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SPDSS_Task46-2_StreamGainLossEstimates
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Last modified
4/17/2013 9:26:27 AM
Creation date
6/11/2008 1:49:45 PM
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Decision Support Systems
Title
SPDSS Task 46.2 - Stream Gain/Loss Estimates - Phase 4
Description
This Technical Memorandum summarizes the compilation and analysis of data for the computation of monthly gains and losses for the main stem of the South Platte River and selected tributaries for the study period of 1950-2005.
Decision Support - Doc Type
Task Memorandum
Date
4/10/2008
DSS Category
Groundwater
DSS
South Platte
Basin
South Platte
Contract/PO #
C153953
Grant Type
Non-Reimbursable
Bill Number
SB01-157, HB02-1152, SB03-110, HB04-1221, SB05-084, HB06-1313, SB07-122
Prepared By
CDM
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3.0 Results <br />The estimated monthly gain/loss values for each reach are summarized below and are <br />displayed graphically in a series of hydrograplls. Average annual baseflow and associated <br />mass balance values for t11e study period (1950 to 2005) are shown for each reach in Fib res 3 <br />through 11. Average monthly baseflow and mass balance values for 1991 through 1994 for each <br />reach >11 Fibres 12 through 20. This is the steady-state calibration period t11at will be used in <br />t11e alluvial groundwater flow model being developed under Task 48. The average monthly <br />values are also presented as gain/loss per river Hole in Fibres 21 through 30. The time series of <br />monthly baseflow results corresponding to the transient model calibration period (1999 through <br />2005) are presented for each reach in Fibres 31 through 39. Each set of graphs (average annual, <br />average monthly 1991-1994, average monthly 1991-1994 per river nine, and average mont111y <br />1999-2005) include the same range on t11e axes to facilitate comparison between reaches. <br />Positive flows shown on all b apps represent gaining stream conditions and negative flows <br />represent losing stream conditions. Flow values may not transition smoot111y between adjacent <br />reaches since the values represent the average baseflow over the entire reach. The baseflow <br />values show much smoother trends than the mass balance values due to t11e data processing <br />steps associated with the Pilot Point method. The difference between the baseflow and mass <br />balance curves represent other flows that are not quantified. <br />Data files developed to estimate stream gain/loss have been provided to the State wit11 the F>11a1 <br />TM, under separate cover. The monthly average baseflow data presented in Fibres 12 through <br />20 and Figures 31-39 will be used to help qualitatively calibrate the steady state and transient <br />alluvial groundwater models, respectively, by comparing the computed to simulated <br />grotmdwater gain/loss in a given reach and tinge period. In addition, the results of this task <br />will provide a useful addition to the tulderstanding of the South Platte River surface water - <br />grotuldwater system. <br />The average annual baseflow results are generally positive for the seven Sout11 Platte reaches <br />and the two tributary reaches, indicating that an arulual basis these rivers are gaining flow from <br />the alluvial aquifer. Table 8 summarizes the average mass balance and estimated baseflow from <br />each reach for the full period of record. Tl1e column labeled Other Gaul-Loss represents the <br />difference between the mass balance and estimated baseflow values. The hig11 values for the <br />South Platte 7 - Balzac to Julesburg reach (Table 8) is likely due to the relatively long length of <br />this reach (98 nines) compared to the other reaches. The South Platte 4 -Fort Lupton to Kersey <br />reach also shows high values but is not long at 39 miles. The higher baseflow values >11 this <br />reach may be related to a relatively large amount of surface water-based irrigation u1 this area <br />that would provide return flow water as baseflow. The negative mass balance value for t11e <br />South Platte 5 -Kersey to Weldona reach (Table 8) demonstrates the effect of a few very low <br />annual values that are dampened out in t11e associated baseflow value for this reach. <br />SPDSS Phase 4 Task 46 Technical Memorandum -Final 14 <br />0~4i 10i0~ <br />
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