Tile drainage simulation in SWAT2012: Parameterization and evaluation in an Indiana watershed

Authors: BOLES, CHELSIE - Purdue University; FRANKENBERGER, JANE - Purdue University; Moriasi, Daniel

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2015
Publication Date: 6/1/2015
Citation: Boles, C.M., Frankenberger, J.R., Moriasi, D.N. 2015. Tile drainage simulation in SWAT2012: Parameterization and evaluation in an Indiana watershed. Transactions of the ASABE. 58(5):1201-1213.

Interpretive Summary: Subsurface tile drainage is a commonly used agricultural practice to enhance crop yield in poorly drained but highly productive soils in many other regions of the world. Hydrologic and water quality models such as the Soil and Water Assessment Tool (SWAT) are widely used to simulate tile drainage systems at various spatial scales. However, few studies have been published that test the newly modified SWAT drainage routine. In this study, 1) the new drainage routine was implemented in a small, agricultural watershed in Indiana to demonstrate how parameters can be selected based on knowledge of typical drainage systems and drainage design theory, and 2) the simulated results obtained using the new drainage algorithms were evaluated against both measured streamflow and nutrient data as well as tile flow amounts from literature review. Replacing the previous tile equation with the Hooghoudt and Kirkham drainage equations and a drainage coefficient was found to result in a tile drain system which exhibited decreased peaks and longer storage time. Most of the new tile drain parameters such as tile drain depth, radius, and spacing, and the drainage coefficient for the study area were acceptably valued based on real systems. However, the maximum surface depressional storage parameter that controls surface runoff and the parameter that estimates lateral saturated hydraulic conductivity were obtained through the calibration process because they are either not physically measurable or difficult to measure. Therefore, the parameter values obtained in this can provide a basis for further work to fine-tune drainage tile parameterization. Overall, this study found that the SWAT drainage routine using the new tile drainage equations can be used in the calibration of a model that appropriately simulates both streamflow and nutrient export.

Technical Abstract: In the poorly drained soils of the Midwestern United States, subsurface drainage is an important flow pathway in the agricultural landscape; it therefore needs to be included in modeling studies. The new tile drainage simulation method in the Soil Water Assessment Tool (SWAT), based on the Hooghoudt and Kirkham equations, has had limited application but shows promise for predicting drainage impact in drained watersheds. The objectives of this study were to: 1) implement the new drainage routine in a small, agricultural watershed in Indiana, demonstrating how parameters can be selected based on knowledge of typical drainage systems and drainage design theory, and 2) to evaluate model predictions for this tile drainage routine and determine the impact of the new tile drain algorithm on outputs. When tile drains were implemented on 50.9% of the watershed, simulated tile flow was found to vary between 8.5% and 16.2% of annual precipitation. Streamflow and nutrient outputs were compared to measured values. Monthly Nash-Sutcliffe efficiency (NSE) values for streamflow exceeded 0.70 in all calibration and validation