Irrigation Water Demand Estimates for the Texas Panhandle (Region A)
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abstract
Severe drought conditions occurred in Texas during the 1990's and resulted in many water entities being forced to implement rationing programs to balance water demand with available supplies. Subsequently, the 75th Texas Legislature mandated a review of the State's Water Plan. As irrigation is the largest user of water in the Texas Panhandle, a critical assessment of irrigation water demand estimates was needed. Previously, the Texas Water Department Board (TWDB) had provided these projections, principally through surveys from county and regional Natural Resource Conservation Service (NRCS) personnel. To attain a more localized focus, the state was divided into 16 regions. Each region was charged to review the TWDB estimates, and either accept their statistics or formulate a methodology that would possibly be more realistic in reflecting the irrigation water demands in their region. The Texas Panhandle High Plains area was designated as Region A. It was comprised of the following 21 counties: Armstrong, Carson, Childress, Collingsworth, Dallam, Donley, Gray, Hall, Hansford, Hartley, Hemphill, Hutchinson, Lipscomb, Moore, Ochiltree, Oldham, Potter, Randall, Roberts, Sherman and Wheeler. In the past, large differences existed between the TWDB estimates and the measured drawdown in wells within the Texas Panhandle region. The alternative methodology proposed by the team and developed for Region A used calibrated crop evapotranspiration (ET) in estimating irrigation water demands for corn, cotton, grain sorghum, hay, pasture, peanuts, soybeans and wheat. Computations were based on the following: 1. Crop ET. Actual crop ET was derived from the large monolithic lysimeter facility at Bushland and obtained through the North Plains Potential Evapotranspiration Network (NPPET). 2. Monthly Effective Rainfall. A modified monthly effective rainfall was utilized from the procedure described in the NRCS National Engineering Handbook (Part 623, Chapter 2). 3. Percent Potential Evapotranspiration (PET). The percent crop PET utilized in Region A was based on Texas Agricultural Extension Service data gathered from actual producers' fields throughout the season by Agri-Partners and agency agricultural engineers. 4. Soil Moisture. Soil moisture level in the soil, which is utilized by the plant during the growing season. 5. Crop Hectares. Crop hectares used were from the Texas Agricultural Statistics Service and Census of Agriculture. A simulation utilizing the alternative methodology resulted in a relatively accurate estimate of irrigation demand in the region for the base year 1997. Irrigation demand estimates resulted in groundwater depletion within 97% of what was observed in test wells in the region. The proposed methodology appears to be considerably more accurate then the previous survey-based approach. Copyright 2004 ASCE.
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Watershed Management and Operations Management 2000
