Final Environmental Assessment for the Tamarack Managed Groundwater Recharge Project

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270 days. For the 1943 -1994 study period, the average annual diversion by the wells for recharge in the Tamarack Plan would have been 22,950 acre -feet. Recharge from canal systems is accomplished during periods when there is unused canal capacity. These periods occur in the fall after the irrigation season until freeze-up, typically through the month of November, and during spring runoff when there are excess river flows. The average annual diversion for the 1943 -1994 study period by canals for recharge in the Tamarack Plan Project would have been 6,690 acre -feet for a total of 29,640 acre -feet by both wells and canals. Tables 1 and 2 list the reregulation results of the Tamarack Plan operations for this historical analysis of the 1943 -1994 period. Table 1 lists the monthly additions or increases that would have occurred to the hisforic Julesburg gage flows as a result of the accretions or return flows to the river caused by the groundwater recharge of the Tamarack Plan. These are net values and occurred for months when river accretions exceeded the diversions to the recharge basins. Table 2 lists the monthly net depletions which would have occurred for months when the diversions to the recharge basins exceeded the accretions in that month. From Table 1, the average annual net addition or accretion is 16.1 thousand acre -feet ( "kaf") while the average annual net addition for the April through September period is 10.0 kaf. From Table 2, the average annual net depletion is 20.0 kaf. The difference between the average annual accretion of 16.1 kaf and the average . annual depletion of 20.0 kaf is due to evaporation and some of the accretions to the river not being accounted for because they would have occurred after 1994, which is the last year of the modeled period. III. CRITERIA FOR OPERATION OF THE TAMARACK PLAN 19 - A. The components of the Tamarack Plan include participating existing and future wells or other water facilities which are operated to increase flows at the Julesburg gage during the period of April through September by an average of approximately 10,000 acre -feet over the flows that would otherwise occur during that period. All such facilities will be operated by Colorado and its water users in compliance with the requirements of the South Platte River Compact. B. Colorado will also operate the Tamarack Plan, after consultation with the manager of the Environmental Account in Kingsley Reservoir, in a manner that does not cause an increase in target flow shortages at the critical habitat unless requested otherwise by the Environmental Account Manager, as measured at the Grand Island gage and using FWS target flows which are then in effect, so long as (a) any target flow shortage is not related to the operation of the Environmental Account in Kingsley Reservoir outside of the scope of the Annual Operations Plan for the Environmental Account adopted by the signatories, (b) the use of wells within Nebraska which are in existence at the date of the Cooperative Agreement is not expanded or enlarged, or 4