Title
Bartlett Dam Modification
Description
This report provides the Transportation, Infrastructure and Planning Subcommittee with an overview of a U.S. Bureau of Reclamation and Salt River Project proposal to modify the Bartlett Dam on the Verde River and the potential impacts to the City's water resources.
THIS ITEM IS FOR INFORMATION ONLY.
Report
Summary
Sedimentation in Horseshoe Reservoir on the Verde River is adversely impacting the storage capacity in the reservoir, reducing the amount of water available to Salt River Project (SRP) customers. The City is particularly impacted because it has additional, separate water storage rights in the reservoir based on a 1950 investment in gates installed on Horseshoe Dam (Gatewater supplies). A recent appraisal study by the U.S. Bureau of Reclamation (Bureau) determined that the appropriate response to the loss of storage capacity is a modification of the existing Bartlett Dam downstream of Horseshoe to create a larger reservoir in Bartlett Lake. The larger reservoir would restore the lost storage capacity of Horseshoe Reservoir for SRP customers and the City, in addition to adding storage capacity which would make additional water resources available for interested parties.
The proposals for a modified Bartlett Dam are a 62-foot expansion which would create a 422,000 acre-foot reservoir (increasing water storage by 145,000 acre-feet), or a 97-foot expansion which would create a 628,000 acre-foot reservoir (increasing water storage by 352,000 acre-feet). For reference, this additional storage capacity is enough to serve 180,000 to 345,000 homes every year. Numerous water users, including the City, have expressed interest in this additional water, which will alleviate reliance on Colorado River supplies and reduce the risk of increased groundwater pumping.
The next step is a feasibility study led by the Bureau and SRP to determine the size of a modified Bartlett Dam, the cost, the need for additional water resources in the area, local interest, and environmental impact. SRP has asked the City and other interested parties to share the costs of the feasibility study. Due to the City's existing rights in Horseshoe Reservoir, SRP proposes that the City contribute $100,000 to the costs of the feasibility study and participate as a member of the Steering Committee. Staff anticipates requesting Council approval of the cost share agreement this fall.
If the Bureau of Reclamation recommends and Congress approves construction of a modified Bartlett Dam after completing the feasibility study, a construction cost sharing agreement with the parties who are allocated a share of the resulting increased reservoir capacity will be required. The total cost of the infrastructure could be $1 billion. The timeline for the project includes a feasibility study (two to four years), followed by Congressional authorization for construction, and construction (five to 10 years). Based on those estimates, a modified Bartlett Dam could be completed between 2028 and 2035.
The benefits to the City of a modified Bartlett Dam include recovery of the City's existing Gatewater supplies (135,000 acre-feet), as well as the opportunity to receive an additional allocation of capacity in a new Bartlett Reservoir. Considering the anticipated shortfalls in Colorado River supplies and the desire to maintain sustainable groundwater pumping, the additional water resources would increase the City's water security at a cost that is less than other options.
Location
Council District: Out of City
Department
Responsible Department
This item is submitted by Deputy City Manager Karen Peters and the Water Services Department.