Water-level altitudes, spring and fall 1981 and spring 1982, for observation wells in the study area........... Average annual streamflow and average October through December streamflow for gaging stations in or near the s tudy area.

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Texas, is a region of great hydrologic diversity. This study examines the relationships between climate, vegetation, and soil that affect consumptive water use and recharge to the groundwater system. Computations of potential recharge and consumptive water use were restricted to those areas where the aquifers under consideration were the immediate underlying system-. The principal method of analysis utilizes a soil-moisture computer model. This model requires four types of input: (1) Hydrologic properties of the soils, (2) vegetation types, (3) monthly precipitation, and (4) computed monthly potential evapotranspiration (PET) values. The PET simulation is based on the Jensen-Haise method, which requires monthly solar radiation and temperature data. Results of the soil-moisture program, which add the affects of vegetation and the hydrologic characteristics of the soil to computed PET values, confirm the significant regional differences in consumptive water use or actual evapotranspiration (AET) and potential groundwater recharge. Under two different vegetative conditions-the 1978 conditions and pre-agricultural conditions consisting of only grassland and woodlandoverall differences in recharge were minimal. Recharge values were significantly different from pre-agricultural conditions only in selected areas where tame hay (principally alfalfa) or fallow acreages were appreciable. Mean annual recharge under both conditions averaged slightly more than 4.5 inches for the entire study area, but ranged from less than 0.10 inch in eastern Colorado to slightly more than 15 inches in Arkansas. Patterns of annual recharge closely paralleled yearly and cool season precipitation (October through March). It was concluded that climatic effects dominated overall regional recharge patterns in the study area, with local variations resulting from differences in vegetation and soil.

Plate 2 -Projected water-level declines by 2000 and 2020 assuming no new irrigation development after 1980. A. Projected declines by May 31, 2000, if application rate _ _ equals 80 percent of consumptive-irrigation requirements. B. Projected declines by May 31, 2000, if application rate exceeds consumptive-irrigation requirements--13.75 inches in Buffalo County and eastward and 10.0 inches in Uawson and Custer Counties. C. Projected declines by May 31, 2000, if application rate equals consumptive-irrigation requirements. D. Projected declines by May 31, 2020, if application rate equals consumptive-irrigation requirements. Plate 3 -Projected water-level declines by 2000 and 2020 for different rates of irrigation development and water application. A. Projected declines by May 31, 2000, if rate of development is 2 percent and application rate is either 80 or 120 percent of consumptive-irrigation requirements. B. Projected declines by May 31, 2000, if rate of development is 2 percent and application rate equals consumptiveirrigation requirements. C. Projected declines by May 31, 2000, if rate of development is 5 percent and application rate is either 80 or 120 percent of consumptive-irrigation requirements. D. Projected declines by May 31, 2000, if rate of development is 5 percent and application rate equals consumptiveirrigation requirements. E. Projected declines by May 31, 2000, if rate of development is 8 percent and application rate is either 80 or 120 percent of consumptive-irrigation requirements. F. Projected declines by May 31, 2000, if rate of development is 8 percent and application rate equals consumptiveirrigation requirements. G. Projected declines by May 31, 2020, if rate of development is 2 percent and application rate equals consumptiveirrigation requirements. H. Projected declines by May 31, 2020, if rate of development is 8 percent and application rate equals consumptiveirrigation requirements.

No abstract