The volume and areal distribution of ground-water withdrawals (pumpage) for irrigation during 1980 are required for the High Plains Regional Aquifer-System Analysis. In 1979, approaches and instrumentation that might be suitable for application to 1980 water-use determinations were tested. Pumpage was sampled by monitoring time of operation and discharge of irrigation wells during the growing season. The total volume pumped during the irrigation season was compared to the crop type and acreage irrigated. This comparison provided a means of extending sampled pumpage information to unmonitored areas using irrigated cropland maps. A transient-time flowmeter and a vibration-sensitive timing device proved to be reliable in providing discharge and time of operation information, respectively. Statistical analysis of comparisons between pumpage and irrigated cropland indicated that significant differences existed in the amounts of water applied between flood and sprinkler irrigation systems. However, statistical analyses of differences in amounts of water applied for different crop types and for selected climatic factors were inconclusive. A variety of approaches were tested to develop the irrigated cropland maps needed to extend sampled pumpage data. Of the methods tested, only Landsat data proved to be effective for application to an area as large as the High Plains. The results obtained in the 1979 evaluation of instrumentation and pumpage sampling approaches have been used to formulate a strategy for monitoring irrigation water use in the High Plains in 1980. (USGS)
