Institute: South Dakota
Year Established: 2013 Start Date: 2013-03-01 End Date: 2014-02-28
Total Federal Funds: $20,526 Total Non-Federal Funds: $43,354
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. A recent estimate indicated that there are 3,926 pending applications to the USDA NRCS for wetland determinations in eastern South Dakota for the purposes of installing drainage systems. Subsurface drainage improves agricultural production by increasing yields and reducing risk, but there are concerns about its environmental impacts. Subsurface drainage alters !eld hydrology, which can have both positive and negative impacts on downstream water quantity and quality. 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. ET is generally the second largest component of the hydrologic cycle, and along with precipitation, determines how much water is available to leave the !eld via surface runo#, drain pipe out"ow, or deep seepage. 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. $ere has been much learned about the hydrologic impacts of subsurface drainage at the !eld scale as reported in comprehensive reviews by Robinson (1990), Skaggs et al. (1994), Robinson and Rycroft (1999), and Blann et al. (2009). However, the e#ects are complex, di%cult to generalize, and depend on a number of local factors (Skaggs et al., 1994; Blann et al., 2009). DRAINMOD is a widely used computer simulation model designed to model the hydrology of high water table soils using water balance techniques (Skaggs, 1980). DRAINMOD is relatively easy to use, when compared with many other hydrologic models, but provides accurate predictions of the hydrology of drained systems. DRAINMOD estimates ET based on potential ET calculated using either the default empirical, temperature-based $ornthwaite method or calculated separately using another method and directly input into DRAINMOD. Water limitations on actual ET are accounted for by limiting ET based on soil water availability. However, while DRAINMOD accounts for excess water stress limitations on crop yield from poor drainage, it doesn’t account for reduced transpiration as a result of those yield reductions. It is well established that there is a strong relationship between crop yield and transpiration, so this could be a important source of potential error in estimating the water yield (surface runo# plus drain pipe out"ow) when comparing drained and undrained scenarios where poor drainage has a strong impact on crop yield. Our contribution here is expected to be an improved understanding of the impacts of subsurface drainage on evapotranspiration. !e research proposed in this application is signi"cant, therefore, because it is expected to lead to improved predictions of the changes in water yield as a result of subsurface drainage. Once such knowledge is available, we can better evaluate the hydrologic impacts of increased subsurface drainage in eastern South Dakota.