HR: 0800h
AN: H21E-1394    [Abstracts]
TI: Field-Measured Infiltration Properties of Mojave Desert Soils
AU: * Perkins, K S
EM: kperkins@usgs.gov
AF: USGS, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Nimmo, J R
EM: jrnimmo@usgs.gov
AF: USGS, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Winfield, K A
EM: kariwinf@yahoo.com
AF: USGS, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Schmidt, K M
EM: kschmidt@usgs.gov
AF: USGS, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Miller, D M
EM: dmiller@usgs.gov
AF: USGS, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Stock, J D
EM: jstock@usgs.gov
AF: USGS, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Singha, K
EM: ksingha@geosc.psu.edu
AF: Pennsylvania State University, Department of Geosciences, 311 Deike Building, University Park, PA 16802 United States
AB: Characteristics typical of alluvial desert soils, such as depositional stratification, desert pavement, biotic crusts, and vesicular horizons strongly influence soil moisture and its variability. Knowledge of infiltration capacity, water retention, and unsaturated hydraulic conductivity is central to the assessment of water availability to plants and animals after infiltration events. These hydraulic parameters are directly related to the degree of soil development. The frequency and magnitude of storm events in conjunction with degree of soil development also affect runoff and erosion. Our purpose is to examine field soil-water behavior and determine unsaturated hydraulic properties needed for large-scale modeling of soil moisture. The results of this study will be used in conjunction with surficial geologic mapping of the Mojave Desert in evaluations of ecological habitat quality. We conducted infiltration/redistribution experiments on three different-aged deposits in the Mojave National Preserve: (1) recently deposited wash sediments, (2) a soil of early Holocene age, and (3) a highly developed soil of late Pleistocene age. In each experiment we ponded water in a 1-m-diameter infiltration ring for 2.3 hr. For several weeks we monitored water content and matric pressure to depths of 1.5 m, and distances of 6 m from the infiltration ring. Measuring techniques included surface electrical resistance tomography, dielectric-constant probes, heat-dissipation probes, and tensiometers. Analysis of the subsurface measurements using an instantaneous-profile technique gives the retention and K properties that will be used in predictive modeling. In each experiment the infiltration rate was nearly constant in time, with infiltration capacity 4 times greater in the youngest than in the oldest soil. Average infiltration flux densities within the ring during the period of ponding were 0.80 m/hr in the active wash, 0.45 m/hr in the Holocene soil, and 0.21 m/hr in the Pleistocene soil. All three deposits have significant gravel (30-70% within the uppermost 1.5 m) with the percentage of silt and clay increasing with deposit age. The low infiltration capacity in the oldest soil is consistent with the presence of the more highly developed vesicular horizon and accumulation of illuvial silt. Depositional stratification in the active wash did not impede downward flow to the same degree as in the early Holocene-age soil, which has some soil horizon development and sparse biotic crust. Infiltrated water spread laterally to at least 1 m beyond the ring perimeter at all sites; the presence of a buried clay-rich horizon in the active wash enhanced spreading at depth to 2 m.
UR: http://wwwrcamnl.wr.usgs.gov/uzf
DE: 1865 Soils (0486)
DE: 1866 Soil moisture
DE: 1875 Vadose zone
DE: 1895 Instruments and techniques: monitoring
SC: Hydrology [H]
MN: Fall Meeting 2005