Water Balance Approach to Determine Upward Water Movement

Shallow water tables can contribute water moving up into the root zone. The purpose of this study was to quantify upward moving water. Automated sensors were used to monitor soil water content and water table depth on sites in Central Iowa, which had varying shallow water tables. Tipping bucket raingage and Eddy covariance evapotranspiration (ET) measurements completed the water balance. Upward water movement ranges were determined from water balance and uncertainties for each component (rain, ET, change in soil water). The water table was more shallow for a toeslope position (0.5 to 1.4 m), and deepest for a shoulder position (1.3 to 3 m). Upward moving water was significantly higher in the toeslope position than for the shoulder position on 1/3 of the nonrain days, and significantly higher than the backslope position on 3/10 of the nonrain days. Upward moving water was significantly higher for the backslope position than the shoulder position on 1/4 of the nonrain days. On another toeslope site, there were spikes of increased soil water on rain days. These were attributed to lateral additions during the time the water table depth was within the sand lens located 1 to 1.5 m below the surface. The quantified upward water movement contributed to soil water storage.