Submitted to: Annual International SWAT Conference
Publication Type: Abstract Only
Publication Acceptance Date: 5/24/2010
Publication Date: 8/4/2010
Citation: Moriasi, D.N., Arnold, J.G., Vazquez-Amabile, G.G., Engel, B.A., Rossi, C.G. 2010. New shallow water table depth algorithm in SWAT2005: recent modifications [abstract]. Annual International SWAT Conference, August 2-6, 2010, Seoul, South Korea. p. 19. Available on-line: http://swatmodel.tamu.edu/docs/swat/conferences/2010/Book-of-Abstracts.pdf Interpretive Summary: Abstract only.
Technical Abstract: The proximity of the shallow water table depth (wtd) to the soil surface impacts agricultural production, farm machine trafficability, and water quality due to agricultural chemical transport and soil salinity. Therefore, it is essential for hydrologic models to accurately simulate wtd. Recently, an alternative shallow wtd algorithm that relates drainage volume (vol) to wtd was incorporated into the Soil and Water Assessment Tool (SWAT Release 2005) model. Water table depth is computed as a function of vol and a factor wtdconv, which converts vol into wtd. The conversion factor wtdconv is currently a calibration parameter that is a function of the soil physical properties. However, at the watershed-scale where there are many fields (hydrologic response units, HRUs), it is difficult if not impossible to determine an optimum wtdconv value for each HRU through the calibration process. The objectives of this study were to: 1) modify the alternative shallow wtd algorithm in SWAT2005 so that wtdconv is automatically computed by the model as a function of soil physical properties and the location of the wtd, in order to eliminate determination of wtdconv through the calibration process; and 2) evaluate the modified wtd algorithm within SWAT2005 using measured water table depth data for three soils located in forest fields without tile drainage within the Muscatatuck River basin in southeast Indiana. On average the calibrated wtdconv yielded daily calibration and validation Nash-Sutcliffe efficiency (NSE) values of 0.64 and 0.41, respectively, the percent bias (PBIAS) values of -13% and -4%, respectively, and root mean square error (RMSE) values of 0.41 m and 0.59 m, respectively, while the automatic wtdconv yielded NSE values of 0.65 and 0.48, respectively, PBIAS values of -3% and 1%, respectively, and RMSE values of 0.40 m and 0.55 m, respectively, for the three observation wells. Based on these model outputs, there were no significant differences between the wtd simulated using the manually calibrated and the automatically computed wtdconv coefficient. Automatically computed coefficient wtdconv will enable this alternative shallow wtd algorithm to be used at the watershed scale.