Comparison of performance of tile drainage routines in SWAT 2009 and 2012 in an extensively tile-drained watershed in Midwest

Authors: GUO, TIAN - Purdue University; GITAU, MARGARET - Purdue University; MERWADE, VENKATESH - Purdue University; Arnold, Jeffrey; SRINIVASAN, RAGHAVAN - Texas A&M University; HIRSCHI, MICHAEL - University Of Illinois; ENGEL, BERNARD - Purdue University

Submitted to: Hydrology and Earth System Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/14/2017
Publication Date: 2/16/2017
Publication URL: https://handle.nal.usda.gov/10113/5931469
Citation: Guo, T., Gitau, M., Merwade, V., Arnold, J.G., Srinivasan, R., Hirschi, M., Engel, B. 2017. Comparison of performance of tile drainage routines in SWAT 2009 and 2012 in an extensively tile-drained watershed in Midwest. Hydrology and Earth System Sciences. 1-33. https://doi.org/10.5194/hess-2017-52.
DOI: https://doi.org/10.5194/hess-2017-52

Interpretive Summary: Large regions of the Midwest U.S. were swamps and wetlands that have been drained with subsurface tiles and are now productive agricultural regions. However, the tiles provide a direct conduit for nitrogen to reach water bodies. In this study, we tested new tile drainage and runoff routines with the SWAT (Soil and Water Assessment Tool). SWAT was developed to predict the impact of climate and land use change on river flows and water quality. The model was validated for the Little Vermillion watershed in Illinois. Results confirmed that the new tile and runoff routines improved prediction of stream tile flow and nitrate loads. The results of this study provide more accurate representation of basic tile flow processes, which then provides more accurate conservation planning.

Technical Abstract: Subsurface tile drainage systems are widely used in agricultural watersheds in the Midwestern U.S. Tile drainage systems enable the Midwest area to become highly productive agricultural lands, but can also create environmental problems, for example nitrate-N contamination associated with drainage waters. The Soil and Water Assessment Tool (SWAT) has been used to model watersheds with tile drainage. SWAT2012 revisions 615 and 645 provide new tile drainage routines. However, few studies have used these revisions to study tile drainage impacts at both field and watershed scales. Moreover, SWAT2012 revision 645 improved the soil moisture based curve number calculation method, which has not been fully tested. This study used long-term (1991–2003) field site and river station data from the Little Vermilion River (LVR) watershed to evaluate performance of tile drainage routines in SWAT2009 revision 528 (the old routine) and SWAT2012 revisions 615 and 645 (the new routine). Both routines provided reasonable but unsatisfactory uncalibrated flow and nitrate loss results. Calibrated monthly tile flow, surface flow, nitrate-N in tile and surface flow, sediment and annual corn and soybean yield results from SWAT with the old and new tile drainage routines were compared with observed values. Generally, the new routine provided acceptable simulated tile flow (NSE'='0.50–0.68) and nitrate in tile flow (NSE'='0.50–0.77) for both field sites with random pattern tile and constant tile spacing, while the old routine simulated tile flow and nitrate in tile flow results for the field site with constant tile spacing were unacceptable (NSE'='-0.77– -0.20 and -0.99–0.21 respectively). The new modified curve number calculation method in revision 645 (NSE'='0.56–0.82) better simulated surface runoff than revision 615 (NSE'='-5.95'~'0.5). Calibration provided reasonable parameter sets for the old and new routines in LVR watershed, and the validation results showed that the new routine has the potential to accurately simulate hydrologic processes in mildly-sloped watersheds.