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SPDSS Memorandum <br />Final <br />To: Ray Alvarado and Ray Bennett <br />From: LRE -Erin Wilson, Beorn Courtney, and James Heath <br />Subject: Task 64 -Review and Develop Precipitation Recharge Estimates <br />Date: May 11, 2007 <br />Introduction <br />Average annual precipitation varies across the South Platte River basin from 30 inches or more <br />along the Continental Divide down to 7 to 15 inches across the plains east of Denver and in the <br />South Park area in the southwest part of the basin. Total precipitation can be consumed by <br />irrigated and native vegetation, captured in surface water storage and then evaporated, held in <br />soil zone storage, produce surface water runoff to local drainages, or recharge the aquifer (i.e. <br />deep percolation). Precipitation recharge to the aquifers is an inflow component to the Denver <br />Basin and South Platte Alluvial ground water models (Figure 1). It is important that <br />precipitation recharge estimates are reasonable and consistent with estimates of other uses of <br />precipitation considered in the model. <br />This memorandum presents the general approach for Task 64: <br />1. Review published information for the basin and western United States on precipitation <br />recharge to ground water aquifers. <br />2. Recommend an approach to estimate precipitation recharge that is reasonable and <br />consistent and integrated with other uses of precipitation (e.g. precipitation use by <br />irrigated crops, precipitation use by native species, etc.). <br />3. Develop monthly precipitation recharge estimates for both the Denver Basin and South <br />Platte alluvial ground water models for the SPDSS study period based on key climate <br />stations and their spatial distribution determined in Phase 1, Task 53. <br />Task 64.doc 1 of 13 <br />