OCR Text |
Show Discharge.- Ground water is discharged from the unconsolidated deposits in Heber Valley by pumping from wells, by evapotranspiration, by effluent seepage, and probably by subsurface outflow through the surrounding consolidated rocks. The total volume of water pumped from wells in the valley is very small, and there have been no drastic changes in irrigation practice for many years; hence the long- term recharge- discharge regimen is fairly stable and should be in balance. The average annual discharge, therefore, should be about 86,000 acre- feet per year. The total evapotranspiration from Heber Valley, calculated by the Blaney- Criddle method ( Blaney and Criddle, 1962) is about 81,000 acre- feet per year, ( evaporation from Deer Creek Reservoir is not included in this amount). Part of the evapotranspiration loss is the crop water requirement and is supplied by irrigation water and summer precipitation ( p. 28); and according to the assumption made on page 27, part of the loss will be supplied by the winter precipitation. The net evapotranspiration loss from the ground- water body, therefore, is calculated as follows: Acre- feet Total evapotranspiration 81,000 Less crop water requirement ( irrigation water and May- September precipitation) . - 43,000 Less October- April precipitation - 27,000 Net evapotranspiration loss of ground water 11,000 Ground- water discharge by effluent seepage includes the accretion to Deer Creek Reservoir ( 47,000 acre- feet per year, p. 8) and the discharge to the Provo River ( 11,000 acre- feet per year, p. 12). Ground- water discharge to the Provo River apparently occurs throughout the length of the river in the valley. The total discharge from the foregoing calculations is 69,000 acre- feet per year, or 17,000 acre- feet less than the average annual recharge. No direct evidence of subsurface discharge from the valley fill has been found, but this unbalance in the recharge- discharge calculation may indicate such subsurface discharge. Thus the average annual discharge, in acre- feet, from the unconsolidated deposits is: Net evapotranspiration loss 11,000 To Deer Creek Reservoir 47,000 To Provo River 11,000 , Subsurface outflow 17,000 Total discharge 86,000 |