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Ellicott City, MD, United States

Collins K.A.,Center for Watershed Protection | Arnold C.L.,University of Connecticut | Kitchell A.C.,Horsley Witten Group
ASABE - TMDL 2010: Watershed Management to Improve Water Quality | Year: 2010

In 2006, the Connecticut Department of Environmental Protection issued an impervious cover (IC) Total Maximum Daily Load (TMDL) for the Eagleville Brook watershed, located on the University of Connecticut campus and the adjacent Town of Mansfield, CT. While traditional TMDLs typically target a specific pollutant, this one addresses the impacts of urban development directly by using IC as the TMDL's metric. This approach was chosen because the Eagleville Brook Watershed's biological impairment could not be attributed to any one pollutant, but rather, was ascribed to an array of pollutants transported by stormwater and linked to urbanization or, more specifically, impervious cover (IC). The existing IC in the Eagleville Brook Watershed was measured at 18.0%, but the TMDL target was set at 11% based on characteristics of similarly sized watersheds in Connecticut that had healthy macroinvertebrate populations. The project objective was to reduce the amount of effective, or hydrologically directly connected to a stream or drainage system, IC in the watershed by either removing IC directly or by treating impervious cover using low impact development techniques. The project team conducted a stormwater retrofit inventory within the watershed, and identified 110 opportunities to treat or disconnect impervious cover on the University of Connecticut campus. Although IC is used to measure progress in this TMDL, the ultimate success will be the restoration of the biological communities in the Eagleville Brook watershed by improving the stream's habitat and water quality. Since the start of this project, additional IC TMDLs are under development or have been developed in CT, ME, NC, and MA. As such, this project could set a national precedent for using impervious cover in a regulatory framework for implementing low-impact development (LID) practices at the watershed-scale. Source

Christianson L.,Conservation Fund | Christianson L.,Iowa State University | Christianson R.,Center for Watershed Protection | Helmers M.,Iowa State University | And 2 more authors.
Journal of Irrigation and Drainage Engineering | Year: 2013

Design methods for agricultural drainage denitrification bioreactors must be optimized for these novel systems to provide maximized water quality improvement. The objective of this paper was to further develop science-based bioreactor sizing guidelines by calibrating an existing design procedure with multiple years of drainage flow data collected at two sites in Iowa. The models created for the two hypothetical bioreactor sites showed the original design criteria (use of a design flow rate one-fifth of the peak flow rate) generally allowed simulated bioreactor treatment of the majority of total annual drainage volume, but treatment of this majority was not necessary to maximize nitrate removal. Larger bioreactors resulting from use of either increased design flow rate or higher design retention time increased the extent of nitrate removal, but had lower nitrate removal rates. This modeled simulation analysis informs that bioreactor design procedures considering flow rate and retention time should use design flow rates of 10 to 20% of the anticipated peak flow rate at design retention times of 6 to 8 h, thus updating and refining the original design procedure. This approach produces bioreactors of increased length to width ratios, with improved performance based on nitrate removal extent and removal rate. Further field-scale validation is suggested for this drainage bioreactor design procedure. © 2013 American Society of Civil Engineers. Source

Christianson R.D.,Center for Watershed Protection | Hutchinson S.L.,Kansas State University | Brown G.O.,Oklahoma State University
Journal of Hydrologic Engineering | Year: 2016

Estimates of the USDA-NRCS runoff curve number (CN) are generally based on a soil map and observed land cover. Because the CN method is increasingly applied to disturbed and urbanized land, the objective of this work was to collect effective saturated hydraulic conductivities, Ksat, and sorptivities, So, from a range of land use types, use the results to estimate a CN, and compare these CNs with CN estimates made from soil survey information and corresponding land cover. A total of 331 double ring infiltration tests were conducted over the 15 sites. Based on land use and site history, the test sites were classified into categories of engineered, urban altered, rural altered, rural unaltered, and prairie. Measured Ksat values were skewed so the medians of these data were a better predictor of central tendency. The prairie and rural unaltered median Ksat values were closer to soil map estimates than the other categories (between 0.0 and 91% different from soil survey). Two empirical methods developed in Hawaii using sprinkle infiltration tests were used to estimate CN values from infiltration data; method 1 used only Ksat as the predictor and method 2 used Ksat and So. Results from these two methods were not statistically different at 12 of the 15 sites (α = 0.05). When comparing these methods to CN values developed from soils data and land cover (method 3), better overall agreement existed between method 1 and method 3. The median CN value from method 1 was the best predictor for the mean CN based on measured runoff data for an urban altered land use site (0.6% different), whereas method 3 was the best predictor for the mean CN based on measured runoff data for a prairie land use (0.0% different). © 2015 American Society of Civil Engineers. Source

Christianson R.D.,Center for Watershed Protection | Brown G.O.,Oklahoma State University | Barfield B.J.,Oklahoma State University | Barfield B.J.,Woolpert Inc. | Hayes J.C.,Clemson University
Transactions of the ASABE | Year: 2012

With the implementation of Phase II of the National Pollutant Discharge Elimination System (NPDES), municipalities have new requirements to reduce stormwater quantity and enhance water quality. Bioretention cells (BRCs) are a pollution mitigation option that can address the new regulations. In order to implement BRCs in the landscape, models are needed so stormwater engineers and managers can estimate the impact of the mitigation technique. While several BRC models are available, users must supply input parameters, which are many times poorly understood. The objective of this work was to determine the level of input specificity in hydraulic parameters needed to accurately estimate water movement through a BRC. A water movement model was developed that incorporates infiltration, drainage, and overflow for a single storm event. Then pilot-scale BRCs were constructed and operated to obtain data for model testing. The model was run with four sets of input parameters with increasing specificity: soil type, fraction sand/silt/clay, an adjustment for bulk density, and a macropore routine to serve as a fitting parameter. While the model with the highest input specificity proved to match experimental values closest (drainage volume between 0.7% and 8.8% from observed, and maximum drainage flow rate between 1.4% and 18% from observed), it is unlikely that stormwater managers would have access or time to obtain this information. However, a simulation with the fraction sand/silt/clay and an adjustment for bulk density provided acceptable results (drainage volume between 0.7% and 18% from observed, and maximum drainage flow rate between 30% and 39% from observed). © 2012 American Society of Agricultural and Biological Engineers. Source

Christianson R.D.,Center for Watershed Protection | Brown G.O.,Oklahoma State University | Chavez R.A.,Oklahoma State University | Storm D.E.,Oklahoma State University
Transactions of the ASABE | Year: 2012

To address increasing stormwater management concerns in metropolitan and suburban areas, bioretention systems are a mitigation technology that helps address both water quantity and quality. However, it is critical for stormwater managers and engineers to model the hydraulic performance of these systems before investing in the infrastructure. This means an appropriate model must be selected to efficiently reflect important aspects of the given site and design. This work investigated the ability of a one-dimensional model to simulate water movement through a heterogeneous bioretention cell. For model validation, two full-size bioretention cells in Grove, Oklahoma, were flooded a total of three times, and parameters related to overflow, drainage and relative change in soil moisture were measured. Observed values were compared to predictions using an uncalibrated model previously developed and run with area-weighted soil parameters ("original model"). In addition, observations were compared to an uncalibrated "revised model," which allowed modeling of distinct infiltration media. The revised model allowed for two separate soil types in the horizontal plane and simulated maximum subsurface drainage flow rate (23.6% to 33.7% from observed), volume (7.9% to 38.9% from observed), and timing (14.7% to 92.5% from observed) better than the original model, but the original model generally simulated overflow volume (12.2% to 77.1% from observed) and peak overflow rate (3.6% to 9.6% from observed) more closely. It was concluded that the revised model was more appropriate for modeling heterogeneous systems when concerns exist about timing of hydrographs and all underdrain parameters. © 2012 American Society of Agricultural and Biological Engineers. Source

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