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Catchment-scale hydrologic modeling of urban residential stormwater best management practices (BMPs)
YEAR: 2021
INVESTIGATORS: Breanna Marmur, Jannette Thompson

The combined effects of urbanization and projected climate changes are expected to increase the already negative effects of urban areas on surface water resources. Increased runoff volumes, flow rates, and pollutant loads due to impervious surfaces will likely be exacerbated by increased intensity and duration of storm events, leading to degraded aquatic ecosystems and impaired water quality. In Cedar Falls, Iowa (the location of our project study sites) segments of Dry Run Creek which feed into the Cedar River have both biological and bacterial impairments. New approaches to stormwater management known as green infrastructure and stormwater best management practices (BMPs) are designed to restore the natural hydrologic cycle, increasing infiltration, reducing runoff volumes and rates, and trapping/filtering pollutants in soil. These practices have the potential to improve water quality and the ecological integrity of aquatic systems, but additional research is needed to quantify these effects. Extensive monitoring and modeling of distributed small-scale BMPs is crucial to understanding how these practices can reduce the impacts of stormwater on surface water resources, as well as to improving the long-term resiliency of stormwater management infrastructure to adapt to future climate changes. Additional empirical data for stormwater runoff quantity and quality are also crucial to the development of realistic and reliable urban hydrologic simulations. Several parameters within hydrological models, especially those used to assess and predict water quality, require extensive monitoring for robust model calibration. Subsequent model validation is also best performed using data independent of that used in the calibration process. Due to the time- and cost-intensive nature of long-term monitoring and sampling studies, many hydrologic models are not based on site-specific flow or water quality data, leading to high levels of uncertainty about whether they represent “real world” scenarios. This proposal seeks support to extend efforts to monitor stormwater runoff quantity and quality from two “paired” residential neighborhoods in Cedar Falls. The extended period of monitoring proposed here (from two years of previous monitoring to three years) will provide the data needed for parameterization and robust calibration and validation of hydrologic and water quality models. This will also allow for comparison to and closer replication of a previous five-year study conducted in the Easter Lake Watershed in Des Moines. The specific objectives of this study of two residential watersheds in the Dry Run Creek Watershed are to: 1) Monitor stormwater quantity and quality during storm events for one additional year; 2) Collate independent data sets to parameterize, calibrate and validate water quantity and quality models for both watersheds; 3) Characterize stormwater BMP effects on runoff volume and water quality parameters; and 4) Predict possible hydrologic outcomes of varying levels of BMP adoption across spatial and temporal scales, including the effects of climate variability over time. The results of this study will allow a range of hydrologic and water quality outcomes to be quantified and simulated, and will ascertain the levels of BMP adoption necessary to achieve water quality goals. Additionally, results of climate change simulations can be used to provide long-term hydrologic predictions and to support urban resiliency planning.