Browsing by Author "Brannan, Kevin M."

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    BMP impacts on sediment and nutrient yields from an agricultural watershed in the coastal plain region
    Inamdar, S. P.; Mostaghimi, Saied; McClellan, P. W.; Brannan, Kevin M. (American Society of Agricultural and Biological Engineers, 2001)
    The goal of the Nomini Creek watershed monitoring study was to quantify the effectiveness of BMPs at the watershed scale and to determine if the improvements in water quality could be sustained over a long-term period. Information on the long-term effectiveness of BMPs is critical since BMPs are being implemented under the state cost-share program to reduce nonpoint source pollution (NPS) to the Chesapeake Bay. The Nomini Creek project started in 1985 and was completed in 1997. A pre- versus post-BMP design was used. A combination of managerial and structural BMPs was implemented. Major BMPs implemented in the Nomini Creek watershed included no-tillage, filter strips, and nutrient management. The data collected at the 1463 ha Nomini Creek watershed consisted of land use, hydrologic, water quality, soils, and geographical information. The BMPs implemented at Nomini Creek reduced average annual loads and flow-weighted concentrations of nitrogen (N) by 26% and 41%, respectively. Average annual total-N loads discharged from the watershed were reduced from 9.57 kg/ha during the pre-BMP period to 7.05 kg/ha for the post-BMP period. Largest reductions were observed for dissolved ammonium-N, soluble organic-N, and particulate-N. In contrast, nitrate-N loads increased after BMP implementation. Increase in nitrate exports was likely due to ammonfication and nitrification, and subsequent leaching of particulate-N species that were conserved on the field. In comparison to N, reductions in phosphorus (P) loads and concentrations were not significant. BMP implementation resulted in a mere 4% reduction for total-P with a corresponding 24% reduction in flow-weighted concentration. The average annual total-P loads exported from the watershed were 1.31 and 1.26 kg/ha for the pre- and post-BMP periods, respectively. Reductions in total-P loads were due to decreases in particulate-P. Exports of ortho-P and dissolved organic-P increased after BMP implementation. It is likely that some of this post-BMP increase in dissolved P fractions was associated with dissolution and leaching of particulate-P, and higher rainfall-runoff activity in the watershed during the post-BMP period. In comparison to nutrients, there was no significant change in suspended solids discharged from the watershed. Overall, the findings of this study indicate that the BMPs were effective in reducing the losses of some forms of nutrients, such as ammonium-N and particulate-P, from the Nomini Creek watershed, but additional BMIs are necessary to achieve significant reductions in all forms of N and P.
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    Modeling bacteria fate and transport in watersheds to support TMDLs
    Benham, Brian L.; Baffaut, C.; Zeckoski, Rebecca Winfrey; Mankin, K. R.; Pachepsky, Y. A.; Sadeghi, A. A.; Brannan, Kevin M.; Soupir, M. L.; Habersack, M. J. (American Society of Agricultural and Biological Engineers, 2006)
    Fecal contamination of surface waters is a critical water-quality issue, leading to human illnesses and deaths. Total Maximum Daily Loads (TMDLs), which set pollutant limits, are being developed to address fecal bacteria impairments. Watershed models are widely used to support TMDLs, although their use for simulating in-stream fecal bacteria concentrations is somewhat rudimentary. This article provides an overview of fecal microorganism fate and transport within watersheds, describes current watershed models used to simulate microbial transport, and presents case studies demonstrating model use. Bacterial modeling capabilities and limitations for setting TMDL limits are described for two widely used watershed models (HSPF and SWAT) and for the load-duration method. Both HSPF and SWAT permit the user to discretize a watershed spatially and bacteria loads temporally. However, the options and flexibilities are limited. The models are also limited in their ability to describe bacterial life cycles and in their ability to adequately simulate bacteria concentrations during extreme climatic conditions. The load-duration method for developing TMDLs provides a good representation of overall water quality and needed water quality improvement, but intra-watershed contributions must be determined through supplemental sampling or through subsequent modeling that relates land use and hydrologic response to bacterial concentrations. Identified research needs include improved bacteria source characterization procedures, data to support such procedures, and modeling advances including better representation of bacteria life cycles, inclusion of more appropriate fate and transport processes, improved simulation of catastrophic conditions, and creation of a decision support tool to aid users in selecting an appropriate model or method for TMDL development.
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    Stream discharge measurement using a large-scale particle image velocimetry (LSPIV) prototype
    Harpold, A. A.; Mostaghimi, Saied; Vlachos, Pavlos P.; Brannan, Kevin M.; Dillaha, Theo A. III (American Society of Agricultural and Biological Engineers, 2006)
    New technologies have been developed for open-channel discharge measurement due to concerns about costs, accuracy, and safety of traditional methods. One emerging technology is large-scale particle image velocimetry (LSPIV). LSPIV is capable of measuring surface velocity by analyzing recorded images of particles added to the stream surface. LSPIV has several advantages over conventional measurement techniques: LSPIV is safer, potentially automated, and produces real-time measurements. Therefore, the goal of this study was to evaluate the accuracy and feasibility of using LSPIV to measure instantaneous discharge in low-order streams. The specific objectives were: (1) to determine optimum operating parameters for applying LSPIV under various conditions, (2) to design, develop, and test a prototype under controlled laboratory conditions, and (3) to develop and test the field equipment for a variety of streamflow conditions. The laboratory experiment results indicated that LSPIV accuracy was influenced by camera angle, surface disturbances (Froude number), and flow tracer concentration. Under field conditions, the prototype acquired consistent images and performed image processing using accepted input parameters. The accuracy of LSPIV for use infield applications was evaluated using a permanent weir. Overall, 18 discharge measurements were taken with each measuring device. The LSPIV prototype was accurate, with a mean error of -1.7%, compared to the weir measurements. The root mean square error (RMSE) was similar for LSPIV and current meter discharge measurements with the area-velocity method when compared to the weir. Finally, the LSPIV discharge measurements had an uncertainty of approximately +/- 14% (at a 95% confidence level). Therefore, LSPIV showed the potential to become competitive with conventional discharge measurement techniques.