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C00883 CHAPTER 1 THE CURRENT SITUATION INTRODUCTION The purpose ot this chapter is to describe, in a very general way, the physical situation with respect to surface water and groundwater in interstate river basins and interstate aquilers. It has been estimated that the average annual streamflow into the state is about one million acre feet, whereas the average annual outflow is about seven million acre feet.' This chapter is designed to give the reader a general idea of how and where that water is distributed in Nebraska. A summary of general topographic characteris- tics, average precipitation, high, low and average annual inflows and/or outflows on the major streams, and any legally established entitle- ments or obligations, whether by court decree or compact, has been included for each interstate stream basin in the state. There is relatively little information for inter- state groundwater aquifers underlying Nebraska. The expanding knowledge of ground- water in general, however, has also brought about an increased awareness of the interstate impacts associated with groundwater use by states sharing a common aquifer or interstate river basin. The ever-expanding use of ground- water, for irrigation and energy development among other uses, could bring increased pressure to bear on the groundwater resource as well. To date, there are no legal allocations of groundwater between Nebraska and neighbor- ing states. A third source of water which it may be possible to artificially "tap" is the atmosphere, through weather modification. Nebraska has had limited experience with weather modification activity but the legal framework and potential for it defi n- itely exist. SURFACE STREAMS White River. Hat Creek Basin Description. The White River and Hat Creek are located in the northwestern corner of the state. They originate in the Pine Ridge, a massive sandstone escarpment which forms a part of the northern boundary of the high plains, and flow northeastward into South Dakota. The White River begins in northern Sioux county near the Nebraska-Wyoming state line, and flowing north- eastward into South Dakota eventually empties into the Missouri River above Fort Randall Dam. Hat Creek heads in the northwestern part of Sioux county and flows northward into the Cheyenne River in South Dakota. The basin formed by these two streams is topographically marked with rugged steep slopes in the Pine Ridge area and a gently sloping area of clay hills and badlands forming narrow bottom lands to the north and west. The streams have cut deeply into the land and formed narrow valleys adding to the generally rough nature of the basin. The typical groundcover, ranging from conifer- ous trees in the Pine Ridge to native grasses in the badlands, the rugged topography, and clayey soils make cultivation impractical and difficult in most cases. Of a total land area of 1,360,000 acres,2 only about 26,600 acres were irrigated from surface water and 1,400 acres from ground- water as of 1975. The average annual precipitation is about 15 inches4 The runoff from precipitation is usually rapid because of the steep slopes and mostly impermeable soils. The one major reservoir in the region, Whitney Lake in Dawes County, is oper- ated by Whitney Irrigation District. It has a storage capacity of 10,960 acre-feet. 1-1