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I I I I I I I I I I I I I I I I miles. Assuming that water is diverted during the winter months (December-February), and an average SDF of 100 days is used, the majority of the water which was placed into the alluvium through natural seepage or through the use of recharge ponds, would be realized at the South Platte River during the spring runoff period (March-June). Recharge to the river during the spring runoff period, contributes very little towards the goals of this project. Recharge reservoirs require the maintenance of the bottom interface with the alluvium to insure maximum percolation. Silty water will tend to plug the voids which requires occasional scarification of bottom and removal of fines. This is less of a problem with pumped groundwater than ditch water. The possibility of using the site as strictly a groundwater recharge project seems to be of limited benefit. The timing of the return flows to the South Platte River will not provide the maximum benefit in removing or preventing a call placed on the river. It is felt that the northern portion of the site could be effectively utilized for a smaller recharge pond. Water could be diverted into the recharge portion of the project when it was available during the spring runoff period. This area could be developed into wetlands mitigation for the proposed reservoir. Diverting water into this site during the spring runoff period would allow for flows to accrue to the river during the late summer months. The limitation of utilizing a portion of the site for a recharge pond would be the availability of capacity in the Peterson Ditch. Peterson Ditch shareholders may be diverting flows during the spring runoff period, which could limit the amount of water available for recharge. Table 3 is a summary representation of four different scenarios for the operation of a recharge pond. The different operating scenarios represent two periods of diversion into the recharge area (Jan/Feb & May/June) and are evaluated for SDF's of 100 and 200 days. Recharging during the spring runoff (May/June) appears to have the greatest benefit towards achieving the project goal of increasing the flows in the river in the late summer months. The location of the recharge area, within the project site, is capable of achieving SDF's ranging from 100 to 200 days. The variation in the SDF does change the proportion ofthe recharged water that is returned to the stream during each individual month, but does not seem do have a drastic affect on the overall accretions back to the river during the latter parts of the irrigation season. Diverting water for recharge during the spring runoff period could return approximately 40% of the quantity recharged back to the South Platte River during the late summer period. The possibility of developing a portion of the site into a recharge project does seem to be feasible and beneficial towards achieving project goals. Additional study would be recommended to compare the effectiveness of recharge against development of additional reservoir storage. Table 3 Summary of Accretions to South Platte River from Recharae at eservoir S te Rechan e Period Accretion To South Platte RIver 'Effective Stream Recharae ~tream Depletion Fact, January February May June July August September October Stream Accretions! 1# of Davsl I lacre-feetl lacre-feetl facre-feetl facre-feetl Ilacre-feetl lacre-feetl lacre-feetl Ilacre-feet Recharae 100 500 500 0 0 34.9 27.6 22.6 18.9 10.4% 100 0 0 500 500 168.5 100.7 64.7 46.0 38.0% 200 500 500 0 0 42.3 34.3 28.6 24.3 13.0% 200 0 0 500 500 115.2 97.1 71.0 53.7 33.7% R . Effective Stream Recharge is defined as the percent of recharge water that a=ue to the stream during the late summer months (July-October) I I I All reservoirs will have a certain amount of natural seepage associated with normal operations. The seepage will be dependent upon the native soils and the type of liner system that is constructed. Depending upon what method of sealing the reservoir is opted for, consideration should be given to attaining credit for the groundwater recharge and eventual stream accretion associated with the seepage. See Appendix B for detailed calculations used in Table 3. 12