2011-12-07_HYDROLOGY - M1981058 - Laserfiche WebLink

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Mr. Mark A. McLean, P.E. December 5, 2011 DeBeque Pit SWSP Page 3 Previously, the Lathams dedicated 2 shares of the Larkin Ditch to the augmentation plan decreed in Case No. 2005CW76, which were associated with 6 acres of dry-up and a historical consumptive use of 12.7 acre -feet per year. This SWSP includes historical consumptive use credits from an additional 4.1 shares resulting in a total of 6.1 shares. Dry-up of 19.1 acres is required for use of the 6.1 shares. Mining activities are reported to have resulted in dry-up of 20.1 acres as shown in the attached Figure 2. The consumptive use credit associated with the 6.1 shares of the Larkin Ditch was calculated for the period 1972 through 2000 using the Modified Blaney - Criddle Method with daily temperature and precipitation data from the nearby Palisade weather station and it was determined to be 38.7 acre -feet per year and is presented in the attached Table 2. Delivery of the replacement water will be made in the same manner as described in Case No. 2005CW76. Specifically, 10 percent of the prorata ditch diversion for 6.1 shares will be diverted in the Larkin Ditch to replace ditch losses. The remaining 90 percent of the prorata diversion for the subject shares will be returned and measured to the Colorado River at or near the ditch headgate. Note that a comprehensive stream depletion analysis considering return flow lags may be necessary for approval of a plan for augmentation. The Larkin Ditch (senior right) water right was decreed in Case No. CA1927 for 25 cfs for irrigation purposes, and the First Enlargement of the Larkin Ditch (junior right) was decreed in Case No. W -176 for 12.5 cfs for irrigation purposes. The Lathams' 20.5 shares equate to a flow of 5.74 cfs of senior rights and 2.87 cfs of junior rights. The junior water right in the Larkin Ditch (appropriation December 31, 1950) was historically called out by the Shoshone Power Plant water right. Historically the water rights within the Colorado River Basin that are junior to the Shoshone Power Plant water rights have been allowed to divert without curtailment because of releases of water from the Historic Users Pool ( "HUP ") in Green Mountain Reservoir. Once the junior water in the Larkin Ditch is changed for augmentation purposes they will no longer benefit from the Green Mountain Reservoir releases under the HUP. Therefore the junior water in the Larkin Ditch cannot be used as a replacement source in this SWSP, unless the water is in priority. For the purpose of this SWSP you are proposing to use only the consumptive use credits available from the change of senior water rights in the Larkin Ditch (priority no. 2). The dry year average annual historical stream depletion from the senior water right in the Larkin Ditch is estimated to be about 38.7 acre -feet. The amount dedicated to this SWSP equates to 1.708 cfs of the senior right. The pit must be continuously dewatered until such time as the pit can be filled by ground water infiltration during a free river period, or an amendment to the SWSP must be requested and approved to include additional replacement water to offset the volume of water required to fill the pit during the call period. Conditions of Approval This SWSP is hereby approved pursuant to § 37 -90- 137(11), C.R.S., subject to the following conditions: 1. This plan is approved with the effective date of May 17, 2010 and shall be valid through April 30, 2012 unless otherwise revoked or modified. If this plan will not be made absolute by a water court action by the plan's expiration date, a renewal request must be submitted to this office with the statutory fee of $257 no later than March 15, 2012. 2. Well permit no. 59594 -F, was issued for a maximum total exposed surface water area in the pit of 6 acres, 4.4 acre -feet of water lost in the mined aggregate and 2.5 acre -feet of water used for dust control. Since the existing permit no. 59594 -F does not cover the additional amount of water lost in the mined product identified in this SWSP, the Applicant is required to obtain a new well permit for this site. The Applicant is required to submit a well permit application for a new permit within 30 days of receipt of this approval. We recommend the Applicant apply