Modeling the hydrologic influence of subsurface tile drainage using the
National Water Model
Abstract
Subsurface tile drainage (TD) is a dominant agriculture water management
practice in the United States (US) to enhance crop production in
poorly-drained soils. Assessments of field- or watershed-level
(<50 km2) hydrologic impacts of tile
drainage are becoming common; however, a major gap exists in our
understanding of regional (>105 km2)
impacts of tile drainage on hydrology. The National Water Model (NWM) is
a distributed 1-km resolution hydrological model designed to provide
accurate streamflow forecasts at 2.7 million reaches across the US. The
current NWM lacks tile drainage representation which adds considerable
uncertainty to streamflow forecasts in tile-drained areas. In this
study, we quantify the performance of the NWM with a newly incorporated
tile drainage scheme over the heavily tile-drained Midwestern US.
Implementing a tile drainage scheme enhanced the uncalibrated model
performance by about 20% to 50% of the calibrated NWM (Calib).
The calibrated NWM with tile drainage (CalibTD) showed enhanced
accuracy with higher event hit rates and lower false alarm rates than
Calib. CalibTD showed better performance in high-flow
estimations as tile drainage increased streamflow peaks (14%), volume
(2.3%), and baseflow (11%). Regional water balance analysis indicated
that tile drainage significantly reduced surface runoff (-7% to -29%),
groundwater recharge (-43% to -50%), evapotranspiration (-7% to
-13%), and soil moisture content (-2% to -3%). However, infiltration
and soil water storage potential significantly increased with tile
drainage. Overall, our findings highlight the importance of
incorporating the tile drainage process into the operational
configuration of the NWM.