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Accueil du site → Doctorat → États-Unis → 1998 → Effects of disturbance on soil properties and soil-water movement in an arid environment

University of Nevada, Reno (1998)

Effects of disturbance on soil properties and soil-water movement in an arid environment

Andraski, Brian Joseph

Titre : Effects of disturbance on soil properties and soil-water movement in an arid environment

Auteur : Andraski, Brian Joseph

Université de soutenance : University of Nevada, Reno

Grade : Doctor of Philosophy (PhD) 1998

Investigations of unsaturated flow in arid region soils are important in water resource analyses and in hydrologic assessment of existing and proposed waste-disposal sites. The overall objective of this research was to improve understanding of the mechanisms that affect soil-water movement under pristine and perturbed conditions. The effects of disturbance were evaluated in terms of differences between data collected under undisturbed conditions and data collected under simulated solid-waste-burial conditions in the Amargosa Desert, Nevada. Three manuscripts presented findings of the laboratory, field, and modeling components of the research. The laboratory study showed that construction of waste-burial trenches markedly altered the properties and variability of the natural site environment. Soil hydraulic properties were characterized using data measured over a water-content range that is representative of arid conditions but is seldom studied. Results showed that use of standard techniques can lead to significant errors in the description of hydraulic properties of dry soils. The multiple-year field study provided a greater understanding of how, and to what degree, the natural unsaturated-flow system can be altered by the installation of a waste-disposal facility. Naturally stratified soil in combination with native plants provided effective controls on the annual near-surface water balance and provided for episodic, deep drying of the unsaturated zone well below the apparent root zone during years with below-average precipitation. Under nonvegetated conditions, accumulation and shallow ($<$2 m) penetration of precipitation was observed ; at greater depths, however, hydraulically driven flow remained typically upward. Results suggested that isothermal liquid, isothermal vapor, and thermal vapor flow need to be considered in the conceptualization of unsaturated flow at the field sites. Computer simulations to compare a standard water-retention function (Brooks and Corey, 1964) and a full-range water-retention function (Rossi and Nimmo, 1994) showed that the full-range function improved tracking of measured drying trends in the surface-active zone under summer or prolonged drying conditions for a nonvegetated, native-soil site. Below a depth of 1 m, differences between water potentials and water fluxes estimated by the two models were small. Results indicated a need for further work to improve model predictions of wetting front advancement and water vapor movement in the unsaturated zone.

Mots clés : Soil sciences, Hydrology, Biological sciences, Earth sciences, Nev

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