed has contributed to altered hydrology and increased inputs of nitrogen, phosphorus, and other forms of aquatic pollution. Because Ellerbe Creek is a tributary to Falls Lake, a drinking water reservoir, the City of Durham has been tasked with reducing nutrient loading to the creek. Ellerbe Creek Watershed Association has done extensive research into the possibility of controlling and treating the volume and pollutant load of stormwater runoff using dispersed green infrastructure technologies, which are often more ecologically beneficial than traditional gray infrastructure projects. They also provide ancillary benefits that align with ECWA’s community engagement and well- being goals. The objective of this project was to expand upon a pilot study completed by ECWA in 2014 by identifying additional opportunities for retrofits within Ellerbe Creek Watershed. The project was completed using a three-pronged linear approach: geospatial analysis, field data collection, and scenario planning using the identified retrofit opportunities.

A desktop analysis was first completed for the entire watershed using geospatial techniques. This GIS analysis identified large scale and commercial retrofit opportunities including large and small parking lots, green roofs, and green streets. An Urban Watershed Delineation tool was also created to aid ECWA in identifying drainage areas and associated parcel data for any user-selected point in the watershed. A field methodology was developed to evaluate retrofits within the largely residential Strayhorn Project Site that geospatial analysis was unable to detect. All parcels within this 134-acre intensification area were evaluated by field crews for rain garden, downspout disconnection, and cistern retrofits; a total of 223 opportunities were discovered. The stormwater improvement capabilities of each rain garden and cistern 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 allow ECWA to engage in scenario planning using the field data and model results. This tool is flexible in that it allows the user to define various constraints, such as total budget, minimum number of a certain retrofit, or proximity to the stream, thus enabling ECWA to use it with this data and that of other sub-catchments.

In conclusion, the results of this project have equipped ECWA with the data and tools they need to implement both residential and commercial retrofits. At the time of completion of this project, ECWA had already begun contacting landowners to assess interest in the implementation of the residential retrofits

Page 35 Ellerbe creek green infrastructure implementation plan identified by the field data collection. The geospatial results are available to ECWA to implement larger commercial and industrial GI projects as funds and opportunities for collaboration become available. In addition, tools including the GIS-based Urban Watershed Delineator and optimization model, will be utilized by ECWA as they begin the process of expanding retrofit implementation from the Project Site into the larger Ellerbe Creek Watershed. While each retrofit by itself may not impact water quality in a discernable manner, implementation of a suite of dispersed projects has the potential to improve the water quality in Ellerbe Creek, as well as provide ancillary benefits such was increased community awareness of stormwater issues and solutions in Durham.

Page 36 Ellerbe creek green infrastructure implementation plan ACKNOWLEDGEMENTS We would like to thank our advisors Dr. Julie DeMeester and Dr. James Heffernan for their guidance and expertise during our project process. Additionally, we are grateful for our client at Ellerbe Creek Watershed Association, Chris Dreps, and Robert Meehan, who assisted with our fieldwork. Thank you to Benjamin Green, who allowed us to utilize his Green Infrastructure Retrofit Scoping Tool for this project. Thank you to Lars Hanson and Mike Dupree for fielding questions throughout the modeling process. Finally, thank you to our professors at Duke University who imparted on us the skills and knowledge to be able to execute this project.

Page 37 Ellerbe creek green infrastructure implementation plan REFERENCES Avenza Systems, Inc. (2016). PDF Maps: Version 2.7.1 for iOS. Toronto, Canada.

Brown and Caldwell. (2010). Ellerbe Creek Watershed Management Improvement Plan. Prepared for City of Durham.

Center for Watershed Protection. (2007). Urban Stormwater Retrofit Practices Appendices.

City and County of Durham, NC. (2015). GIS Data Source: Street Centerlines. Provided by ECWA; Can be accessed from .

City of Durham. (2011). City of Durham Stormwater Management Program Plan. .

Dunne, T. & Leopold, L. (1978). Water in Environmental Planning. New York, NY: W. H. Freeman and Company.

Duke University Libraries. (2010). GIS Data Source: Storm Water Nodes and Storm Water Pipes. Provided by ECWA; Can be accessed from .

Durham County Building Footprints. (2012). GIS Data Source. Provided by ECWA; Can be accessed from .

Dreps, C., Hanson, L., and Raabe, P., (2014). Ellerbe Creek Green Infrastructure Partnership Technical Report: Ellerbe Creek Green Infrastructure Partnership.

ECWA. (2012). GIS Data Source: Ultimate open space components (Triangle J Council of Governments, Parks, City, and Government Owned).

ECWA. (2015). GIS Data Source: NC Durham Impervious Area.

ECWA Vision Statement. Ellerbe Creek Watershed Association Vision Statement and Our Work. Can be accessed from .

EPA. (2014) “Enhancing Sustainable Communities with Green Infrastructure.” (EPA Publication No. 100-R- 14-006). Washington, DC: Office of Sustainable Communities, Smart Growth Program.

EPA. (2014). “Green Infrastructure.” Washington, DC: Water. Retrieved from http://water.epa.gov/infrastructure/greeninfrastructure/index.cfm#tabs-2.

ESRI. (2015). ArcGis Desktop: Release 10.3. Redlands, CA: Environmental Systems Research Institute.

Franzetti, S. (2005). Background and History of Stormwater Regulations. Sponsored by Lorman Education Services: Oak Brook, IL.

Google. (2015). Google Forms. Mountain View, CA.

Green, B. (2015). “Impacts of Green Infrastructure implementation within the Neuse River Basin.” Retrieved from http://dukespace.lib.duke.edu/dspace/handle/10161/9672.

Page 38 Ellerbe creek green infrastructure implementation plan Holman-Dodds, J., Bradley, A., & Potter, K. (2003). “Evaluation of Hydrologic Benefits of Infiltration Based Urban Storm Water Management.” JAWRA 39(1): 205-215.

Lopes, T., Fossum, K., Phillips, J., & Monical, J. (1995). “Statistical Summary of Selected Physical Chemical, and Microbial Characteristics and Estimates of Constituent Loads in Urban Stormwater, Maricopa County, Arizona.” U.S. Geological Survey: Water-Resources Investigations Report 94-4240.

Microsoft Corporation. (2010). Microsoft Excel for Mac 2011: version 14.6.2.

NCDENR. (2011). “Falls Nutrient Strategy.” Raleigh, NC.

NCDENR. (2011). Jordan/Falls Lake Stormwater Load Accounting Tool (Version 1.0) User’s Manual. Developed by NC State University Biological and Agricultural Engineering Department for the NC Department of Environment and Natural Resources. Revised January 31. Available on the internet at: http://portal.ncdenr.org/c/document_library/get_file?uuid=c54894f6-4d95-43d3-bdc5- c1c694253b24&groupId=38364

NCDENR. (2013) “Summary of Findings and Recommendations for the Ellerbe Creek Local Watershed Plan.” Raleigh, NC: Ecosystem Enhancement Program.

North Carolina Flood Risk Information System. (2007). LiDAR DEM 20. Accessed 10/1/2015 at .

NC One Map. Durham parcels. (2015). Accessed 9/20/2015 at .

NC Water Quality Division. (2010) “NC 2010 Integrated Report Categories 4 and 5 Impaired Waters.” Raleigh, NC.

NC Water Quality Division. (2013). NPDES Permit NCS000249. City of Durham.

Murakami, M., Sato, N., Anegawa, A., Nakada, N., Harada, A., Komatsu, T., Takada, H., Tanaka, H., Ono, Y., & Furumaai, H. (2008). “Multiple evaluations of the removal of pollutants in road runoff by soil infiltration.” Water Research 42: 2745-2755.

Python Software Foundation. (2015). Python.org.

Schueler, T., Hirschman, D., Novotney, M., and Zielinski, J., (2007). Manual 3: Urban Stormwater Retrofit Practices: Center for Watershed Protection.

Tijeras Rain Barrels. (2012). Agua Fria Series. Retrieved from https://www.tijerasrainbarrels.com/rb- agua.html.

Walsh, C. J., Roy, A. H., Feminella, J. W., Cottingham, P. D., Groffman, P. M., & Morgan, R. P. (2005). “The urban stream syndrome: current knowledge and the search for a cure.” Journal of the North American Benthological Society 24(3): 706.

Page 39 Ellerbe creek green infrastructure implementation plan Walter, M., Walter, M., Brooks, E., Steenhuis, T., Boll, J., & Weiler, K. (2000). “Hydrologically Sensitive Areas: Variable Source Area Hydrology Implications for Water Quality Risk Assessment.” Journal of Soil and Water Conservation 3: 277-284.

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APPENDIX A: URBAN WATERSHED DELINEATION USER MANUAL

ELLERBE CREEK URBAN WATERSHED DELINEATION TOOL

Bethany Williams

[email protected]

Page 41 Ellerbe creek green infrastructure implementation plan SUMMARY

Purpose of the Tool

The Urban Watershed Delineation tool allows a user to identify a watershed of interest based on a selected pour point within Ellerbe Creek Watershed. This point is user defined and is called a “pour point.” This means that the watershed is delineated based on the area of the land that eventually drains to this point. A snap distance of 30 was used in this tool, meaning that the tool will adjust the location of the pour point to the cell with the most flow accumulation within the closest 30 cells to the user-defined pour point. These cells were 20 by 20 feet in size. This snap distance of 30 was determined to work well with the data available for Ellerbe Creek Watershed, and is therefore recommended for use in this tool so that the user does not have to click on the map in the perfect location for the tool to be able to run. The tool will adjust the location of this point for optimal results.

This watershed will then be used to determine if there are any stormwater inflows contributions to that watershed (“stormwater inflow”). Together, the “stormwater inflow” and the natural subwatershed will be merged to form an “urban watershed.” This tool will be used by Ellerbe Creek Watershed Association (ECWA) to identify where green infrastructure should be put to benefit water quality at a point of interest. The user will also receive an Excel file output containing the parcel ownership information for the properties in that watershed, to allow for mailings to be sent out to those property owners.

The parcel ownership portion of the Urban Watershed Delineation tool was developed into a separate Property Identification Tool so that ECWA can use it to quickly get an Excel file containing property ownership information if they already have a shapefile of an area that they are interested in. Instructions for this tool can be found under Step 5 of the Urban Watershed Delineation Tool tutorial, below.

Data Inputs

• 20 ft. resolution DEM of Ellerbe Creek Watershed (North Carolina Flood Risk Information System, 2007) • 60 ft. buffer of all stormwater pipes and inflow points in Ellerbe Creek Watershed (Duke University Libraries, 2010) • A flow accumulation raster derived from the DEM • A raster showing where flow accumulation is greater than 500 contributing pixels (to direct the user on areas to click on the map) • County of Durham property ownership data (NC One Map, 2015)

User Inputs

• The user must click on the map to select the pour point they are interested in; a default location of the pour point of the Strayhorn Project Site can be used • Specify the snap distance for the user selected pour point. This adjusts the location of the pour point to make sure it fits the flow accumulation paths; a value of 30 is suggested

Page 42 Ellerbe creek green infrastructure implementation plan • Name for the urban watershed shapefile (located within the Data folder) • Name for the parcel information shapefile and Exel file (located within the Data folder)

Tool Outputs

• A shapefile that represents the urban watershed: The watershed that contributes to the user selected pour point, as well as any additional “stormwater inflow” to the watershed • An Excel file that identifies parcel information for the urban watershed of interest • A Shapefile that displays parcel information for the urban watershed of interest

INSTRUCTIONS AND EXAMPLE WORKFLOW

Step 1:

The display on the Urban_Watershed_Tool.mxd file shows the flow accumulation network, User Selectable Flow Paths. Areas that are shown in colors ranging from red to blue are areas that can be clicked on as potential pour points for the urban watershed tool. The yellow star represents an example pour point, which is the Strayhorn Project Site pour point. This is also the cursor that will be used to click on the map. A basemap is displayed to aid the user in identifying areas within Ellerbe Creek Watershed. The user can move around to any area within Ellerbe Creek Watershed that they are interested in, which has been outlined on the map in black.

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Step 2:

Open the UrbanWatershedDelineator tool from the UrbanWatersheds Toolbox. The user should now use the yellow star-shaped cursor to click a point on the flow accumulation network that they are interested in. This will be used as the pour point for the tool; the outputs of the tool will show the watershed that contributes to this point.

Page 44 Ellerbe creek green infrastructure implementation plan Step 3:

Specify a threshold distance used for the pour point the user has clicked on. This will adjust the location of the user selected pour point to ensure that the point is located on a flow path. This will allow the tool to work best. A suggested value is 30. At this time, also specify the desired name for the urban watershed shapefile, the property identification shapefile, and the property identification Excel file. All outputs will go to the Data folder.

Step 4:

The tool will now run and produce several files behind the scenes to arrive at the urban watershed of interested that contributes to the user-selected pour point. The final output of interest will be the urban watershed shapefile, which shows the combined contribution of stormwater and natural flow to the user selected pour point (located in the Data folder); the name will be based on the user’s specifications.

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The steps that this portion of the tool follow are:

1) Snap the pour point to the flow accumulation raster using the user specified threshold distance 2) Delineate the watershed based on the flow direction file 3) Convert this watershed to a shapefile and use the select by location feature to determine if any stormwater inflows contribute to this area 4) Merge the stormwater inflow network and the delineated watershed to create the urban watershed 5) Use select by location to determine the ownership information for properties that fall partly or entirely within the urban watershed 6) Create a shapefile and Excel file of these properties

Step 5:

The final outputs of interest also include the property identification shapefile, which contains information on the parcels that fall partly or entirely within the urban watershed. This file is located in the Data folder, and the name will be based on the user’s specifications. Additionally, the tool will produce an Excel file of this property information, for which the name will be based on the user’s specifications. Note: The Property Identification Tool follows the same workflow as this portion of the Urban Watershed Delineation Tool.

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DATA SOURCES AND PRE-PROCESSING

Sources:

Duke University Libraries. (2010). GIS Data Source: Storm Water Nodes and Storm Water Pipes. Provided by ECWA; Can be accessed from .

North Carolina Flood Risk Information System. (2007). LiDAR DEM 20. Accessed 10/1/2015 at .

NC One Map. Durham parcels. (2015). Accessed 9/20/2015 at .

Data Pre-Processing:

To prepare data for this tool, the appropriate Digital Elevation Model (DEM) imagery was downloaded at a 20 ft. resolution for Ellerbe Creek Watershed (North Carolina Flood Risk Information System, 2007). This data was converted from asc format to a raster and then was merged and clipped to the shape of Ellerbe Creek Watershed. Finally, this DEM was filled, and flow accumulation and flow direction were computed.

Next, a 60 ft. buffer around stormwater inflow points and pipes for the entire Ellerbe Creek Watershed was created (Duke University Libraries, 2010). This is used to determine if there are urban stormwater contributions to the natural watershed.

Page 47 Ellerbe creek green infrastructure implementation plan APPENDIX B: GREEN INFRASTRUCTURE RETROFIT SCOPING TOOL METHODS

The follow adaptations from Green’s (2015) original Green Infrastructure Retrofit Scoping Tool were made to accommodate differences in datasets available for the Ellerbe Creek Watershed.

Large Parking Lots Method used in the Green Infrastructure Retrofit Scoping Tool: “Used ‘Parking’ layer, selected from features that were > 5ac and were within 50m of public open space, which would allow for reasonable construction conveyance to offsite detention/infiltration practices (Green, 2015).”

Method used in Ellerbe Creek Analysis: No dataset for parking lots exists for Durham, so an impervious area layer from the City of Durham was used; ArcGIS was used to remove any areas that represented building footprints (ECWA, 2015). This data was then used as the ‘Parking’ layer for the Green Infrastructure Retrofit Scoping tool. Features within this dataset that were greater than 5 acres were selected and were subsequently selected for a retrofit opportunity if they were within 50 meters of public open space. This data layer for open space was provided by ECWA and included data from the Triangle J Council of Governments, ECWA’s preserves, and all city and government owned parcels (ECWA, 2012). The original tool has restrictions on the type of owner of the parking lot, which were removed from this analysis in order to identify as many opportunities as possible.

Small Parking Lots Method used in the Green Infrastructure Retrofit Scoping Tool: “Used ‘Parking’ layer, selected from features that were less than 5 acres (Green, 2015).”

Method used in Ellerbe Creek Analysis: The same data layer for large parking lots was used for the small parking lots tool. Features within this dataset that were less than 5 acres were selected. To remove driveways that were inadvertently included in the results, these results were further narrowed down to include only those that were not on residential parcels.

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Individual Rooftops Method used in the Green Infrastructure Retrofit Scoping Tool: “Superimpose property ownership layers with aerial photos or impervious land cover data to locate large (>0.25 acres) municipal, institutional, commercial or industrial buildings that may be assessed for demonstration rooftop retrofits or look for clusters of building permit data that indicates areas experiencing active redevelopment (Dreps et al, 2014).”

Method used in Ellerbe Creek Analysis: A data layer of the building footprints within Ellerbe Creek Watershed was available from Durham County (2012). This layer was used to select rooftops that were greater than 0.25 acres.

Green Streets Method used in the Green Infrastructure Retrofit Scoping Tool: “Streets were selected based upon the user’s desired maximum speed limit for roads upon which they would like to implement three separate features: permeable pavement within parking lanes, in-street bioretention, and curb setbacks. The permeable pavement component creates a roadway buffer clipped within the width of a parking lane on both sides of a street of standard measure in Raleigh, NC. Curb setbacks also perform a buffer, but it is limited to the corners which fit the speed limit criteria. Finally bioretention looks to identify drainage grates so that swales and other infiltration devices could be designed with available drainage to decrease the likelihood of retrofit failure (Green, 2015).”

Method used in Ellerbe Creek Analysis: The Large Parking Lots Green Infrastructure Retrofit Scoping tool was used as it was designed without modification. The speed limit used for the three separate features was set at 35 miles per hour, since this is the typical speed limit of many residential areas in the watershed (City and County of Durham, NC, 2015). It was important to ensure that the output included only residential roads that would be suitable for green street retrofits. Furthermore, the data for the bioretention opportunities came from identifying inflow points from stormwater data features (Duke University Libraries, 2010).

Page 49 Ellerbe creek green infrastructure implementation plan APPENDIX C: RESIDENTIAL RETROFIT FIELD DATA COLLECTION FORM

2/21/2016 Residential Retrofit Form

Residential Retrofit Form To be used to identify green infrastructure retrofits on residential parcels.

downspout disconnections, rain gardens and cisterns

1. Site ID Each parcel is labeled with a unique Site ID, see PDF Maps

2. Latitude

3. Longitude

4. Site Address(es)

5. Field Team Members Check all that apply.

Amanda Close Christina Davis Bethany Williams Chris Dreps Robert Meehan

https://docs.google.com/forms/d/1WgECO9Y2R5vBj_Sd-t7GTY9FMWtfVMCLtDVuBX_aoMs/edit 1/8

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2/21/2016 Residential Retrofit Form 6. Property Type Mark only one oval.

Single Family Residential Multifamily Residential Apartment Complex Commercial Industrial

Other:

7. Occupation Status Mark only one oval.

Owner Occupied Rental Property Unoccupied Unknown

8. Number of Downspouts How many downspouts are at the site?

9. Disconnected Downspouts How many of the downspouts are disconnected?

10. Existing BMP Are there existing BMPs? If yes, select which ones Mark only one oval.

No Raingarden Cistern

Other:

11. Recommended Retrofits What retrofits would you recommend for this site? Check all that apply.

Downspout disconnection(s) Rain garden(s) Cistern(s)

https://docs.google.com/forms/d/1WgECO9Y2R5vBj_Sd-t7GTY9FMWtfVMCLtDVuBX_aoMs/edit 2/8

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2/21/2016 Residential Retrofit Form 12. Next Page: Click the appropriate retrofit type to navigate to one of the following pages Mark only one oval.

Downspout Disconnection Skip to question 13. Rain Garden Retrofit Skip to question 16. Cistern Retrofit Skip to question 30.

Downspout Disconnection Note: downspout disconnection retrofits should only be considered if a rain garden or cistern is not feasible.

13. Proposed Disconnections How many downspouts have been identified to be disconnected?

14. Downspout Disconnection Notes Make other notes here.

15. Navigate to Next Page Mark only one oval.

Rain Garden Retrofit Skip to question 16. Cistern Retrofit Skip to question 30. General Site Considerations Skip to question 40.

Skip to question 40. Rain Garden Retrofit Note: For a property to be eligible for a rain garden, there must be an appropriately sized space located 10+ feet away and downslope of the building

16. Roof Drainage Area 1 What is the approximate roof drainage/collection area to the site? (ft2)

https://docs.google.com/forms/d/1WgECO9Y2R5vBj_Sd-t7GTY9FMWtfVMCLtDVuBX_aoMs/edit 3/8

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2/21/2016 Residential Retrofit Form 17. Pervious Drainage Area 1 What is the approximate pervious drainage area to the site? (ft2)

18. Rain Garden Area 1 What is the total area needed for a rain garden? (ft2) [garden area = 10% of roof area + 1% of pervious area]

19. Roof Drainage Area 2 What is the approximate roof drainage/collection area to the site? (ft2)

20. Pervious Drainage Area 2 What is the approximate pervious drainage area to the site? (ft2)

21. Rain Garden Area 2 What is the total area needed for a rain garden? (ft2) [garden area = 10% of roof area + 1% of pervious area]

22. Roof Drainage Area 3 What is the approximate roof drainage/collection area to the site? (ft2)

23. Pervious Drainage Area 3 What is the approximate pervious drainage area to the site? (ft2)

24. Rain Garden Area 3 What is the total area needed for a rain garden? (ft2) [garden area = 10% of roof area + 1% of pervious area]

https://docs.google.com/forms/d/1WgECO9Y2R5vBj_Sd-t7GTY9FMWtfVMCLtDVuBX_aoMs/edit 4/8

Page 53 Ellerbe creek green infrastructure implementation plan

2/21/2016 Residential Retrofit Form 25. Roof Drainage Area 4 What is the approximate roof drainage/collection area to the site? (ft2)

26. Pervious Drainage Area 4 What is the approximate pervious drainage area to the site? (ft2)

27. Rain Garden Area 4 What is the total area needed for a rain garden? (ft2) [garden area = 10% of roof area + 1% of pervious area]

28. Rain Garden Retrofit Notes Make other notes here. [Include if proposed garden depth will differ from 10cm standard]

29. Navigate to Next Page Mark only one oval.

Downspout Disconnection Skip to question 13. Cistern Retrofit Skip to question 30. General Site Considerations Skip to question 40.

Skip to question 40. Cistern Retrofit Note: For site to be appropriate for a cistern there must be an area for water to naturally drain away from the house in case of an overflow event.

30. Roof Area 1 What is the approximate collection area? (ft2)

https://docs.google.com/forms/d/1WgECO9Y2R5vBj_Sd-t7GTY9FMWtfVMCLtDVuBX_aoMs/edit 5/8

Page 54 Ellerbe creek green infrastructure implementation plan

2/21/2016 Residential Retrofit Form 31. Cistern Size 1 What size cistern is appropriate for the site? Mark only one oval.

100 gallons [3.5 ft high, 24 inch diameter] 200 gallons [3.5 ft hight, 38 inch diameter] 360 gallons [3.5 ft high, 48 inch diameter]

32. Roof Area 2 What is the approximate collection area? (ft2)

33. Cistern Size 2 What size cistern is appropriate for the site? Mark only one oval.

100 gallons [3.5 ft high, 24 inch diameter] 200 gallons [3.5 ft hight, 38 inch diameter] 360 gallons [3.5 ft high, 48 inch diameter]

34. Roof Area 3 What is the approximate collection area? (ft2)

35. Cistern Size 3 What size cistern is appropriate for the site? Mark only one oval.

100 gallons [3.5 ft high, 24 inch diameter] 200 gallons [3.5 ft hight, 38 inch diameter] 360 gallons [3.5 ft high, 48 inch diameter]

36. Roof Area 4 What is the approximate collection area? (ft2)

37. Cistern Size 4 What size cistern is appropriate for the site? Mark only one oval.

100 gallons [3.5 ft high, 24 inch diameter] 200 gallons [3.5 ft hight, 38 inch diameter] 360 gallons [3.5 ft high, 48 inch diameter]

https://docs.google.com/forms/d/1WgECO9Y2R5vBj_Sd-t7GTY9FMWtfVMCLtDVuBX_aoMs/edit 6/8

Page 55 Ellerbe creek green infrastructure implementation plan

2/21/2016 Residential Retrofit Form 38. Cistern Retrofit Notes Make other notes here.

39. Navigate to Next Page Mark only one oval.

Downspout Disconnection Skip to question 13. Rain Garden Retrofit Skip to question 16. General Site Considerations Skip to question 40.

Skip to question 40. General Site Conditions and Constraints

40. Conflicts with Existing Utilities Mark only one oval per row.

Yes Possible Sewer Water Gas Cable/Data Electric Street Lights/Overhead Wires

41. General Property Maintenance Mark only one oval.

1 2 3

Property very neglected Well maintained property

42. Roof and Gutter Condition Mark only one oval.

1 2 3

Roof in poor condition, gutters completely Well clogged maintained

https://docs.google.com/forms/d/1WgECO9Y2R5vBj_Sd-t7GTY9FMWtfVMCLtDVuBX_aoMs/edit 7/8

Page 56 Ellerbe creek green infrastructure implementation plan

2/21/2016 Residential Retrofit Form 43. Gardening Evidence Is there an established garden on site? Mark only one oval.

Yes No

44. Photos If photos were taken, please note which device and the image numbers

45. Overall Site Observations and Considerations

Powered by

https://docs.google.com/forms/d/1WgECO9Y2R5vBj_Sd-t7GTY9FMWtfVMCLtDVuBX_aoMs/edit 8/8

Page 57 Ellerbe creek green infrastructure implementation plan APPENDIX D: RESIDENTIAL RETROFIT OPTIMIZATION TOOL

Anatomy of the Tool The optimization tool is a Microsoft Excel based model that requires the Solver Add-in to run. Once the tool is open in Excel, the Solver Add-in can be activated via the commands: File>Options>Add- Ins>Manage Excel Add-ins, Go…>Check the Solver Add-in box>OK.

The following is a description of the anatomy of the optimization tool spreadsheet. The image below is intended to be a reference for these descriptions.

Data Data for all rain gardens and cisterns identified in the Strayhorn Project Site has been input into the Excel sheet. The RG and Cistern columns code whether the retrofit is a rain garden or a cistern. For example, a rain garden would receive a 1 in the “RG” column and a 0 in the “Cistern” column. If the retrofit is a cistern, the 0 and 1 would be in opposite columns. The “Implement column”, highlighted in green, is what the Solver Add-in will manipulate while running the optimization equation. This column will start as 0 and will change to 1 for each retrofit that should be implemented under the user-defined constraints. The retrofits that receive a 1 are the retrofits that the model recommends to be implemented. The “Within stream or storm drain buffer” column codes whether the retrofit is within 60 feet of a stream or storm drain. This was determined by running the buffer tool on the stream network and storm drains in the Strayhorn Project Site and intersecting this buffer with the point data for identified retrofit opportunities. The “Cost” column indicates how much each retrofit would cost to construct (not including ongoing operations and maintenance costs). For cisterns this is based on the size of the cistern and cost data provided by ECWA. For rain gardens, average cost and average size were determined from ECWA’s

Page 58 Ellerbe creek green infrastructure implementation plan organizational records and used to extrapolate an average construction cost per square foot of rain garden of $11. This cost is multiplied by the rain garden size that was estimated in the field to determine the total construction cost of each different rain garden opportunity. The following three columns are results from JFSLAT, stormwater volume and nutrient reductions. The “$/volume” column is the cost effectiveness ratio for each retrofit and was calculated by dividing the cost of the retrofit by the volume of stormwater that it reduces. This is the optimization equation uses these ratios to identify the most effective projects to implement. The final two columns indicate the cumulative stormwater volume reduction and cumulative cost that implementing the projects would provide. These can be thought of as marginal benefits of implementing the next most cost effective project.

Constraints In the top left of the Excel sheet is the “Constraints” section highlighted in light green. This is where users can input constraints based on organizational goals, budget limitations, or spatial priorities. The first two constraints “Cistern” and “Rain Garden” indicate the minimum number of cisterns or rain gardens that the user would like the tool to output. If 5 rain barrels are donated from the local hardware store or if a grant requires 10 rain gardens to be built with the funding, these are useful constraints to enter. The user should modify cells E5 and E6 with any desired minimum number of each practice. The next constraint is “Retrofits w/in stream or storm drain buffer”. Again, this refers to all retrofits in the Strayhorn site that have been identified through ArcGIS to be within 60 feet of a stream or storm drain inflow. This proximity and direct connection to a stream makes these areas especially valuable to retrofit, so stormwater does not reach the stream without natural infiltration and treatment. The user should manipulate cell E7 with the desired number of retrofits that fall within this zone. GIS identified 21 retrofits that meet this criteria, so entering numbers larger than 21 will result in an error. Finally, the “Max budget” cell (E9) allows the user to enter in a total cost for implementing the practices. If an organization receives grant funding or donations for GI implementation, they will be able to run the model with this real budgetary constraint.

Objective Under the “Constraints” section is the “Objective” section. The objective is what the Solver Add-in uses an optimization equation to maximize. It is currently set to cell D12 or the total reduction in cubic feet of flow that all the recommended retrofits provide. This cell is highlighted in darker orange. This number is determined by multiplying the binary “Implement” column by the “Annual SW Volume Reduction” column which results in the total stormwater volume reduced by only the retrofits that are recommended to be implemented. The objective can also be changed to maximize the reduction in total nitrogen or total phosphorus which are directly below the current objective cell.

Example Tool Run 1. The following constraints were input: Minimum rain gardens (cell D6): 5 Minimum retrofits within a stream or storm drain buffer (cell D7): 5 Maximum budget (cell D9): $10,000

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2. The Solver Add-in was opened: Data>Analysis>Solver. If the Solver tool does not appear in the Data tab, refer to the beginning of Appendix D to activate the Add-in. The Solver Parameters are already input into the tool. If the default parameter setting are not saved in the Solver window, they can be loaded in by clicking “Load/Save”, selecting cells N4-N12, then clicking “Load.” This process can also be used to reset the parameters to the defaults after any modifications. The objective is set to maximize cell D12 or the reduction in flow, but can be changed to D13 or D14 for reduction in total nitrogen or total phosphorus. The variable cells are set to the “Implement” column (E17-E179) which means that Solver can manipulate the values in this column to solve maximize the value in the objective cell. The first three constraints are set such that the Actual values for cisterns, rain gardens, and retrofits within the stream and storm drain buffer are equal to or greater than the user defined minimum values. The fourth constraint indicates that the actual expenditure for all the recommended retrofits (cell C9) cannot exceed the user defined maximum budget (cell D9). The last constraint tells Solver that the “Implement” column must be binary, meaning it can only change these values to a 0 or a 1. This makes sense because it is impossible to construct the exact same rain garden more than one time- you either construct it (1) or you do not construct it (0).

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3. Ensure the Solving Method is “Simplex LP” and click Solve. A “Solver Results” window will appear. Check “Keep Solver results” then click OK. 4. The spreadsheet has now been modified with the results of the optimization run. The retrofits that Solver recommends to be implemented now are coded as 1 in the “Implement” column. The actual expenditure if all the recommended retrofits are constructed has been calculated as well as the total reductions in stormwater volume and nutrients (in the Objective section of the spreadsheet).

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5. The “Implement” column can be sorted by value and all retrofits coded as 1 can be exported and joined to the GIS shapefile with all retrofits based on the value in the “Site ID” column. The recommended retrofits can then be analyzed spatially in the context of the subwatershed as depicted in the sample output below. 6. To reset the values, enter 0 into every cell in the “Implement” column. This can be done quickly by entering a 0 in the first cell then pulling down the corner of the cell to the bottom of the data column.

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Potential Uses This optimization model was developed to provide ECWA with specific recommendations based on their organizational constraints. It became clear that instead of generating a single output with specific recommendations, it is more valuable to the organization to have the ability to test scenarios and explore the field and modeled data from this analysis in a comprehensive, goal-oriented fashion. Because of this, it is important to specify that the user-defined constraints do not have to be based-on real situations, but can be exploratory values to aid understanding and decision-making.

Furthermore, it is difficult for organizations to develop a whole subwatershed or even whole neighborhood green infrastructure retrofit plan especially when implementation almost solely rests on how amenable the landowner is to retrofitting their property. So, the tool can also be used as a communication aid. The benefits of projects that have already been implemented or are in the process of being implemented can be easily calculated with the model (change the value in the “Implement” column from a 0 to a 1 for each project and results will be calculated in the objective section). Also, because the modeled data is correlated to each parcel, it can be used to communicate to landowners the potential benefits that implementing a retrofit on their property would have in the watershed, making the implications of their decisions quantifiable and tangible.

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