City of Davenport WRR19-002
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Davenport Sponsored Project Application Concept DUCK CREEK WATERSHED ASSESSMENT SUMMARY This sponsored project application focuses on the Duck Creek watershed and urban runoff and bacterial impairment issues being experienced therein. A watershed assessment, called the Duck Creek Watershed Management Plan (DCWMP), was completed for Duck Creek in 2011 (Appendix A). The DCWMP illustrates a correlation between impervious surface and bacterial loads. The sub-watersheds with the highest bacterial loads are the ones with the most impervious surface area. Therefore, addressing urban runoff from impervious surfaces is a key focus of this application. Duck Creek Watershed – Bacterial Impairment The Duck Creek Watershed is located entirely in Scott County, Iowa. The watershed encompasses the urban sectors of the city of Davenport, the city of Bettendorf and rural Scott County (see Figure 1). Duck Creek is not supporting two of the intended uses of the stream: primary contact recreation (Class A1 use) and children’s recreation, (Class A3 use). Primary contact recreation includes activities that involve direct contact with the water such as swimming and wading. Children’s recreation is similar, but specific to activities or locations where children contact the water. Neither designated use is currently supported in Duck Creek due to high levels of indicator bacteria called Escherichia coli (E. coli) measured in the stream. High E. coli levels in a waterbody can indicate the presence of potentially harmful bacteria and viruses (also called pathogens). Humans can become ill if they come into contact with and/or ingest water that contains pathogens. Sources of bacteria in the Duck Creek Watershed are as follows: 1. During high flows – pet waste 2. During medium flows – cattle 3. During low flows – cattle and septics 4. Spring “moist” conditions – manure application 5. Summer “dry” conditions – cattle and septics Duck Creek Watershed – Urban Runoff Although urban runoff is not listed on the 303d list of impairments, it and its associated pollutants are an area of concern for Duck Creek. Urban runoff is a key concern in the Duck Creek Watershed because urbanized areas accumulate pollutants on streets, rooftops and other surfaces. During rainfall or snowmelt, these pollutants are mobilized and transported to Duck Creek. Key pollutants commonly found in urban runoff are bacteria, nitrogen, phosphorus, pesticides, sediment and hydrocarbons. Sub-watersheds with the largest percent impervious surface in Duck Creek experience the greatest bacterial loads. Therefore, addressing urban runoff from impervious surfaces is a key component of this sponsored 1 project application. Within Duck Creek urban areas, another pollutant of concern is high nitrate concentration from lawn runoff. The Iowa Nutrient Reduction Strategy (INRS) estimates that the Major Land Resource Area (MLRA) including the city of Davenport is the third largest contributor of nitrogen from lawn fertilization in the state.1 Collecting and treating runoff from urban areas using water filtration and infiltration practices will reduce pollutant loadings. By treating urban stormwater runoff, the city of Davenport will address a major source of Duck Creek’s bacterial impairment. In addition, practices to reduce nutrient loads will also be helping the State of Iowa achieve its INRS goal of reducing the State’s nutrient loads to the Mississippi River. Figure 1: Duck Creek Watershed Jurisdictional Map 1 Iowa Nutrient Reduction Strategy, Revised Version (October 1, 2014), section 2, p. 20. 2 PROJECT GOALS AND OBJECTIVES Goals The main goals of this sponsored project application are to reduce bacteria loads in Duck Creek, reduce urban runoff from the city of Davenport, and reduce nutrient loads to the Mississippi River. Objectives The main objective of this application is to implement large and small scale best management practices (BMPs) throughout the Duck Creek Watershed to help reduce bacteria, nitrogen, phosphorus, pesticides, sediment and hydrocarbons from urban and agricultural sources. Another objective of this application is to implement best management practice recommendations from the DCWMP in targeted areas of the watershed to help address the bacterial impairment in Duck Creek. BEST MANAGEMENT PRACTICES Per the Iowa Stormwater Management Manual (ISMM), BMPs that reduce urban runoff, bacteria, nitrogen, phosphorus, pesticides, sediment and hydrocarbons include: 1) Bioretention Cells, 2) SQR and 3) Wetlands. Prairie reconstruction can be utilized as an agricultural BMP to reduce runoff, bacteria, nutrient and sediment loads. Other projects recommended in the DCWMP to address Duck Creek’s bacterial impairment are as follows: 1) Urban BMP Cost-Share Program, 2) Septic System Repairs and 3) a Pet Waste Campaign. Below are descriptions of each BMP. Bioretention Cells Bioretention systems incorporate shallow landscaped level depressions that temporarily store and readily infiltrate runoff. They include both rain gardens and bioretention cells. Bioretention cells typically include a rock chamber, subdrain, and modified soil mix. In bioretention cells, stormwater runoff collected in the upper layer of the system is filtered through the surface vegetation, mulch layer, pervious soil layer, and then stored temporarily in a stone aggregate base layer. Typically, bioretention cells are planted with native prairie species. Soil Quality Restoration Healthy soil is the key to preventing polluted runoff. As buildings and houses are built topsoil is removed and the remaining subsoil is compacted by the grading and construction activity. The owner is left with heavily compacted subsoil, usually with a high clay content and little organic matter after construction is complete. Yards with poor, compacted soil contribute to water quality problems due to their inability to absorb water or infiltrate it to the roots of turfgrass. Compacted soil also requires more fertilizers and pesticides, both of which could end up in runoff and contribute to pollution in our local creek and streams. 3 Soil quality restoration (SQR) is the process of improving soil health on new or existing lawns. SQR reduces compaction, increases pore space, improves organic matter content, and re-establishes populations of soil dwelling organisms (microbes, worms, insects, etc.) on soils disturbed during construction. On existing turf grass, SQR is accomplished using deep tine aeration and a blanket of compost to restore organic matter to the soil profile. Ultimately, SQR leads to healthier, more functional soils and to landscapes that can absorb more rainfall. Wetlands Wetlands are a management practice designed and constructed to address the quality and quantity of stormwater runoff. Stormwater rates and volumes are decreased by absorption, evapotranspiration and outlet restrictions. Pollutant removal is accomplished by settling, biochemical reactions and plant uptake. They are most appropriate in locations where a continuous base flow or high-water table can assist in sustaining a permanent pool of water to support aquatic vegetation to the soil profile. Prairie Reconstruction Converting land use from row crops to native prairie eliminates nutrient application to the converted area while increasing rainwater infiltration and soil water holding capacity resulting in less water runoff. With less runoff, sediment, nutrients, and bacteria from manure applications are less likely to be transported to associated water bodies. In addition, native prairies enhance habitat for wildlife and insects including pollinators. Other BMPs Recommended in DCWMP Urban BMP Cost-Share Program The DCWMP identified a city-sponsored urban BMP cost-share program as a key component in addressing Duck Creek’s bacterial impairment. A Stormwater BMP Cost- Share Program provides property owners financial and technical assistance in implementing stormwater BMPs for improving water quality and reducing the amount of stormwater runoff from their property. Financial assistance helps cover the cost of materials and/or contractor labor for completing the projects. Projects can range from rain gardens and bioretention cells to pervious pavement and soil quality restoration. The city of Davenport could provide cost-share for both residential and commercial property owners for as part of this application. Septic System Repairs Cost-Share Program The DCWMP identified septic system repairs as a key component in addressing Duck Creek’s bacterial impairment. A potential opportunity to improve water quality in Duck Creek using sponsored Project funds would be for the City to cost-share septic system repairs with interested land owners whose septic systems are not functioning correctly. Pet Waste Campaign The DCWMP identified a Pet Waste Campaign as a key component in addressing Duck Creek’s bacterial impairment. A Pet Waste Campaign is an outreach activity conducted to educate pet owners how their animal’s waste contributes to water quality problems. Pet 4 Waste Campaign activities can include any or all of the following: passing out pet waste bags and dispensers, posters, magnets, press releases, bill stuffers, pet waste management survey cards, pet guide to neighborhood pollution prevention. Although recommended in the DCWMP, a Pet Waste Campaign in not eligible for Sponsored Project dollars and therefore is not being considered as a potential project for this application. PRIORITY AREAS IN DUCK CREEK WATERSHED Based on information shown in Figures 2 and 3, the following