Substitute Water Supply Plan Forum September 1 2004

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l 4 documentation are supplied. Use of nontributary water must also comply with the Statewide Nontributary Ground Water Rules or Denver Basin Rules as applicable. Water from wells decreed in Larimer County District Court Civil Action 11217 shall not be used as a source of replacement supply or substituted water supply in a substitute water supply plan. Lawn irrigation return flow credits may not be acceptable unless established by the water court. Irrigation return flows from the Colorado -Big Thompson Project water cannot be used for replacement purposes. Replacement water must be adequate in amount in duration to cover all post - pumping depletions. 13. Many plans utilize the historical consumptive use associated with irrigation water rights as part of their replacement sources. All or a portion of the land irrigated by the surface water right shall be dried up to provide historical consumptive use replacement credits. The land to be dried up shall be monumented to the satisfaction of the local water commissioner. Maintenance of historical return flows from the former irrigated lands will be required if necessary to prevent injury to other water rights. The timing of return flows may be calculated using Glover techniques [parallel drain theory, stream depletion factor (SDF)], or numeric modeling. Consumptive use replacement water from irrigation water rights will only be available to replace irrigation season depletions unless sufficient water is placed in an acceptable storage vessel for release during the non - irrigation season, or as provided by change of use decree. 14. Analysis of historical consumptive use shall be based upon the modified Blaney - Criddle method or other methods generally accepted in the engineering community for -calculating crop evapotranspiration or determination from previous court decrees for the subject water right, if applicable. The historical consumptive use analysis shall be based on a representative study period and the projected yield for the plan year must be adequate to meet augmentation requirements. Any non -use of the water right during a study period shall be included in averaging historical use. All sources of water for irrigation must be considered when determining historical consumptive use. Any occurrence ,of subirrigation must be documented and considered in the historical use- analysis. Documentation of historical irrigation may be based on aerial photographs, sworn affidavits, court decrees, well permit files and water commissioner diversion records. Estimates of irrigation efficiencies, ditch conveyance efficiency, and subirrigation shall be based on acceptable engineering references and standards. 15. Substitute water supply plans may use reservoir water released to the stream at the proper time and in the proper amount. Reservoir storage and releases are generally required to offset winter depletions. An analysis of the consumptive use of the reservoir water (if reservoir water is not decreed for augmentation purposes) shall be required. Dry-up of irrigated lands will be required if the only source of water available was the reservoir water used for irrigation. 16. An excavation that intercepts groundwater is considered a well; thus, the excavation may not be used for water storage unless it meets the standards outlined in the State Engineer's Guidelines for Lining Criteria for Gravel Pits.