Quantification of best management practice effectiveness for water quality protection at the watershed scale
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Stormwater runoff is the leading cause of water quality impairment in the United States (USEPA, 1996). Continued rapid urbanization and population growth have exacerbated this problem. Traditional urban development increases the imperviousness of land, resulting directly in increased runoff volume and peak runoff, decreased time to concentration, and deteriorated water quality (Dietz, 2007). Urban runoff contaminants include heavy metals, oil, grease, and particulates from fuels, and brake pads and tires wear from roads and parking lots (Kim et al., 2007) as well as nutrients, sediments, and pesticides from urban landscapes (Davis, 2007). Due to the increased flow rates, urban development requires expensive pipe networks to discharge the fluid to nearby watercourses or sewer systems (Scholz and Grabowiecki, 2007). These issues have resulted in reevaluation of traditional urban water management and a new emphasis on sustainable practices (Heaney et al., 1999).Low impact development (LID) is an approach to stormwater management that tries to minimize the effect of urbanization rather than focus on conveyance and routing and discharge. LID is being increasingly adopted as an alternative to traditional water systems. LID includes practices such as bioretention, green roofs, rainwater harvesting, and permeable pavements. While recent studies have evaluated the effectiveness of LID practices in various regions in the United States (Davis, 2007; Davis, 2008; Dreelin et al., 2006; Bean et al., 2007), there remains a great need to evaluate these practices in the field and to collect quantitative data on LID practices performance for different soil-hydrologic conditions. There is a paucity of data on the potential impact of the LID practices at watershed level. Sample and Heaney (2006) stated that the lack of such research is caused by the difficulty of modeling processes at the small scale required by low impact development (LID) management options. In this project, bioretention, rainwater harvesting, permeable pavements, and stream restoration will be evaluated as BMPS that will reduce stormwater runoff volume and peak flow and improve the water quality of the discharged water.Bioretention areas use the chemical, biological, and physical properties of soils, flora, and microorganisms to remove or retain pollutants from stormwater (Hinman, 2005). There are many designs for bioretention areas, but, typically, these areas consist of a mixture of soil planted with native or adapted plants that receives stormwater from a contributing area (Davis, 2008). Bioretention areas promote infiltration, storage, and slow release of water (Hinman, 2005). Very few studies have evaluated bioretention areas as a tool that targets parking lot stormwater retention and treatment at parking lot scale.Rainwater harvesting is an ancient practice that has been receiving increased attention around the world due to water shortages from droughts, pollution, and population growth (Fewtrell and Kay, 2007; Nolde, 2007; Sazakli et al., 2007; Meera and Ahameed, 2006).Although rainwater harvesting is commonly mentioned in literature as a stormwater..........