PROBLEMS FROM DEVELOPMENT 155 



miles of the Platte River Valley, and annual pumpage is 

 estimated to be of the order of 350,000 acre-feet. Some wells 

 near the channel pump water replenished by infiltration 

 from the stream. Others pump water replenished by pre- 

 cipitation, but the pumpage nevertheless draws water that 

 would otherwise move toward the stream and contribute to 

 its flow. For many wells the natural supplies have been aug- 

 mented by the downward percolation of irrigation water 

 that was diverted from the stream. 



Water-table contours for 1929 suggest that ground water 

 left the watercourse between Kearney and Grand Island and 

 moved south-eastward toward the drainage basin of the Blue 

 River or the Republican River. Maps based on data col- 

 lected in October 1948 78 shows that water losses from the 

 main supply canal and from Johnson Reservoir of the Cen- 

 tral Nebraska Public Power and Irrigation District, together 

 with seepage losses from water applied to agricultural lands 

 in the district's Tri-County area, have since 1929 created 

 a definite ground-water divide beneath the upland area 

 south of the valley so that there is now less possibility of 

 escape of ground water from the valley. However, only a 

 fraction of the water percolating downward from the irri- 

 gated areas on the upland south of the valley returns to the 

 Platte watercourse. The rest, on the south side of the ground- 

 water divide, escapes from the Platte drainage basin. Seep- 

 age losses from the main supply canal and from Johnson 

 Reservoir are estimated to be of the order of 190,000 acre- 

 feet a year, but the amount of ground water that leaves the 

 watercourse is unknown. 



Ground-water storage in the watercourse is sufficient to 

 cushion the effects of alternating dry and wet climatic cycles. 

 During the dry 1930's, pumping draft was greater than re- 

 plenishment, and water levels declined in almost all parts 



78 Part of a report based on cooperative ground-water investigations by 

 the U.S. Geological Survey and the Conservation and Survey Division of the 

 University of Nebraska, in preparation for publication in the near future by 

 the Conservation and Survey Division. 



