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Tests of Different Ways to Run CycleWell in the COHYST Western Model Unit. Prepared by Richard R. Luckey, High Plains Hydrology, LLC and Julie Gogoi, North Platte Natural Resources District. Outline. Description of CycleWell
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Tests of Different Waysto Run CycleWell in the COHYSTWestern Model Unit Prepared by Richard R. Luckey, High Plains Hydrology, LLC and Julie Gogoi, North Platte Natural Resources District
Outline • Description of CycleWell • Comparison of CycleWell results for 1 stress period using different pumping rates • Comparison of CycleWell results for 1 stress period using different injection rates • Comparison of CycleWell results for pumping well versus injection well for 1 stress period • Comparison of CycleWell results using 1 stress period versus using 100 stress periods • Conclusions throughout presentation and recommendations at the end
CycleWell Utility • Used to run the groundwater flow model numerous times and calculate stream baseflow depletion by model cell • Model is first run in the Baseline Condition • Model is then run in the Test Condition • In the test condition, one new well is added to the model • The stream baseflow difference between the two conditions is the effect of the test well on stream baseflow
CycleWell Utility (continued) • CycleWell records the results of the test simulation in an Access database • CycleWell then moves the test well to another location based on user-specified parameters and runs the model again • The Access database has a query that calculates stream baseflow depletion by taking the difference between the baseline condition and the test condition
CycleWell Utility (continued) • CycleWell is being used to calculate stream baseflow depletion for every model cell in the COHYST area • The current analysis looks at the cumulative volume of stream baseflow depletion at the end of 50 years beginning in 1998
CycleWell Utility (continued) • The Western Model Unit causes CycleWell problems because some test cells go dry during the simulation • These problem cells can be identified and deleted from the analysis, but the deleted cells cause an incomplete map of stream baseflow depletion • Use of injection well instead of pumped well fixes dry cells, but does it change the results?
Comparison of Different Injection or Pumping Rates – 1 Stress Period • The standard pumping/injection rate was 8,000 ft3/d (about 42 gal/min) • The alternate pumping/injection rates were 4,000 ft3/d and 16,000 ft3/d • Differences were calculated as stream baseflow depletion/accretion at the standard rate minus stream baseflow depletion/accretion at the alternate rate
Test Locations • CycleWell was run on five equally spaced columns and five equally spaced rows • 1,863 active cells were tested • Stream baseflow depletion/accretion was calculated for the North Platte basin and the South Platte basin • Many cells have nearly zero stream baseflow depletion, which affects the statistics
Conclusions: P-8,000 versus P-16,000 • Stream depletion could not be computed at about 20 percent of cells because they dried up • Differences in stream depletion were not related to absolute value of stream depletion • Differences in stream depletion were larger with small saturated thickness and were smaller with large saturated thickness
Conclusions (continued): • In North Platte basin, also had substantial differences with large saturated thickness in test cell, but small saturated thickness between test cell and stream • In North Platte basin, 98 percent of test cells were between -2.0 and +1.8 percentage points • In South Platte basin, 98 percent of test cells were between -0.0 and +0.3 percentage points • Statistics were affected by many cells having stream depletion near zero
Conclusions: P-8,000 versus P-4,000 • Stream depletion could not be computed at abut 16 percent of cells because they dried up (less than with P-16,000) • Differences were not related to absolute value of stream depletion and were related to saturated thickness • In North Platte basin, 98 percent of test cells were between -1.9 and +3.5 percentage points • In South Platte basin, 98 percent of test cells were between -0.3 and +0.1 percentage points
General Conclusions about Pumping • Pumping rate of 4,000 ft3/d was superior in that fewer test cells went dry • Except for dry cells, different pumping rates tested produced similar results • Range of 98 percent of the cells was larger for P-8,000 v. P-4,000 than for P-8,000 v. P-16,000 • Use of pumping test well results in large areas without computed stream baseflow depletion • Areas without computed stream depletion have small saturated thickness, and are unlikely to be developed for groundwater irrigation
Invalid Calculation Cells • Using an injection well eliminates the dry cell problem that occurred with a pumping well • No invalid calculation cells with injection rate of 16,000 ft3/d or with 4,000 ft3/d
Conclusions: I-8,000 versus I-16,000 • Use of injection test well eliminated dry cells and resulted in complete coverage of stream depletion • Differences in stream depletion were not related to absolute value of stream depletion • Differences in stream depletion were larger with small saturated thickness and were smaller with large saturated thickness
Conclusions (continued): • In North Platte basin, also had substantial differences with large saturated thickness in test cell, but small thickness between test cell and stream • In North Platte basin, 98 percent of test cells were between -5.2 and +0.8 percentage points • In South Platte basin, 98 percent of test cells were between -0.9 and +0.0 percentage points • Statistics were affected by many cells having stream depletion near zero
