Field Use of Soil Moisture Sensors to Study Water Flow Patterns.

Automated soil water content data are helpful to understand water flow in closed - depression landscapes, with gently slopes and shallow water table depths. Non-automated neutron probe data are useful for extending analysis to broader spatial areas. The purpose of this study is to show how closed - depression landscapes are affected by water table variation and upward water movement. Neutron probe soil water determinations average over a larger area than automated sensors. The newer automated sensors may not average as well across non-uniform soil water contents and some are sensitive to temperature effects. Separate calibrations for different water content and temperature ranges helps overcome these limitations. Because of calibration uncertainty, analyses based on difference in soil water content are more useful than those based on absolute soil water content. Automated soil water measurements were used as part of a water balance to detect net upward water movement into the measurement zone (< 0.9 m). Out of 53 days without rain in 2006, 37, 43, and 36 days had net upward water movement for shoulder, backslope, and toeslope positions. The mean amount of water moving upward was 2.6, 3.2, and 3.1 mm per day for shoulder, backslope, and toeslope positions for a mean evapotranspiration rate of 4.0 mm per day. Soil water and upward water movement depend strongly on water table depth. Water table depth depends strongly on landscape position because of subsurface lateral redistribution.