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nontributary water for the replacement water, this office may object to the use of <br />these sources in a proposed decreed plan for augmentation. The decision to accept <br />these sources as adequate to protect the senior water rights may be determined by <br />the Water Court in which the plan is filed. <br />14. Nontributary, transbasin, or other consumptive use sources may be used for <br />replacement purposes in a substitute water supply plan provided adequate <br />engineering and documentation are supplied. Use of nontributary water must also <br />comply with the Statewide Nontributary Ground Water Rules and may not be used <br />for more than 98 % of the fully consumptive use losses, e.g., evaporation, dust <br />control and water removed in the product. Lawn irrigation return flow credits will not <br />be acceptable unless established by the water court. Irrigation return flows from the <br />Colorado-Big Thompson Project water cannot be used for replacement purposes. All <br />replacement water must be made appurtenant to the gravel pit site for the duration of <br />the substitute water supply plan. <br />15. Many plans utilize the historical consumptive use associated with irrigation water <br />rights as part of their replacement sources. All or a portion of the land irrigated by the <br />surface water right is dried up to provide historical consumptive use replacement <br />credits. This source of consumptive use replacement water will only be available to <br />replace irrigation season depletions unless sufficient water is placed in an <br />acceptable storage vessel for release during the non-irrigation season, or as <br />provided by change of use decree. <br />16. Since only the water court has the authority to approve changes in water rights, <br />those substitute water supply plans approved by this office that involve a change of <br />use may not be able to claim the period of time while operating under the approved <br />substitute water supply plan for historical consumptive use credit. <br />17. Analysis of historical consumptive use shall be based upon the modified Blaney- <br />Criddle method or other acceptable methods or determination from previous court <br />decrees for the subject water right, if applicable. The historical use analysis shall be <br />based on firm yield (most cases equal to dry-year yield). The water court may <br />impose less stringent conditions on the plan for augmentation based on a different <br />study period. Any non-use of the water right during a study period shall be included <br />in averaging historical use. Any occurrence of subirrigation must be documented and <br />considered in the historical use analysis. Documentation of historical irrigation may <br />be based on aerial photographs, sworn affidavits, court decrees, well permit files and <br />water commissioner diversion records. Estimates of irrigation efficiencies, ditch <br />conveyance efficiency, and subirrigation shall be based on acceptable engineering <br />references and standards. <br />18. The land to be dried up shall be documented to the satisfaction of the local water <br />commissioner. A copy of the dry-up covenant shall be submitted to our office and <br />recorded with the county clerk and recorder. Maintenance of historical return flows <br />from the former irrigated lands will be required if necessary to prevent injury to other <br />water rights. The timing of return flows may be calculated using Glover techniques <br />[parallel drain theory, stream depletion factor (SDF)], or numeric modeling.