| OCR Text |
Show or average depletion for any period of .approximately constant acreage irrigated, V = the probable virgin flow of the stream for the given year, and Vm ~ the average virgin flow. This variation of consumptive uses of water depending on fluctuations in the available annual supply, is, however, insufficient for adequate compensation of the discrepancies between the theoretical and observed outflow quantities. It is indicated in the report of Mr. Blaney and Mr. Criddle, which is Appendix B of the Final Report of the Engineering Advisory Committee to the Upper Colorado River Basin Compact Commission, that actual consumptive use rates of irrigation water are reduced by reason of precipitation during the growing season. Summer precipitation must, therefore, be one of the causes of deviations from the average trend in the relations between inflow and outflow on any drainage basin. Although temperature variations during the growing season may also have a material effect in causing these deviations from average conditions, the relation indicated in formula (2), below, does not take such variations into account. Preliminary trials using summer precipitation indicated that further improvement of the inflow-outflow equation could be secured by the use of this factor. The best relationship thus far obtained in this investigation is given by the following formula (2) - Y = 2.5086X2 - 239.5(1 + 0.576-^--) + 14.88X5 - 733 In this equation, Y is the theoretical outflow .and X2 the inflow index as in formula (1), M2 is the average of the inflow index and X5 is the amount of the summer precipitation in inches of depth. The term in parentheses is the factor indicating the amount of variation to be applied to correct the .average depletion of 239,000 acre feet for variations in the available water supply. With this equation, the standard error is reduced by some 10,000 acre feet while the square of the coefficient of correlation is increased in about the same proportion. The solid diagonal line and the dots on the accompanying Plate show the average trend in the relation between the inflow index and outflow quantities, arrived at through the application of the simple linear correlation provided by formula (1). The open circles show the relation as determined by formula (2). It is evident that in most cases the circles fall nearer the theoretical line than before, although in a few cases the reverse is true. This indicates that certain causes of variations have not been accounted for by the variables included in formula (2). In addition to the introduction of variations in irrigation, consumptive uses and the effect of summer precipitation, other causes of variations in outflow will be investigated including summer -61- |
