SWAT Literature Database for Peer-Reviewed Journal Articles

Modeling bacteria fate and transport in watersheds to support TMDLs 
Benham, B.L., C. Baffaut, R.W. Zeckoski, K.R. Mankin, Y.A. Pachepsky, A.M. Sadeghi, K.M. Brannan, M.L. Soupir, and M.J. Habersack 
Journal:Transactions of the ASABE 
Article ID: 
URL (non-DOI journals):http://ddr.nal.usda.gov/handle/10113/1401 
Broad Application Category:hydrologic & pollutant 
Primary Application Category:pathogen fate and transport 
Secondary Application Category:model comparison 
Watershed Description:
367 km^2 Shoal Creek (Missouri) 
Calibration Summary:
stream flow r2/NSE values (May 1999-June 2000): daily=0.40/0.21, monthly=0.70/0.63 
Validation Summary:stream flow r2/NSE values (June 2001-Sept 2002): daily=0.61/0.54, monthly=0.61/0.66 
General Comments: 
Abstract: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.