206 CONSERVATION OF GROUND WATER 



bly some water is rejected in the recharge area in most years. 

 The city has been able to increase its draft on the artesian 

 reservoir from 11,700 acre-feet in 1934 to 15,400 in 1948 

 without causing more than seasonal depletion of storage. 



Pine View Dam, completed by the Bureau of Reclama- 

 tion in 1936 in Ogden Canyon about a mile below Ogden 

 Valley, creates a reservoir with a capacity of about 45,000 

 acre-feet. This surface reservoir covers only a part of the ar- 

 tesian reservoir and is separated from it by the clay confining 

 layer that creates the artesian conditions. The weight of 

 water in the surface reservoir has compacted this clay and 

 probably reduced the upward leakage from the artesian res- 

 ervoir. At any rate, when the surface and artesian reservoirs 

 have been filled to capacity in recent years (both reach ca- 

 pacity approximately simultaneously), water levels in ob- 

 servation wells have been about 15 feet higher than the high- 

 est level reached before Pine View Dam was constructed. 

 The maximum discharge from the city's flowing wells has 

 increased from 22 to 33 cubic feet per second since the dam 

 was constructed. 



REGULATED FLOW 



Ground-water reservoirs recharged chiefly by streams com- 

 monly receive their greatest replenishment when the streams 

 are at high stage. Investigations in the intermontane valleys 

 of the West and in the watercourses in various parts of the 

 country have shown that the recharge is greater because the 

 fine materials are swept from the channel bed at high stages 

 and because the hydraulic gradient between the flood crest 

 and the adjacent ground-water reservoir is most favorable for 

 recharge. During periods of low flow the conditions may vary 

 widely from place to place: the entire flow of some streams 

 seeps into permeable materials of the channel except for small 

 losses by evapotranspiration; silt or clay dropped in the beds 

 of other streams may prevent seepage to the ground-water res- 

 ervoir; in other places the water table in adjacent alluvium 



