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SPDSS Memorandum <br />Final <br />To: Ray Alvarado and Ray Bennett <br />From: LRE -Erin Wilson and Greg Espegren <br />Subject: Task 69 -Estimate Reservoir and Stock Pond Evaporation <br />Date: November 13, 2006 <br />Introduction <br />Reservoir evaporation is a source of consumptive use in the SPDSS study area. In Phase I and II <br />(Task 5), key reservoirs and reservoir systems were identified and available records of their end- <br />of-month storage contents were documented for the 1950 through 2003 period. The purpose of <br />Task 69 is to estimate the capacity of smaller, non-key reservoirs and stock ponds, combine them <br />by Water District into "aggregated" reservoirs, and estimate their evaporative losses. Key and <br />aggregated reservoirs and stock ponds will be included in future surface water modeling efforts <br />to represent diversions to storage, reservoir use, and evaporation. Evaporation estimates are <br />components of the SPDSS Consumptive Uses and Losses Summary and the Water Budget <br />models. As defined in the scope, the Task 69 objective is to: <br />Aggregate non-key reservoirs and stock ponds and estimate basin-wide evaporation for <br />the SPDSS Consumptive Use and Losses Report, Water Budget, and surface water <br />modeling efforts, using both GIS and HydroBase data. Compare the two approaches, <br />recommend a final approach, and develop reservoir and stock pond evaporation for the <br />SPDSS study period. <br />In previous CDSS efforts, reservoir evaporation was estimated using basin-wide decreed storage <br />capacity extracted from HydroBase. Although there are gravel mining operations in other CDSS <br />basins, there are areas along the South Platte River and its major tributaries where gravel mining <br />operations are significant. Many of the gravel pits constructed prior to 1981 do not have decreed <br />storage rights, and therefore, may not be identified through information available in HydroBase. <br />Therefore for SPDSS, both GIS and HydroBase approaches were applied, results compared, and <br />a final approach recommended. <br />In addition, a recommendation was made for locating the aggregate reservoirs and stock ponds in <br />the model network for future surface water modeling efforts. <br />GIS Reservoir Area -Approach and Results <br />The SPDSS Spatial contractor, RTi, recently developed an ArcGIS shapefile of water bodies in <br />the SPDSS study area. The shapefile was created from 2001 satellite imagery and digital <br />orthoquads and generally include reservoirs with surface areas of three acres or more, based on <br />imagery resolution restrictions. Several satellite snapshots were used and the water bodies are <br />Page 1 of 14 <br />