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Title: SWAT application in low-gradient Coastal Plain landscapes

Author
item Bosch, David
item Arnold, Jeffrey
item VOLK, M - Helmholtz Centre
item ALLEN, P - Baylor University

Submitted to: Annual International SWAT Conference
Publication Type: Proceedings
Publication Acceptance Date: 6/1/2013
Publication Date: 7/16/2013
Citation: Bosch, D.D., Arnold, J.G., Volk, M., Allen, P.M. 2013. SWAT application in low-gradient Coastal Plain landscapes. In: Proceedings of the 2013 International SWAT Conference. Toulouse, France. July 15-19, 2013. 11 pp..

Interpretive Summary: The Coastal Plain region of the United States extends 3500 km from the state of New Jersey in the Northeast to Texas in the South-central. Physical features of the Coastal Plain including it’s flat terrain, high groundwater tables, and diverse soils make computer simulation of the hydrology of regional watersheds particularly challenging. Several studies describing simulation of the hydrology of the Little River Experimental Watershed in South-central Georgia, USA utilizing the Soil and Water Assessment Tool were reviewed. These studies show a consistent pattern of under-predicting high flow conditions in the winter period and over-estimating baseflow conditions in the summer period. Recent improvements to the model including greater spatial representation, parameter variation throughout the year, and sub-daily time steps provide a means for improving the hydrologic simulations for Coastal Plain watersheds. These improvements promise to yield more reliable information about the characteristics of these watersheds.

Technical Abstract: Low-gradient coastal plain watersheds present unique challenges for watershed modeling. Broad low-gradient floodplains with considerable in-stream vegetation contribute to low-velocity streamflow. In addition, direct interaction between streamflow and surficial aquifers must also be considered. Here we examine several efforts that have involved application of the Soil and Water Assessment Tool (SWAT) to the Little River Experimental Watershed (LREW) in South-central Georgia within the Coastal Plain region of the US. Specific objectives include: 1) Examine prior attempts to model the hydrology and water quality of the LREW; 2) Summarize the outcomes of prior SWAT modeling attempts; 3) Identify consistent weaknesses in the computer simulations; and 4) Propose guidance for future applications. Climatic and hydrologic data from the LREW were used. Results indicate streamflow timing and groundwater contributions can be managed through parameter adjustment. While calibrated SWAT simulations provide acceptable water balances, discrepancies remain between simulated and observed streamflow for periods where large rainfall events occur during seasonably dry summer conditions. SWAT revisions, including the grid version of SWAT, better landscape differentiation, parameter variation throughout the year, differentiation of slow-return and fast-return groundwater flow, and sub-daily time steps, should yield improved representation of hydrology within Coastal Plain watersheds