Simulation of streamflow and wetland storage, Starkweather Coulee subbasin, North Dakota, water years 1981-98

A study was conducted to simulate streamflow and wetland storage within a part of the Starkweather Coulee subbasin.  Information on streamflow and wetland storage in Starkweather Coulee subbasin may help with the management of water issues in the Devils Lake Basin.  Information from a digital elevation model and geographic-information-system analyses of the study area was used to develop the Devils Lake Basin wetlands model.  Digital elevation model data and other climatic and topographic data were used as inputs to the model.  Within the study area, the average wetland depth was about 2.21 feet, the total maximum wetland area was about 30,890 acres at the overflow elevation, and the total maximum wetland volume was about 68,270 acre-feet.

 Model runs were made for water years 1981-98 to calibrate the model to observed streamflows that were obtained from the Starkweather Coulee gaging station.  Observed annual peak streamflows were greater than simulated annual peak streamflows for all water years except 1983.  The differences probably were caused mostly by the lack of a subroutine in the model to account for frozen soil.  The largest amount of simulated daily wetlands area occurred in April 1997 when about 40,500 acres of the study area was covered with water.  Also during April 1997, the simulated daily water volume in the open and closed wetlands combined attained a maximum of about 116,000 acre-feet.  By increasing the spillage thresholds from 0.2 to 1.0, simulated streamflow was reduced by 8.77 inches (from about 17.88 to 9.11 inches; 49 percent) for the 18-year period.  During water years 1994-98, simulated annual streamflows for open-wetland spillage thresholds of 1.0 remained less than for thresholds of 0.2 even though the open wetlands probably were near maximum volume.  The greatly increased size of the closed wetlands during water years 1994-98 probably allowed for increased water storage and decreased simulated streamflow from the study area.