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compiling surface water data on the daily inflows and outflows for specified river or stream <br />reaches, and then applying a set of steps to convert the daily flows into estimates of monthly <br />gains or losses between the surface water system and the hydrologically-connected aquifer <br />system. The gain/loss results, referred to as baseflow, are an important part of the water <br />balance of flee South Platte River system. The baseflow results will be used >ln helping <br />calibration the alluvial groundwater flow model being developed under Task 48. <br />The following table summarizes the sections contained in finis TM. <br />Section Descri tion <br />1.0 Investigation Area and Data Collection <br />1.1 Areas of Investi ation <br />12 Data Collection <br />2.0 Methodolo <br />2.1 Mass Balance Determination <br />2.2 Short-Term AveraQin~ <br />2.3 Constraint Determination <br />2.4 Lon -Term Avera~in~ <br />3.0 Results and Anal sis <br />4.0 Sunnmar and Conclusions <br />5.0 Reconmlendations <br />6.0 Peferences <br /> Appendices <br />A Mass Balance Components <br />B Command Files <br />C Monthl Mass Balance Approach <br />D Constraint Values <br />1.0 Investigation Area and Data Collection <br />Stream ga>ln or loss is def>lned in finis TM as the recharge from or discharge to the alluvial <br />aquifer that is in hydrologic conmlunication wifln the overlying stream system, respectively. <br />The flow un a stream that is due to groundwater discharge is commonly referred to as baseflow. <br />This task was initiated to complement sinnilar work performed recently (and not yet published) <br />by the United States Geological Survey (USGS) on a limited portion of the main stem of the <br />South Platte River from Denver to the Kersey gage near Greeley. The results of this task will be <br />used to help calibrate the alluvial groundwater model being developed under Task 48 by <br />cotnpar>ing the estimated gain/loss from this Task and fine model-simulated gauz/loss in a given <br />reach and time period. In addition, the results of this task will provide a useful addition to the <br />understanding of tlne Soutln Platte River surface water -groundwater system. <br />1.1 Areas of Investigation <br />Stream gain/loss estimates were determined for seven reaches along the South Platte P`iver and <br />two tributaries located withun tlne study area. Tlne reaches were defined using stream gages <br />SPDSS Phase 4 Task 46 Technical Memorandum -Final <br />0~4i 10i0~ <br />