4.5.1 Initial Fill During Adverse Water Year

pumped from Seminoe Reservoir for initial fill. See Sections 4.1 and 4.2 for a discussion of initial fill and make-up water sourcing, respectively.

The Project will operate by moving water between the constructed upper reservoir and the existing Seminoe Reservoir, with mean water years having no effect on pumped storage operations. High-water years could affect operations depending on how the Wyoming State Engineer chooses to permit the Project. Negotiations with the State Engineer are ongoing, but theoretically in a high-water year a spill-over event may occur at the Seminoe Dam.This spill-over event would theoretically result in a release of a portion of the Project’s water stored in Seminoe Reservoir under an excess capacity storage contract. Black Canyon is in the process of negotiating an agreement and the associated contractual arrangements with Reclamation, CAID, and the State Engineer that will allow the Project to recapture the release water downstream and trade it back for water in Seminoe Reservoir. Low-water volumes and surface elevations in Seminoe Reservoir have the potential to adversely affect initial fill, periodic make-up water, and Project operations, as discussed below.

As noted in Section 4.1, initial fill of the Project will require approximately 13,400 ac-ft of water, anticipated to be diverted and pumped from Seminoe Reservoir. A schedule for initial filling of the upper reservoir will be confirmed during the design process. Based on available information, Black Canyon anticipates access to sufficient volume in Seminoe Reservoir for initial fill under a contract agreement with CAID or a different water rights holder(s). If the scheduled initial fill coincides with a period of very low Seminoe Reservoir volumes, it is possible, depending on the seniority of the water rights secured by Black Canyon, that the Project’s access to water for initial fill could be curtailed by order of the Wyoming State Engineer. In addition, the initial fill of the Reservoir during a period of low Seminoe Reservoir volumes could implicate the North Platte River Decree and the mandatory water flows required to flow downstream to Nebraska. Under this low-water volume scenario, initial fill would be re-scheduled for a time not constrained by Wyoming State Engineer curtailment or the North Platte River Decree.

The schedule for initial fill could also be impacted by water levels in Seminoe Reservoir. The Project is designed to operate across the normal range of Seminoe Reservoir typical operation elevations of 6,290 feet to 6,357 feet (top of active storage). Since 1945, Seminoe Reservoir surface elevations have been below 6,290 feet approximately three percent of the time. When the water level in Seminoe Reservoir is below 6,290 feet, it is likely that Wyoming State Engineer curtailments would be in place, creating the adverse conditions discussed above. Additionally, the Project intake is designed to operate when Seminoe Reservoir is at surface elevation 6,290 feet and higher. If Black Canyon encounters a low Seminoe Reservoir elevation scenario at the time of scheduled initial fill, initial fill would be re-scheduled for a time not constrained by Seminoe Reservoir water levels.