Ground Freezing Effects on Soil Erosin of Army Training Lands Part 2: Overwinter Changes to Tracked-Vehicle Ruts, Yakima Training Center, Washington

Two areas were monitored at the Yakima Training Center (YTC( in central Washington to measure changes in M1A2 Abrams (M1) tank-rut surface geometry, and in- and out-of-rut saturated hydraulic conductivity (Kfs), soil penetration resistance (SPR), and bulk density over the 1995-1996 winter. Profile meter data show that rut cross-sectional profiles smoothed significantly and that turning ruts did so more than straight ruts. Rut edges were zones of erosion and sidewall bases were zones of deposition. Kfs values were similar in and out of ruts formed on soil with 0-5% water by volume, but were lower in ruts formed on soil with aobut 15% water. Mean SPR was similar in and out of ruts from 0- to 5-cm depth, increased to 2 MPa outside ruts and 4 MPa inside ruts at 10- to 15-cm depth, and decreased by 10-38% outside of ruts and by 39-48% inside ruts at the 30-cm depth. Soil bulk density was similar in and out of ruts from 0- to 2.5-cm depth, and below 2.5 cm it was generally higher in ruts formed on moist soil, with highest values between 10- and 20-cm depth. Conversely, density in ruts formed on dry soil was similar to out-of-rut depths. This information is important for determining impacts of tank ruts on water infiltration and soil erosion, and for modifying the Revised Universal Soil Loss Equation (RUSLE) and the Water Erosion Prediction Project (WEPP) models to more accurately predict soil losses on Army training lands.