PROJ00048 - Laserfiche WebLink

Home Browse Search

f i represents the volume available for storage during the period of time when irrigation demands are not being met. The graph shows that, on an average year, 1906 acre-feet of water would be available for storage between the first week of August through the first week of May. A similar analysis, using dry year flow data, resulted in a total of 1041 acre-feet of storage available from the middle of August through the middle of April. , ..i ,"'J .' ] :"'"J '.~ The above method may overestimate storage avail- ability because it does not consider the reduced flows available at the upstream dam site. It may underesti- mate storage availability because it does not consider the increased streamflows available to satisfy ,the diversion requirements at the downstream headgate locations. Another more detailed method, which would also predict reservoir operation needs, was used to estimate storage availability. This method uses the 1980 middle fork of Arapahoe Creek streamflow data in conjunction with the diversion schedule. It may overestimate the supply since 1980 was a high winter runoff year. This is compensated for by the very low 1980 summer precipitation. In addition, very conser- vative estimates of the flow rates expected at the diversion sites were made in this analysis. The first step of this analysis was to adjust the daily streamflows expected at the dam site and the ditch headgate locations--based on the ratio of the drainage areas at each of these collection and diver- sion points to the drainage area of the gaging sta- tion. Secondly, the diversion amounts presented in Table IV were subtracted from the daily streamflows. The resulting daily flows showed when deficit stream- flow would occur at the lower headgates (i. e. storage water would need to be released) and when water ex- ceeding the diversion requirement would be available for storage. The summation of flow rates at the dam site when water was available for storage showed 2,259 acre-feet would be available throughout the water year. Of this, 375 acre-feet was runoff in excess of the di- version requirements stored during May and June; 1884 acre-feet would be available from August 1 through April 24. (See Appendix D for computations.) Both of the methods of estimating storage availab- ility show that the 1802 acre-feet project water re- quirement should be met in most years through the storage of water by the proposed Hyannis Reservoir. Because increased flows at the diversion sites were either ignored or pessimistically estimated, we would expect more of the runoff to be available for diversion than is reflected in either analysis. Thus, adequate water should be available in all but the driest years to fill the reservoir. -1.9-