Incorporation of Hooghoudt and Kirkham tile drain equations into SWAT2005

Authors: Moriasi, Daniel; Arnold, Jeffrey; Rossi, Colleen

Submitted to: Annual International SWAT Conference
Publication Type: Proceedings
Publication Acceptance Date: 6/18/2007
Publication Date: 7/2/2007
Citation: Moriasi, D.N., Arnold, J.G., Rossi, C.G. 2007. Incorporation of Hooghoudt and Kirkham tile drain equations into SWAT2005. Proceedings of the Annual International SWAT Conference, July 2-6, 2007, Delft, The Netherlands. p. 139-147.

Interpretive Summary: Agricultural tile drainage is a common water management practice in agricultural regions with seasonal water table depths near the ground surface such as the Midwest U.S. Too much water in the root zone, as a result of shallow water tables, is undesirable for crop production because it can lead to poor aeration. A watershed-scale computer model, SWAT2005, was modified to allow for multiple scenario simulations to determine cost-effective water management systems. This was achieved by incorporating into SWAT2005 the methods adopted from another computer model, DRAINMOD, which has been tested and widely used to successfully predict the performance of drainage and water table control systems in crop fields. These methods were successfully incorporated into the SWAT2005 model. In order to validate the enhanced model, tests are underway in three watersheds located within Muscatatuck River Basin in southeast Indiana and in the South Fork Watershed in north central Iowa. Once validated the modified SWAT2005 model will enable in-expensive multiple scenario simulations such as varying tile spacing, tile depth, and tile size to aid in designing cost-effective water management systems. In addition, the enhanced SWAT2005 model will be useful in determining the effect of existing tile drainage on water quality and quantity at the watershed-scale.

Technical Abstract: Agricultural tile drainage is a common water management practice in agricultural regions with seasonal high water tables such as the Midwest U.S. The goal of this study was to modify SWAT2005 to enable it to perform multiple scenario simulations to determine cost-effective water management systems at the watershed scale. This was accomplished by incorporating the Hooghoudt steady-state and Kirkham tile drain equations. The Hooghoudt steady-state and Kirkham equations have been successfully used in DRAINMOD, a computer simulation model that has been tested and widely used to simulate the performance of drainage and water table control systems on a continuous basis at field-scale. These equations depend on maximum depressional storage (Sd). Sd, which is assumed constant in DRAINMOD, is allowed to change in the modified SWAT2005 model as a function of dynamic soil random roughness. The dynamic random roughness is a function of tillage type and intensity and amount of rainfall. The drainage flux is calculated using a three-step approach. 1) Hooghoudt steady-state equation is used when the water table is below the surface or Sd; 2) Kirkham equation is used to compute the ponded surface drainage flux when the water table rises to completely fill the surface; and 3) when the drainage flux predicted by the appropriate equation is greater than the design drainage capacity (also known as drain coefficient (DC)), then the flux is set equal to DC. These algorithms were successfully incorporated into SWAT2005 and the enhanced SWAT2005 is currently undergoing validation. The modified SWAT2005 shows great potential for use in some of the Conservation Effects Assessment Project (CEAP) benchmark watersheds such as South Fork Watershed in north central Iowa.