Water Management Committee Workshop No. 1

The Water Management Committee (WMC) Workshop No. 1 with the consultant, Boyle Engineering, for the Water Conservation/Supply Study (Study) began at 10:15 a.m. at the U.S. Fish and Wildlife Office in Lakewood, Colorado. The Chairman noted the meeting topics of Workshops No. 1 and No. 2 had been switched and Workshop No.1 addresses Consumptive Use and Hydrologically Connected Ground Water and Workshop No. 2 addresses the Long List of Alternatives. Due to scheduling conflicts of some WMC participants that specifically wanted to attend the Workshop on the Long List of Alternatives, comments regarding the Long List of Alternatives will be taken by the Chairman until close of business September 1, 1998. In the future, any changes in meeting topics/schedules will be made only after notification of all WMC participants and approval of the WMC Chairman.

The Boyle Team reviewed with the WMC four methods used to calculate Consumptive Use (evapotranspiration) outlined in Boyle's memorandum distributed to the WMC by letter from the Chairman dated August 5, 1998. The advantages and disadvantages of the Christiansen Pan Evaporation, Blaney-Criddle Temperature, Jensen-Haise Radiation, 1963 Penman Combination, and Penman-Monteith Combination methods were discussed. Based on the Study's time period of 1975 through 1994 and the monthly time step that will be used, the recommendation from the Boyle Team was to use the Soil Conservation Service (SCS) modified Blaney-Criddle Temperature Method.

It was the decision of the WMC to use the SCS Blaney-Criddle method for estimating crop consumptive use for the Study. Standard coefficients for the SCS Blaney-Criddle method identified in Technical Release No. 21 (TR-21) will be used. The Crop Irrigation Requirement (CIR) will be calculated as the crop consumptive use minus the effective precipitation. The effective precipitation will be determined using the method presented in TR-21. Sensitivity analyses may be performed using localized coefficients to bracket the range of results.

The Boyle Team was asked by the WMC to prepare a memorandum on this decision about the consumptive use method selected, including an evaluation matrix (score sheet) of the methods similar to the one provided in their memorandum with brief verbiage of advantages/disadvantages, without assigning numerical ratings. This memorandum will be reviewed by the WMC and become part of the Study Report.

After a lunch break from 11:30 a.m. to 12:45 p.m., the workshop continued with the topic of Hydrologically Connected Ground Water. The Boyle Team reviewed with the WMC four proposed methods for analyzing the stream/ground water interaction outlined in Boyle's memorandum distributed to the WMC by letter from the Chairman dated August 5, 1998. The methods discussed included Fix Distance, Variable Distance, Stream Depletion Factor (SDF), and Numerical Modeling.

The Fix Distance Method assumes wells within a bandwidth of about seven (7) miles from a river cause depletions, and the physical distance a well is from the river is immaterial. The Variable Distance Method accounts for a well's proximity to the river. Both methods lack a quantitative basis.

The SDF Method was developed from an analytical solution of ground water flow using physical properties of distance to the river, transmissivity, and storage coefficient. Values for the SDF Method have previously been mapped for most of the Platte River Basin in a study conducted by the Missouri Basin States Association (MBSA) at a scale of 1 inch = 2 miles. Refinements to the mapping of SDF values at a scale of 1 inch = 1 mile have been done by the U.S. Geological Survey (USGS) for a sub-area of the MBSA Study on the South Platte River in Colorado. Areas not mapped include the upper reaches of the South Platte River and the reaches of the North Platte River above the Laramie River. As described in the MBSA Study, SDF values developed by the MBSA and USGS were calibrated by finite difference modeling at intervals along the river. Alternatives to be evaluated in these unmapped areas could be assigned SDF values calculated from the theoretical equation SDF = a²S/T. The SDF Method was developed for analyzing "point" stresses. Stresses over large areas would need to be idealized into evenly distributed "point" stresses. This method is not suitable for evaluating surface/ground water interaction in multi-layered aquifer systems, but analytical solutions for the exchange of water between aquifers could be adapted.

Numerical Modeling provides the ability to model complex ground water systems and obtain quantitative solutions. However, numerical models require extensive data input and development time. It was suggested to have the Boyle Team inventory the existing ground water models and use an existing model to evaluate any alternative identified within the model's boundaries. It was pointed out that the Scope of Work in Boyle's contract does not include the inventorying of ground water models, and the Boyle Team indicated that obtaining existing models and verifying them for use would be very time consuming. The WMC members requested a copy of the final Scope of Work be provided to them. The Chairman will obtain a copy and distribute it to the WMC.

After a break from 2:30 p.m. to 3:00 p.m., the Boyle Team reviewed with the WMC a scoring sheet they used to rate the methods and form their recommendation. The Boyle Team recommended using the SDF Method. The WMC accepted the recommendation and the Boyle Team was instructed to use the SDF Method. The Boyle Team was asked by the WMC to prepare a memorandum on this decision about the ground water modeling method selected, including an evaluation matrix (score sheet) of the methods similar to the one reviewed at the workshop with brief verbiage of advantages/disadvantages, without assigning numerical ratings.

Jon Altenhofen, Becky Mathisen, and Mike Drain were asked to review values of transmissivities in their respective States and compare with SDF information to verify the method. This group will report at the next WMC meeting.

The WMC discussed the time to full development (steady state) associated with the alternatives that are hydrologically connected. It was identified that some alternatives would require one or more years to reach a steady state condition and until the steady state condition was reached the alternative would not provide full benefit in terms of water contributions to the Program. The Boyle Team will evaluate all alternatives based on a steady state assumption over the 1975 through 1994 study period. The estimated time for an alternative to reach steady state will be documented. The concern is, how will the time for an alternative to reach steady state be considered with regard to the implementation of the Program? Will a potentially viable alternative be screened out because its estimated time to reach steady state and contribute water to the Program is too great? Further direction is needed from the Governance Committee (GC) regarding the implementation of the Program and the time to implement such alternatives.

Jon Altenhofen, Becky Mathisen, and Ann Bleed were assigned to examine the LandSat imagery and well location data for their respective States and report at the next WMC meeting. The WMC is preparing to provide well location data and the LandSat imagery to the Boyle Team for the Study. This information will be needed to investigate ground water and conjunctive use alternatives outside of the previously mapped SDF values.

The meeting adjourned at 5:00 p.m.