Relationship between geomorphic settings and unsaturated flow in an arid setting

Abstract

Abstract. Because geomorphology can readily be mapped, our ability to characterize unsaturated flow over large areas would be greatly enhanced if relationships between geomorphic settings and unsaturated flow could be identified. The purpose of this study was to evaluate relationships between geomorphic settings and spatial and temporal variability in unsaturated flow at a field site in the Chihuahuan Desert of Texas. This study differs from most previous studies in the variety of geomorphic settings studied, including drainage areas (Blanca Draw and Grayton Lake playa) and interdrainage areas (basin-fill deposits, eolian sheets, alluvial fans, and a fissure), density of data (-- Noninvasive techniques, such as electromagnetic (EM) induction and ground-penetrating radar, are becoming increasingly popular for evaluating unsaturated flow because they can be used to evaluate unsaturated flow rapidly over large areas and because they provide an evaluation of conditions between point measurements from boreholes. In an Australian study the correlation coefficient r between apparent electrical conductivity and recharge estimated according to unsaturated zone chloride data was 0. The geomorphic evolution of the landscape was described by Scanlon et al. [1999]. The study area has been subdivided into interdrainage and drainage areas. The interdrainage area consists of fine-grained basin-fill deposits and eolian sheets surrounded by a narrow rim of alluvial fans at the margin of the basin. An earth fissure is also found in the interdrainage area. The drainage area includes Bianca Draw and Grayton Lake.-The floor of Eagle Flat basin consists mostly of muds overlain by the Arispe Surface, which has well-developed soils. The basin-fill deposits are overbank deposits from the braided streams and from the toes of the alluvial fans. These deposits are stable, vegetated landforms that do not exhibit channels or erosional or depositionai features resulting from fluvial or alluvial activity. Three calcic soil horizons are found at depths of 0 to 1, 3, and 6 m, which suggest extremely stable conditions Boreholes were drilled with a hollow-stem auger without any drilling fluid, and samples were collected with a split spoon. Particle-size analyses were conducted on sediment samples from 37 boreholes using sieving and hydrometer analyses [Gee (Figure 1 and Table A1). Many samples were collected from the same boreholes as those that had been sampled for texture. To determine Samples were collected for tritium analysis from boreholes EF 79 and EF 117 in the interdrainage eolian sheet, EF 92 beneath the fissure, EF 96 10 rn from the fissure, and GL 2 in Grayton Lake. Water was extracted from core samples in the laboratory by toluene azeotropic distillation and purified using paraffin wax [Ingraham and Shadel, 1992]. The samples were enriched and analyzed using liquid scintillation methods at the University of Arizona Tritium Laboratory or using gas proportional counting at the University of Miami Tritium Laboratory. 4.Results and Discu...

Ecological controls on water-cycle response to climate variability in deserts

“…1). Water potential profiles based on laboratory measurements on soil cores collected in the field provide information on the direction of water movement because water moves from regions of high to low potential (14)(15)(16)(17). Chloride, which is derived from atmospheric precipitation and dry fallout at the land surface, moves into the soil with infiltrating water.…”

Technical Basis Document No. 1: Climate and Infiltration

“…Within the repository footprint, the greatest subsurface lateral flow is expected to occur at its western boundary, where the net infiltration rates are generally highest ( Figure C-6). If lateral flow were to occur at a scale larger than the 30-by-30-m gridblock size, then it would likely occur as flow at the bedrock-soil interface in these slopes (Scanlon et al 1999;Newman et al 1998). The most likely result of such lateral flow would be redistribution of water from slopes to the valley regions.…”

“…Proper land surface characterization is thus crucial for the evaluation of processes controlling net infiltration. Topography may cause the infiltration rate to vary by several orders of magnitude under different geomorphic settings (Scanlon et al 1999). …”

Special Analysis for the Disposal of the Consolidated Edison Uranium Solidification Project Waste Stream at the Area 5 Radioactive Waste Management Site, Nevada National Security Site, Nye County, Nevada

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