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river will have a lower and later peak value of stream accretion. The timing of accretions <br /> to the river is a crucial component to understanding which recharge sites will have the <br /> highest benefit to the overall recharge program. <br /> A Cursory Evaluation of Recharge Structures <br /> The ten proposed recharge sites were evaluated in the SDF View computer model. The <br /> results of this evaluation are found in Appendix A. Overall, the results indicate that: (1) of <br /> the proposed recharge pond sites, those with higher SDF values or that are further away <br /> from the river are priority sites, (2) initial operation of a recharge project will require <br /> larger amounts of annual recharge than would be expected in the long-term, and (3) <br /> pond capacity determination is a function of many variables and is therefore somewhat <br /> subjective. <br /> 1. The primary reason the Union Ditch plans to develop a recharge project is to <br /> replace depletions in the river that are caused by well pumping. The most critical <br /> time for replacing depletions is when water demand is high or when there is a call <br /> on the river (typically during the late summer months). The operation of recharge <br /> structures should provide adequate replacement water during these times. <br /> The results show that the Mercure (SDF 480 days) and R. Alles (SDF 480 days) <br /> sites are priority recharge sites, because they provide the most recharge during <br /> the critical times (Figure 3)2. Although sites very close to the river do not appear <br /> to be as important as those that are far from the river, it is believed that a large <br /> range of SDF values will provide a degree of flexibility in recharge operations. <br /> 2. Figure 4 demonstrates stream accretion that is expected from continual recharge <br /> at a recharge site with a SDF of 480 days. During initial recharge operation, it is <br /> expected that excess recharge water will be needed to "charge" up the system. <br /> Annual recharge quantities are expected to be less in future years, as the <br /> residual effects of previous years' recharge accrue in the river. Over the long- <br /> term, annual stream accretion will approach annual recharge. <br /> 3. In theory, the pond capacity needed to recharge a specific amount of water can <br /> be determined from the infiltration characteristics of the soil and the flow rate of <br /> water that is available for recharge. Unfortunately, these factors may not be <br /> known prior to recharge pond excavation and operation. Thus, the capacity of a <br /> recharge pond cannot specifically be determined and in practice will more than <br /> likely be a function of the site constraints and economic feasibility of the project. <br /> 'Because the Union Ditch will be used for irrigation from April through November,recharge will most likely occur between <br /> December and March. If February and March are the last possible times for recharge during any given year,for example, <br /> then large SDF values are more desirable because they produce a later peak in accretions and provide the most water to <br /> the river during critical months(August and September). If it is possible to recharge later into the spring,such as in April or <br /> May,a lower SDF value may be adequate. <br /> Aqua Engineering, Inc. Recharge Project Potential <br /> February 17, 2004 - 6 - <br />