Modeling the Effects of Tile Drain Placement on the Hydrologic Function of Farmed Prairie Wetlands

Abstract

The early 2000s saw large increases in agricultural tile drainage in the eastern Dakotas of North America. Agricultural practices that drain wetlands directly are sometimes limited by wetland protection programs. Little is known about the impacts of tile drainage beyond the delineated boundaries of wetlands in upland catchments that may be in agricultural production. A series of experiments were conducted using the well‐published model WETLANDSCAPE that revealed the potential for wetlands to have significantly shortened surface water inundation periods and lower mean depths when tile is placed in certain locations beyond the wetland boundary. Under the soil conditions found in agricultural areas of South Dakota in North America, wetland hydroperiod was found to be more sensitive to the depth that drain tile is installed relative to the bottom of the wetland basin than to distance‐based setbacks. Because tile drainage can change the hydrologic conditions of wetlands, even when deployed in upland catchments, tile drainage plans should be evaluated more closely for the potential impacts they might have on the ecological services that these wetlands currently provide. Future research should investigate further how drainage impacts are affected by climate variability and change.

Prairie Pothole Region Wetlands and Subsurface Drainage Systems: Key Factors for Determining Drainage Setback Distances

“…Thus, shallower systems would have greater potential to affect wetland hydrology when solely relying on the setback distance to limit such effects. Werner et al (2016) concluded that changes to wetland period of inundation in a low-relief terrain were more sensitive to the depth of an SDS than to the distance (i.e., setback) from a wetland, substantiating the importance of considering SDS characteristics such as depth when assessing potential effects to wetland hydrology.…”

“…Subsurface drainage systems (SDSs) are used throughout the United States to enhance agricultural production by facilitating water management. Historically, use of SDSs has been prevalent in the southeastern portions of the PPR (Iowa, Minnesota); however, use of these systems expanded rapidly into North Dakota and South Dakota (hereafter, Dakotas) during the 2000s in response to rising commodity prices, most notably corn, which peaked around 2012 (Roth and Capel 2012;Johnston 2013;Finocchiaro 2016;Werner et al 2016). Subsurface drainage systems typically consist of perforated drainage pipe placed in various configurations below the soil surface to target specific areas (e.g., wetlands) or manage the water table of entire fields.…”

“…Subsurface drainage systems situated beneath a wetland basin that often include a surface-inlet pipe can drain wetlands through direct removal of ponded surface water and subsurface soil pore water. Subsurface drainage systems placed in the surrounding contributing area of the catchment can indirectly affect wetland water balances through a reduction in water inputs from precipitation runoff (Tangen and Finocchiaro 2017) or by enhancing the downward or horizontal movement of water from a wetland through the lateral effect of the SDS (Werner et al 2016). The effect of an SDS on a wetland's hydrology depends on factors such as topography, soils, and properties of the SDS such as size (pipe diameter, linear distance) and location (horizontal and vertical) of the drain pipe relative to the wetland (Werner et al 2016;Tangen and Finocchiaro 2017).…”

“…Although relevant research is sparse, a recent modeling study suggested that farmed prairie wetlands could have shortened periods of inundation and lower water depths depending on where SDSs are situated within a wetland's catchment (Werner et al 2016). Moreover, a recent field study of prairie wetlands demonstrated that precipitation runoff from the catchment can be an important component of a wetland's seasonal water balance that could be affected by an SDS (Tangen and Finocchiaro 2017).…”

“…Overall, these studies suggest that SDSs located adjacent to wetlands can affect their hydrology by varying degrees, depending on factors such as depth of drainage pipe, distance of the SDS from wetland, slope gradient (e.g., high-, low-relief terrain), soil properties, and groundwater connection (recharge, discharge). In fact, period of inundation, water depth, or ponded surface area could be reduced by greater than 50% under certain scenarios (Werner et al 2016;Tangen and Finocchiaro 2017). For this study, we assessed information used for prescribing lateral setback distances to identify important SDS and catchment characteristics to consider when establishing drainage-related policies for conservation lands.…”