Colorado's Plan for Future Depletions

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Colorado's Plan For Future Depletions January 12, 1998 Documentation as Required by Cooperative Agreement, Page 10 Milestones W6-1, W7-1, W8-1, and Tab 3B(I)E . Transbasin water is not part of the native flow of the South Platte River. There is no depletion to South Platte flows associated with its use. When transbasin water is used within a municipal water system, a portion of it is consumed due to the municipal use and the remainder of it returns as an accretion to the South Platte River system in the forms of wastewater and lawn irrigation return flow. While there may be subsequent use of this return flow, this phenomenon is addressed separately under water reuse calculations (for subsequent municipal use) or under transit loss calculations (for subsequent irrigation use). 5.2.2 Nontributarx Groundwater For each region, the accretions/depletions for each month from nontributary groundwater are calculated as follows: regional new municipal water use x % of nontributary groundwater in each region's water supply mix x nontributary groundwater use pattern for that month x monthly municipal return flow factor for that month. Non.tributary groundwater is not part of the native flow of the South Platte River. There is generally no depletion to South Platte flows associated with its use. When nontributary groundwater is used within a municipal water system, a portion of it is consumed due to the municipal use and the remainder of it returns as an accretion to the South Platte River system in tre forms of wastewater and lawn irrigation return flow. While there may be subsequent use of this return flow, this phenomenon is addressed separately under water reuse calculations (for subsequent municipal use) or under transit loss calculations (for subsequent irrigation use). 5.2.3 Aqricultural Conversion For each region, the accretions/depletions for each month from agricultural conversion are calculated as follows: regional new municipal water use x % of agricultural conversion in each region's water supply mix x agricultural conversion use pattern for that month x [municipal consumptive use (36%) - irrigation consumptive use (45%)] Municipal water use in Colorado is known to be less consumptive than irrigation use because most municipal use is for indoor purposes. When irrigation water is changed to municipal use, it is shifted from a higher to a lower level of consumptive use. Therefore a single municipal use of changed irrigation water would result in net accretions to the South Platte River due to the difference between irrigation consumptive use and municipal consumptive use.