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-6- I I I I I I I I I I I I I I I I I I I explain the differences shown in table 1. FOr the national assessment, two estimates were developed: (1) the state-regional future (SRF) and (2) the National Future (NF). The NF estimates were developed by Federal agencies, primarily the Geological Survey and the U.S. Water Resources Council. The SRF estimates were prepared mainly by the 10 basin States. Two reference points on the Missouri River main stern are most often used to summarize water data in the Missouri Basin--Sioux City, Iowa, and the mouth of the Missouri River near St. Louis, Missouri. In table 1, the cumulative amounts for the Eastern Dakotas and Lower Missouri subbasins correspond respectively to these reference points. Table 1 shows the framework study estimate for current net depletions above Sioux City (Eastern Dakotas) is 6,436,000 acre-feet per year as compared to 9,732,000 acre-feet per year estimated in the SRF. Estimates of current average annual flow at Sioux City in the framework study and the SRF are 20,596,000 and 18,458,000 acre-feet, respectively. At the mouth, net annual depletions were estimated in the framework study to be 11,698,000 acre-feet, and the annual outflow from the basin was estimated to be 53,885,000 acre-feet. The SRF estimates are 15,498,000 and 49,362,000 acre-feet, respectively. Beyond these main stern discrepancies, estimates along individual tributaries resulting from the two sources differ by as much as 100 percent. Differences in water use and availability estimates are statistically significant and are caused primarily by differences in estimated irrigated acreage and estimated unit water consumption for irrigation from surface and ground water sources. These differences among estimates of water availability and depletions seriously inhibit the ability to accurately determine impacts that future management alternatives would have on the basin's water and related land