2008-09-23_HYDROLOGY - M1984040 - Laserfiche WebLink

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Mary R. Halstead, P.E. September 23, 2008 Page 2 of 5 no. M84-040 allows for a maximum exposure of 8.5 acres of ground water at this site. Evaporative depletions to the South Platte River were calculated as the gross Chartier Pond evaporation less a portion of the historical consumptive of native vegetation prior to pond construction. Gross evaporation from the pond is estimated to be 50 inches per year, for a total evaporative loss of 25.83 acre-feet per year. A phreatophyte credit of 18.10 acre-feet from 6.2 acres of native cottonwoods has been applied to this SWSP (Table 1). Computation of evaporation under this SWSP was also reduced during the ice cover period. You have assumed the pond will be ice covered during the month of January. However, for the purpose of this SWSP, the Applicant shall replace the net evaporation depletions from the exposed ground water surface area that may occur during the assumed ice cover period (month of January) for any time that the pit is not completely covered by ice. Computation of the net evaporation during any time that the pit is not completely covered by ice shall be determined as the pro-rata amount of the monthly gross evaporation rate distribution amount identified in the State Engineer's General Guidelines for Substitute Supply Plans for Sand and Gravel Pits, subtracting the pro-rata amount of the effective precipitation for that period. The evaporation for the 6.2 acres during the months of November through March was calculated as the difference between gross evaporation and the effective precipitation, where the effective precipitation is equal to 70% of the total precipitation. Therefore, computation of evaporation under this SWSP was also reduced during the months of November through March period. The anticipated net depletion for this SWSP is 6.81 acre-feet of evaporation from up to 6.2 acres of ground water exposed after December 31, 1980. Although mining is not proposed to occur during the term of this SWSP, if mining does occur, Mr. Chartier estimates he could mine a 125- foot by 40-foot section of the pond in 2009 (0.1 acres surface area). Assuming an average mining depth of 15 feet and a depth to ground water of 4 feet, approximately 0.15 acre-feet of water would be lost with the mined product. In the event mining at the site does occur during the term of this SWSP, the exposed surface area will increase from 6.2 acres to 6.3 acres. Accordingly, the applicant shall amend the accounting form to include the additional evaporation depletions from the additional 0.1 acres of exposed ground water surface and the Applicant is required to obtain a well permit that allows for the exposure of 6.3 acres of ground water. No water is proposed to be used for dust control and the applicant has not proposed to wash the mined gravel, thus no additional water uses are included in this SWSP. The timing of depletions from the 6.2-acre pond was calculated using the Integrated Decision Support Alluvial Water Accounting System ("IDSAWAS") model with the 7-day SDF option starting in water year 1997 and going through the end of October 2009. Replacement Sources CDOW owns one share of the Jackson Lake Reservoir and Irrigation Company Stock which will be used to replace irrigation season depletions. This share was one of the two shares changed to augmentation in case no. W-8561-77. This share has not been used at the location described in case no. W-8561-77 since CDOW acquired the property and share in 1983. The decree in case no. W-8561-77 states that the "Jackson Lake Private Right yields an average of 16 acre-feet of water per year per right and the historical consumptive use of this water for irrigation purposes has been 50% of the delivered amount, so that the Applicant is entitled to the amount of consumptive use or 16 acre-feet for the two rights combined". Thus the consumptive use amount for CDOW ownership of one share is 8 acre-feet. The attached Table 3 presents irrigation season depletions of 3.4 acre-