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ARS Home » Plains Area » Temple, Texas » Grassland Soil and Water Research Laboratory » Research » Publications at this Location » Publication #312856
Title: Improvement of the variable storage coefficient method with water surface gradient as a variable

Author
item JEONG, J - Texas Agrilife Research
item WILLIAMS, J - Texas Agrilife Research
item MERKEL, W - Natural Resources Conservation Service (NRCS, USDA)
item Arnold, Jeffrey
item WANG, X - Texas Agrilife Research
item ROSSI, C - Bureau Of Land Management

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/22/2014
Publication Date: 10/5/2014
Publication URL: http://handle.nal.usda.gov/10113/60431
Citation: Jeong, J., Williams, J.R., Merkel, W.H., Arnold, J.G., Wang, X., Rossi, C.G. 2014. Improvement of the variable storage coefficient method with water surface gradient as a variable. Transactions of the ASABE. 57(3):791-801.

Interpretive Summary: Hydrological models simulate the impact of climate and land use on the magnitude and frequency of floods and droughts. Models are also used to design flood control structures. Several flood routing models were tested within the framework of the APEX (Agricultural Policy/ Environmental eXtender) and SWAT (Soil and Water Assessment Tool) models. The methods were shown to compare well with the HEC-RAS model developed by the U.S. Corps of Engineers, except in some watersheds with steep slopes. The results indicate that the APEX and SWAT models can be accurately predict flood magnitude and frequency this making them useful tools in developing plans for flood mitigation.

Technical Abstract: The variable storage coefficient (VSC) method has been used for streamflow routing in continuous hydrological simulation models such as the Agricultural Policy/Environmental eXtender (APEX) and the Soil and Water Assessment Tool (SWAT) for more than 30 years. APEX operates on a daily time step and offer options for simulating processes on shorter time steps (e.g., hourly). However, APEX is not adequate for applications such as designing flood control structures or estimating flood damages because of a fundamental assumption in the VSC method: the normal flow condition. The storage with variable slope (SVS) method and an enhanced variable storage coefficient (VSCe) method are proposed as new routing methods for continuous simulation models that will improve flow routing and water quality simulation at subdaily time scales. This study describes the principle of the SVS method and the VSCe method and their performances against HEC-RAS unsteady flow results for various hydraulic and geometric conditions. Results show that the peak flow and the time to peak flow improved by up to 20% with SVS and VSCe on mild slopes (less than 0.0005 m m-1) and small time steps of less than 1 h when compared to the conventional VSC method, although the difference narrowed as the channel slope and time interval increased. A case study on a small agricultural watershed in Texas indicates that both VSCe and VSC are reliable in watershed applications, but the improvement in streamflow prediction can be marginal in watersheds with steep slopes.