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:. ~ . ~~ ~ December 4, 1979 Page 2 River will flow on two sides of the pit within an average dis- tance of 100 feet. The evaporation loss from the new gravel pit's water surface will cause a new loss to the hydrologic balance of the area, which includes the South Platte River. The loss of streamflow resulting from the lake evaporation will average at least 300 acre-feet per year. The reduced streamflow will cause injury to senior vested water rights since the South Platte River is highly over-appropriated and sufficient vrater is not available for existing water rights. For example, the reduction in streamflow in this short reach of the river resulting from the evaporation from 141 acres could exceed 1.5 cfs during the months of July and August (SCS National Engineering Handbook, 1961). The loss of 1.5 cfs in this particular area is especially injurious since the nunber of very senior water rights is significant with many priority dates in the early 1660's. It is very common for a call from one of these water rights to exist throughout the critical part of the irrigation season, i.e., July through September. These direct flow crater rights have decreed amounts varying from 4.0 cfs to 177.0 cfs with the majority less than 40.0 cfs. It is quite clear that a loss of 1.5 cfs at this time of year to these water rights is significant and cannot be tolerated. P1ore importantly, if these water rights have to place a call more often or for a greater amount, it has serious consequences upstream on junior water rights. The senior o-rater rights will call more water do;an through South Park and Denver and will reduce the amount of water normally available for diversion by water users upstream. A loss of 1.5 cfs is significant to a city such as Denver or Aurora who divert from the South Platte River. For a comparison, 1.5 cfs is equivalent to 1,039,260 gallons per day, which is a con- siderable amount of water, especially to a city. 4. We realize that the argument is often presented that it is up to the State Ehgineer's Office to take whatever steps are necessary to protect other water rights. However, we want to stress that once the gravel pit lake is constructed in accor- dance with a permit granted by the Board and the naturally occurring process of evaporation begins, there is no statute that this office can use to prevent the stream depletion since there is no diversion or storage of water through an act of man. This is the reason why we feel that it is the Board's responsibility to insure that the impacts upon the hydrologic balance as a result of mining and reclamation are minimized. JAD/HDS/pjl a eris A. Danielson cc: Jim Clark, Div. Eng. Consolidated Ditches of District 2