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Title: Arid site water balance: evapotranspiration modeling and measurements

In order to evaluate the magnitude of radionuclide transport at an aird site, a field and modeling study was conducted to measure and predict water movement under vegetated and bare soil conditions. Significant quantities of water were found to move below the roo of a shallow-rooted grass-covered area during wet years at the Hanford site. The unsaturated water flow model, UNSAT-1D, was resonably successful in simulating the transient behavior of the water balance at this site. The effects of layered soils on water balance were demonstrated using the model. Models used to evaluate water balance in arid regions should not rely on annual averages and assume that all precipitation is removed by evapotranspiration. The potential for drainage at arid sites exists under conditions where shallow rooted plants grow on coarse textured soils. This condition was observed at our study site at Hanford. Neutron probe data collected on a cheatgrass community at the Hanford site during a wet year indicated that over 5 cm of water drained below the 3.5-m depth. The unsaturated water flow model, UNSAT-1D, predicted water drainage of about 5 cm (single layer, 10 months) and 3.5 cm (two layers, 12 months) for the same time period. Additionalmore » field measurements of hydraulic conductivity will likely improve the drainage estimate made by UNSAT-1D. Additional information describing cheatgrass growth and water use at the grass site could improve model predictions of sink terms and subsequent calculations of water storage within the rooting zone. In arid areas where the major part of the annual precipitation occurs during months with low average potential evapotranspiration and where soils are vegetated but are coarse textured and well drained, significant drainage can occur. 31 references, 18 figures, 1 table.« less
Authors:
;
Publication Date:
OSTI Identifier:
6320610
Report Number(s):
PNL-5177
ON: DE85003090
DOE Contract Number:
AC06-76RL01830
Resource Type:
Technical Report
Research Org:
Pacific Northwest Lab., Richland, WA (USA)
Country of Publication:
United States
Language:
English
Subject:
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS; 12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; 54 ENVIRONMENTAL SCIENCES; MOISTURE; ENVIRONMENTAL TRANSPORT; TRANSPIRATION; SOILS; DRAINAGE; ARID LANDS; GRASS; HANFORD RESERVATION; LOW-LEVEL RADIOACTIVE WASTES; RADIOACTIVE WASTE DISPOSAL; UNDERGROUND DISPOSAL; MANAGEMENT; MASS TRANSFER; MATERIALS; NATIONAL ORGANIZATIONS; PLANTS; RADIOACTIVE MATERIALS; RADIOACTIVE WASTES; US DOE; US ERDA; US ORGANIZATIONS; WASTE DISPOSAL; WASTE MANAGEMENT; WASTES 053000* -- Nuclear Fuels-- Environmental Aspects; 052002 -- Nuclear Fuels-- Waste Disposal & Storage; 510500 -- Environment, Terrestrial-- Site Resource & Use Studies-- (-1989)