Submitted to: Geological Society of America Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 8/20/1998
Publication Date: N/A
Technical Abstract: Military maneuvers damage vegetation, break up soil crusts, loosen surface soil, change soil-surface geometry, compact soils and often form ruts which enhance surface flow channelization much like natural rills. All these impacts directly affect soil erodibility and runoff erosivity. Our objective was to measure the effects of soil freeze-thaw (FT) cycling on compacted soil in vehicle ruts and on the geometry of ruts and natural rills. We established research sites at Yakima Training Center (YTC) in southcentral Washington in December 1995 and at Ethan Allen Firing Range (EAFR) in northwestern Vermont in October 1996. The mean length of the freezing season at YTC is 50-60 days and at EAFR, 110-120 days. Observations over one winter at YTC show: 1) tank-rut profiles smoothed as sediment from rut crests slid into the rut; 2) mean penetration resistance and bulk density below 5 cm depth in ruts were statistically higher than out of ruts, especially when the soil contained 15% water by volume during tracking; 3) saturated hydraulic conductivity was lower in 75% of straight ruts made on soil with 15% water, lower yet in turning ruts, and not statistically different in and out of ruts when tracking on soil with 5% water; and, 4) surface-water runoff began sooner and runoff rates were 67 to 77% higher in ruts than on adjacent, unrutted soil due to decreased infiltration in ruts. EAFR observations showed that: 1) incipient rills and a distinct v-shaped, 11-cm deep rill formed in ruts while adjacent, untrafficked soils showed no rill initiation; 2) scattered sidewall slumps occurred along deeper rills during spring thaw; 3) unconfined compressive strength of the surface soil in tank ruts decreased by 60%, in wheel paths by 50% and in untrafficked soil by 29% due to soil-FT cycling.