The sensitivity to land use and climate variations in the whitewater river basin, kansas, USA: Closing the water budget using groundwater models

A water budget was developed using groundwater models to assess the impact of land use and climate variability on the Whitewater River Basin located in southeastern Kansas within the ARM-SGP as part of the DOE Water Cycle Pilot Study. The Whitewater River Basin has an area of 1,100 km2, an elevation range of 380 - 470 m above mean sea level, and an average annual precipitation of 858 mm. Time series and geospatial analysis are used to identify significant spatial structure and dominant temporal modes in the watershed runoff and groundwater response. Space-time analyses confirmed the hydrogeologic conceptual model developed from the hydrostratigraphic information provided by existing geologic studies and over 2,000 wells located in the area. The groundwater-surface water interactions are identified by time series analysis of stream discharge, precipitation, temperature, and water levels in wells. Singular spectrum analysis suggests a two layer leaky perched system with strong influences of daily, monthly, seasonal, and interannual oscillations. The geospatial analysis identifies the important length scales and the time series analysis the corresponding time scales, which must be incorporated in the model. The fine scale layering, which creates the perched leaky top layer, was represented by using an anisotropy ratio. This ratio was determined from select well data to be 100 (Kh/Kv), by calculating the vertical conductivity from harmonic mean and horizontal conductivity from arithmetic mean. MODFLOW is used to assess the importance of groundwater when attempting to close the water budget. The R-squared value between MODFLOW predicted and observed head values for the watershed was 0.85 indicating a good fit. Mean recharge was estimated to be approximately 17 percent of total annual precipitation. The approach presented here is an initial attempt to examine the importance of groundwater in the water budget of a relatively small river basin.