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accompanying curve superimposed on the computed mass balance for fl1e reach. The pilot <br />points were manually manipulated using professional judgment to produce a curve that best <br />approximated baseflows in the reach. During the development of the Rio Grande Decision <br />Support System groundwater model, the original Pilot Point method was enhanced. In an <br />attempt to reduce the effects of subjectivity involved in this approach, an automated <br />spreadsheet version was created for the Rio Grande and applied to the South Platte 1lerein that <br />nunucked the results from the manual method of manipulatuzg the data yet makes the results of <br />baseflow analysis more reproducible. <br />The Pilot Point method as applied in this task estimates monthly baseflow values using fl1e <br />following process for each reach: <br />1. daily inflows and outflows are used to compute a daily mass balance <br />2. a short-term moving average is applied to the daily mass balance to account for stream <br />lagging, <br />3. fl1e lagged daily values are constra>11ed to reflect the maximum gains and losses <br />expected for the reach, and <br />4. a longer-term moving average is applied to the constrained and lagged values to <br />estimate mont111y baseflows. <br />The mass balance discussed in the first two steps refers to the difference in daily inflows and <br />outflows described in Section 1. The baseflow, described >11 the final step, differs from the mass <br />balance due to the processing steps that comprise the Pilot Point method. Details regarding fl1e <br />various processes involved with the Pilot Point method are discussed uz the remainder of this <br />section. <br />2.1 Daily Mass Balance Determination <br />All inflow and outflow data described in Section 1.2 was added to a spreadsheet and applied in <br />a mass balance equation to estimate baseflow for eac11 day within the period 1950 to 2005. The <br />mass balance was developed by subtracting all of fl1e inflows and add>11g all of the outflows to <br />the flow values from the downstream gage for eac11 reach. The sources of these flow data are <br />described in Section 1.2. <br />Inflows used in the mass balance calculation include the following: <br />• the flow of the upstream gage defining the reach, <br />• streamflows from tributaries, <br />• industrial and municipal discharges, and <br />• reservoir releases. <br />Outflows used in fl1e mass balance calculation include fl1e following: <br />• key diversions <br />• aggregate diversions <br />• fl1e flow of t11e gage at fl1e do~nmstream end of fl1e reach <br />2.2 Short-Term Averaging <br />The graphed results of $Ze daily mass balance calculated for each reach displayed large swings <br />in values, from high positive to negative values and back. These wide daily variations are <br />SPDSS Phase 4 Task 46 Technical Memorandum -Final <br />0~4i 10i0~ <br />