Browsing by Author "Zeckoski, Rebecca Winfrey"

Now showing 1 - 3 of 3
  • Thumbnail Image
    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.
  • Thumbnail Image
    Simulation of Runoff and Pollutant Loss in Urbanizing Watersheds
    Zeckoski, Rebecca Winfrey (Virginia Tech, 2002-05-08)
    The effect of urbanization on previously agricultural watersheds is an increasingly important issue for watershed planners. Urbanization increases runoff and pollutant loadings to the watershed outlet. Watershed planners in areas that previously had little impervious cover must now consider the effects of new roads and buildings on hydrologic processes. The ANSWERS-2000 watershed model was modified to simulate watersheds with mixtures of agricultural and urban areas. In addition, components were added to simulate atmospheric deposition and urban management practices, including wet ponds, dry ponds, and infiltration trenches. The modified model was evaluated on two watersheds in Blacksburg, Virginia, including a subwatershed of Stroubles Creek and a large parking lot on the Virginia Tech campus with a dry pond at its outlet. The model predicted the hydrology and pollutant losses for the year 1999 from the Stroubles Creek watershed within 50% of the observed values after calibration. Prediction errors were much higher for the parking lot and dry pond simulation of the period of time from August 1995 to February 1996. For the parking lot inflow to the dry pond, errors ranged from 0 to 100%. For the dry pond effluent, errors for runoff and sediment losses were -11.5 and 60.1%, respectively, and nutrient losses were poorly predicted (greater than 100% error). There was considerable uncertainty as to the quality of the observed data and this may account for some of the predicted sediment and nutrient loss errors. The modified model was applied to the Battlefield Green Watershed in Hanover County, Virginia to demonstrate the watershed response to development in that watershed. As simulated, sediment and nutrient losses were 30 to 50 times higher after development. The model is intended for use on watersheds with an impervious cover of 30% or less, due to the increased difficulty in accurately quantifying the hydrology of highly urbanized watersheds and because of uncertainty in atmospheric deposition rates on such watersheds. The pond subroutines are very simplified, and limit simulation to ponds with simple geometries.
  • Thumbnail Image
    Streamside Livestock Exclusion: A Tool for Increasing Farm Income and Improving Water Quality
    Zeckoski, Rebecca Winfrey; Benham, Brian L.; Lunsford, C. (Virginia Cooperative Extension, 2012-12-13)
    Describes selected reasons for implementing streamside livestock exclusion fencing, and briefly describes how to implement streamside livestock exclusion fencing.