Water Resources Research Act Program

Details for Project ID 2012SD212B

Subsurface Drainage Impacts on Evapotranspiration and Water

Institute: South Dakota
Year Established: 2012 Start Date: 2012-03-01 End Date: 2014-02-28
Total Federal Funds: $39,286 Total Non-Federal Funds: $78,594

Principal Investigators: Christopher Hay, Jeppe Kjaersgaard, Todd Trooien

Abstract: Subsurface drainage has increased dramatically in eastern South Dakota with increases in precipitation, commodity prices, and land prices. Subsurface drainage improves agricultural production by increasing yields and reducing risk, but there are concerns about its environmental impacts. A key concern is to what extent does subsurface drainage contribute to downstream !ow alterations and !ooding through changes in the amount and timing of water leaving the "eld. Changes in evapotranspiration (ET), as a result of drainage, are a primary determinant of the hydrologic alterations from subsurface drainage. However, the impacts of drainage on ET are not yet well understood. Lack of such knowledge is an important problem, because without it, we are limited in our ability to accurately quantify the impacts of subsurface drainage on watershed hydrology and !ooding. DRAINMOD is a widely used computer simulation model designed to model the hydrology of high water table soils using water balance techniques. However, while DRAINMOD accounts for excess water stress limitations on crop yield from poor drainage, it doesnt account for reduced transpiration as a result of those yield reductions. #e FAO 56 dual-crop coe$cient method for calculating evapotranspiration, which includes a soil-water balance, will be used for comparison with the DRAINMOD ET estimates. #e FAO 56 dual-crop coe$cient method also allows for a crop stress coe$cient to adjust actual ET for crop stressors that can reduce ET, including excess water. ET calculated using the FAO 56 dual-crop coe$cient method, along with yield reductions estimated using DRAINMOD, will be used to develop plant stress coe$cients to account for excess water stress reductions on ET. #e crop stress coe$cients will be integrated into FAO 56 dual-crop coe$cient method ET estimates. #ese new ET estimates will then be used along with DRAINMOD estimates of the water balance components, including ET, to estimate the impact that reduced transpiration as a result of crop yield reductions due to excess water stress has on water yield. #e overall goal of this proposal is to develop a method to account for the impact of yield reductions from poor drainage on evapotranspiration in drainage model simulations. Our central hypothesis, based on water productivity functions that relate crop yield and ET, is that current drainage model simulations overestimate ET under undrained or poorly drained conditions. #e rationale for the proposed research is that once we are able to accurately simulate ET under undrained and poorly drained conditions, we can then better estimate the impacts that subsurface drainage development will have on hydrology. Our contribution here is expected to be an improved understanding of the impacts of subsurface drainage on ET. Once such knowledge is available, we can better evaluate the hydrologic impacts of increased subsurface drainage in eastern South Dakota.