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SPDSS Phase 4 Task 46.2 <br />Stream Gain/Loss Estimates Technical Memorandum <br />FINAL <br />To: Ray Alvarado <br />From: Camp Dresser and McKee h1c. <br />Jessica Gilliam, Jordan D>17uck, and Gordon McCurry <br />Subject: SPDSS Groundwater Component Phase 4 Task 46.2 Final <br />Stream Gain/Loss Estimates Technical Memorandum <br />Date: April 10, 2008 <br />Introduction <br />The groundwater component of the South Platte Decision Support System (SPDSS) focuses on <br />compiling and evaluating available relevant data to support the Decision Support System (DSS) <br />for the South Platte River watershed and to add the data to HydroBase, the State of Colorado's <br />1lydrological database. T11e SPDSS study area is presented in Figure 1. For the purposes of the <br />SPDSS, the grouundwater study area is divided into two hydrologic regions. The Denver Basin <br />Region includes the bedrock aquifers of t11e Denver Basin. T11e Sout11 Platte Alluvium Region <br />consists of fl1e unconsolidated deposits of t11e Soufl1 Platte River mainstem, extending <br />downstream from just below Chatfield Reservoir to the Nebraska state line at Julesburg. Tl1e <br />South Platte Alluvium Region also includes the alluvium overlying the Denver Basin bedrock <br />aquifers >11 Water Divisions 1 and 2. <br />This task was undertaken for t11e Colorado Water Conservation Board (CWCB) and Division of <br />Water Resources (DWR), under Task 46 of Phase 4 of t11e SPDSS by Camp Dresser & McKee <br />(CDM). Task 46 of the SPDSS includes the collection and analysis of existing data on stream <br />inflows and outflows >11 fl1e main stem of the South Platte River and selected tributaries to <br />characterize stream gains and losses in each reach. The objectives of this task are as follows: <br />To develop estimates of stream gains and losses from groundwater in the main stem of the South <br />Platy River and its tributaries within the study area to be used to help calibrate the alluvial <br />groundwater model being developed under' Task -18. <br />This Technical Memorandum (TM) summarizes the compilation and analysis of data for the <br />computation of monthly gains and losses for the maul stem of the South Platte River and <br />selected tributaries for the study period of 1950-2005. <br />Approach <br />Gains and losses to the key rivers and streams in the study area were estimated using a process <br />developed by the State for the Rio Grande and Republican Rivers. This process involves <br />SPDSS Phase 4 Task 46 Technical Memorandum -Final <br />0~4i 10i0~ <br />