WATERSHED APPROACH TO RECOVERING URBAN STREAMS: MONTICELLO CREEK CASE STUDY USING SUSTAIN

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1 WATERSHED APPROACH TO RECOVERING URBAN STREAMS: MONTICELLO CREEK CASE STUDY USING SUSTAIN Eric LaFrance, Senior Stormwater Engineer, Public Works Department, Redmond, WA Tarelle Osborn, Osborn Consulting, Bellevue, WA ABSTRACT In 2013, Redmond approved a Citywide Watershed Management Plan, which focused resources on six priority watersheds, one of which is the Monticello Creek Watershed. Monticello Creek is located in northeast Redmond, and is one of the most rapidly growing parts of the City (see Figure 1). This growth has the benefit of allowing more people to live in Redmond, but it can also affect water quality and wildlife habitat. Increases in impervious surfaces associated with urbanization (e.g., roads, roofs, parking lots, etc.) result in degraded stream health, primarily because of the higher volumes and durations of the stormwater runoff. One of the parameters used to describe this effect is high flow pulse counts, which is defined by the number of times that twice the mean flow is exceeded for a time period. High pulse counts have shown a strong correlation with biologic stream health indicators. High pulse counts were selected to be used as the optimized parameter within the SUSTAIN model. A suite of possible projects were defined for the SUSTAIN model. The optimized results were then reality checked in a desktop exercise. Real world limits were placed on the possible number of each type of stormwater best management practice (BMP) within each modeled catchment and the model was rerun. The modeling results produced best solution scenarios over a range of costs. The solutions and costs were compared and a scenario was selected based on getting the highest return on investment. The selected scenario was essentially a list of projects that most effectively mitigated for high pulse counts. These projects were then prioritized using a defined methodology. The initial prioritization was developed prior to public input. The initial list was then used to develop an intensive public outreach program that included the public scoring these alternatives to produce a final prioritized project list. INTRODUCTION The City of Redmond (City) has identified factors critical to its vision of ensuring a clean and green environment for the future. To create and maintain a clean and green environment we must protect the natural resources that nourish and sustain us physically, emotionally, and spiritually. Maintaining and restoring healthy habitats and ecosystems will help accomplish our goals of clean air, water, and soil, while also nurturing our desire for beautiful places that can be enjoyed by the community. The City s responsibility to provide key services to protect the health of its community and the environment is a primary impetus behind this Citywide Watershed Management Plan (WMP). 1

2 Figure 1: Vicinity Map 2

3 The City has more than 50 miles of local creeks, three Class I Streams (Streams large enough to be considered waters of the state), and Lake Sammamish. These surface waters are valued City assets that have been adversely impacted by development. The WMP guides actions to restore these surface waters based on a holistic approach to surface water management. The plan identifies the target conditions to which we will restore our surface waters, major factors that play a role in surface water conditions, and opportunities to support and restore healthy surface waters. It prioritizes areas for action and sets a basis for measuring and evaluating performance. The WMP will help restore Redmond s surface waters by providing a coordinated framework for addressing multiple regulatory drivers, and support future development. Redmond is taking a watershed-based approach to surface water management to be more strategic with resources, projects, and programs. When applied city-wide, this approach is expected to produce more immediate and measurable positive results relative to the current approach that relies on uncoordinated regulatory drivers to achieve incremental, site-by-site improvements in stormwater management as land is developed or redeveloped over an extended period. Redmond is implementing this approach to achieve the goal of rehabilitating all the City s surface waters over the next 50 to 100 years. Redmond will target local streams based on existing habitat conditions. Streams that are only slightly impaired will be addressed first. This strategy will provide high quality habitat sooner, albeit in limited areas, as opposed to implementing incremental improvements in all streams that would not provide significant overall habitat benefits, potentially for decades. For streams that have significant degradation, the City will strive to lessen and eliminate further degradation until they are targeted for rehabilitation. Based on a thorough watershed assessment, the City has established four overall management strategies for Redmond s watersheds. 1. Protection: This management strategy category includes watersheds with fish bearing Class II streams that are considered relatively pristine. City actions in these watersheds will emphasize protection and preservation rather than rehabilitation. This category includes streams in the Redmond Watershed Preserve Park and Farrell McWhirter Park, which are Collin, Mackey, and Seidel creeks. 2. Highest Restoration: This management strategy category includes Bear, Clise, Evans, High School, Monticello, and Tosh Creeks. These watersheds have surface waters that are impaired but have the most potential to support all beneficial uses. City actions in these watersheds will focus on implementing watershed rehabilitation measures to improve and restore all beneficial uses. 3. Restoration: Watersheds with streams that are impacted by urbanization but still have potential to support beneficial uses with substantial investment are included within this management strategy category. Water quality is impaired, stream corridors are typically only partially intact, and instream complexity is limited. These include Perrigo, Peters, Tylers, and Willows Creeks, and the Sammamish River. 4. Restoration Development: Watersheds with streams significantly compromised in both the stream corridor as well as extensive impacts caused by watershed development are in this 3

4 management strategy category. Included are Lake Sammamish and the following creeks: Country, Idylwood, Sears, Valley Estates, and Villa Marina. The goal of the WMP is to eventually rehabilitate all of the City s impaired waterbodies. Furthermore, an interim goal has been established pursuant to the WMP to rehabilitate all waterbodies associated with Highest Restoration watersheds by In this context, the term rehabilitate means water quality standards will be met in each waterbody and the Benthic Index of Biotic Integrity (B-IBI) scores will be indicative of good (38 to 45) habitat conditions. MONTICELLO CREEK PRIORITIZED FOR RECOVERY Northeast Redmond, where Monticello Creek watershed is located, is one of the most rapidly growing parts of the city. This growth has many benefits, but it can also affect water quality and wildlife habitat and it can result in increased flooding and erosion. Increases in impervious surfaces associated with urbanization (e.g., roads, roofs, parking lots) result in degraded stream health, primarily because of the high volume and speed of stormwater runoff, which alters the natural flow of the stream. Stormwater infrastructure can be built to reduce impacts from development, better mimic natural stream flows during storms, and increase stream flow during the summer. The Monticello Creek Watershed was one of six priority watersheds identified in Redmond's 2013 Citywide Watershed Plan. The City is committed to fully restoring Monticello Creek to make it healthy for aquatic life and a valuable natural asset for the people who live, work, and play in Redmond. The first step in developing the Monticello Creek Watershed Restoration Plan is to identify and prioritize improvement projects. The restoration plan will identify potential stormwater retrofit and instream projects that will improve flow, water quality, and habitat of the creek. The City is using the US Environmental Protection Agency s (USEPA) optimization program, SUSTAIN, to identify potential stormwater retrofit projects on a basin scale. The projects in this plan will aim to: Enhance the stream channel and improve fish and wildlife habitat. Enhance stream banks (with native trees and shrubs) to improve fish and wildlife habitat. Control flooding and prevent erosion in the neighborhood (if any) to restore natural flow in Monticello Creek. Clean up stormwater runoff to prevent pollutants from entering our streams. Repair or replace failing pipes to make sure our stormwater management systems are protecting the environment and property from flooding. The watershed restoration plan will be supported by a robust monitoring program providing baseline information that will confirm modeling for project designs. Additionally, monitoring will be used to evaluate the effectiveness of constructed projects. With continuous monitoring and periodic updates to the plan, a progression of improvements can be documented and the program can change course, if needed. 4

5 WHAT IS SUSTAIN? SUSTAIN was developed in 2009 by Tetra Tech Inc. for the USEPA as a decision support system, designed to facilitate the selection and placement of stormwater best management practices (BMPs) to minimize the costs associated with meeting user specified objectives (e.g., flow control, pollutant load reduction). Although it s been around for some time, there are a limited number of SUSTAIN modeling applications that have been completed. In the Puget Sound region, King County has been using SUSTAIN in some of their larger watersheds, specifically the Green/Duwamish River and central Puget Sound watersheds in WRIA 9. The models are being used to generate a cost estimate and prioritization plan for systematically implementing stormwater BMPs and low impact development (LID) techniques in previously developed areas of WRIA 9. The key benefit of SUSTAIN is the optimization module which determines BMP locations, types, and design configurations that minimize the total project costs while achieving the desired water quality or flow control goals. To formulate an optimization problem, SUSTAIN requires the user to specify decision variables, assessment points, evaluation factors, and management targets. The result is an effectiveness curve charting the overall project costs relative to the effectiveness of whatever parameter was chosen for optimization. MONTICELLO SUSTAIN INPUTS & ASSUMPTIONS This section provides a very brief overview of the technical modeling and approach used to setup the Monticello Basin SUSTAIN model. HSPF Model Development & Calibration Subcatchment hydrology (both existing and future) must be simulated externally when using SUSTAIN s aggregate BMP approach. For this project, an external HSPF model was developed and calibrated prior to building the SUSTAIN model. Subcatchments were developed to a pretty micro level in order to create more accuracy in identification of the most effective locations for BMPs. Figure 2 shows the four subbasins and subcatchments that were delineated and modeled in the Monticello Watershed. SUSTAIN Parameters Optimization in SUSTAIN can be ran for various parameters. The project team decided to evaluate optimum BMP configurations in Monticello for high pulse count (HPC) that can be used to determine the predicted stream Benthic Index of Biotic Integrity (BIBI). Using HPC and associated BIBI as the optimization parameter accounts for flow control, flow normalization, and treatment all in one objective. The existing BIBI of Monticello is relatively high for an urban stream, with scores ranging from 20 to 40. However, the projected BIBI if nothing is done to limit impacts of development is much lower. The existing BIBI scores were collected by Redmond and King County staff between 2011 and To convert the SUSTAIN results from HPC to BIBI, the Snohomish County Regression Equation was determined to be the best and most applicable. 5

6 Best Management Practice Scenarios The project team specified and selected which BMPs would be included in the model based on the City s stormwater code and feasibility. Table 1 summarizes the various BMPs included in the model. Because of the relatively small basin size and City staff knowledge of the subcatchments, the BMP selection was very limited in terms of type and maximum number of units per subcatchment. These limitations were set in SUSTAIN to insure feasibility of model outputs (see Appendix A for additional detail on BMP limitations by basin). 6

7 Figure 2: Monticello Watershed Subbasins and Subcatchments 7

8 BMP design and sizing assumptions were developed by the project team. For common BMPs used in King County s WRIA 9 SUSTAIN model, the assumptions remained the same. For the more specialized BMPs, the specific design criteria, cost, and sizing were developed and imported into the SUTSAIN model. Table 1: BMPs Options Evaluated in SUSTAIN BMP Type Implementation Design Assumptions Rain Gardens City of Redmond Used WRIA 9 SUSTAIN Model Specs Bioretention Swale (Private) Private Development Used WRIA 9 SUSTAIN Model Specs Bioretention Swale (City) City of Redmond Used WRIA 9 SUSTAIN Model Specs Stormwater Pond Private Development Used WRIA 9 SUSTAIN Model Specs Cost Assumptions $120/SF 0$ $345/SF $0 Vault with Property Purchase City of Redmond 1.0 acres of impervious per unit $33.35/CF Vault within Right-of-Way City of Redmond 1.0 acres of impervious per unit $93.99/CF Existing Pond Expansion City of Redmond 1.0 acre of impervious per expansion $72.77/CF Filterra City of Redmond 0.4 acres of impervious per unit $54,000/each Deep Infiltration City of Redmond 2.0 acres of impervious per well $204,000/each Figure 3: Effectiveness Curve from SUSTAIN Results 8

9 MONTICELLO SUSTAIN RESULTS The results of the SUSTAIN modeling provided an effectiveness curve relative to the reduction in HPC and total project cost. After evaluating results and considering the overall watershed goals, the City selected to target a 60 percent reduction for a total investment of $12 million dollars. The curve was helpful in highlighting the diminishing return on investment beyond 60 percent. The SUSTAIN results help to identify the total watershed plan for restoration and protection in terms of the best configuration of BMPs totaling a $12 million investment for a 60 percent reduction. However, the SUSTAIN results do not provide a breakdown of effectiveness by BMP. Therefore, the project team looked for common themes in terms of BMP configurations in the best solutions produced and plotted near the top of the curve. This was paired with the team s knowledge of the basin to identify a list of 20 BMPs that will be carried forward to the next step of prioritization. These are public retrofit BMPs being added to the basin, separate from private development stormwater BMPs. Prioritization of BMPs will be completed using multi-objective criteria with input from all project stakeholders including the public. SUSTAIN MODELING LESSONS LEARNED / LIMITATIONS Outside of the King County Staff, contracted to complete the SUSTAIN modeling, this was the Project team's first exposure to SUSTAIN, naturally resulting in several lessons learned. Model Detail and Run Times The Monticello Basin SUSTAIN model was developed in great detail at every level, including the number of catchments and specificity of BMPs. This detail naturally results in longer the run times. SUSTAIN results are one big scatter plot, each with a different configuration of BMPs for each solution aimed at identifying an effectiveness curve. The added level of detail provides more credibility to the effectiveness curve, but it doesn t help in prioritizing which BMPs should be developed first. If the model was developed with larger catchments and more generic BMPs, the run times would have been quicker and the model could have been used to help identify the most effective BMPs types and where they should be located to be most effective. Planners proposing to use SUSTAIN need to determine what is most important, identify the overall watershed dollar investment, and have a high level of confidence in their determinations for using SUSTAIN to help prioritize BMP types and locations in the basin. SUSTAIN Resources The limited number of experienced SUSTAIN users resulted in the modeling taking much longer than anticipated. The contracting agency hired to complete the modeling had only a couple staff members proficient with the software and lost key staff through the life of the project, which presented challenges to the overall project schedule. Planners proposing to use SUSTAIN need to recognize the limitations of the software in terms of resources and experienced users. 9

10 APPENDIX A: MONTICELLO WATERSHED SUSTAIN MODEL BMP SELECTION