COMMITTEE AGENDA MEMORANDUM
Capital Improvement Program Committee
SUBJECT:
title
Calero Dam Seismic Upgrade and Water Reliability Analysis.
End
RECOMMENDATION:
Recommendation
Receive information and provide direction to staff.
Body
SUMMARY:
Calero reservoir contributes to both annual water supply and operational reliability. On an annual basis, Calero is capable of providing up to 9,500 acre-feet (AF) of water supply. However, due to structural deficiencies found in the dam, the reservoir is under a seismic restriction limiting normal storage to 4,585 AF. The capital project currently at approximately 60% design, will address the structural deficiencies restoring the reservoir’s full storage capacity as well as expanding the reservoir outlet capacity.
Because the reservoir is local, Calero provides a local water supply source which is used to recharge the groundwater basin and can also supply raw water directly to the District’s surface water treatment plants. This helps in responding to imported water outages and is critical to the District’s disaster recovery plan.
Water Supply:
Calero reservoir has an associated water right of 3,500 AF per year from the Calero Creek watershed. In addition, Calero Reservoir is the terminus for the Almaden-Calero Canal water right which allows up to 6,000 AF to be transferred from Almaden Reservoir each year into Calero Reservoir. Combined, these two water rights can provide up to 9,500 AF each year towards meeting the County’s overall water supply needs.
Calero Reservoir also provides local storage for imported water supplies, typically Central Valley Project (CVP) supplies brought in from San Luis Reservoir. From a turnout on the Cross Valley Pipeline, CVP supplies (as well as water from Anderson Reservoir) can be released directly into Calero Reservoir for storage and later use. This adds flexibility to the District’s raw water system providing an in-county storage option which allows the District to take delivery of imported water supplies which could otherwise be lost. Local or imported water stored in Calero Reservoir can then be put to beneficial use by releasing into Calero Creek for groundwater recharge or into the Almaden Valley Pipeline for delivery to the surface water treatment plants.
Operational Reliability:
Of the District’s ten local surface water reservoirs, only three can supply raw water to the District’s surface water treatment plants; Anderson, Coyote (via Anderson), and Calero Reservoir. These sources are critical during a CVP outage. When the District is not able to deliver CVP supplies from San Luis Reservoir due to a low point event, Pacheco Pumping Plant outage or other condition, the District utilizes these local storage supplies to supply the treatment plants with raw water until CVP deliveries can be restored.
Infrastructure Reliability Study:
Calero Reservoir is particularly critical in the District’s recovery plan for a major earthquake. In a significant seismic event, it is assumed that the South Bay Aqueduct will sustain significant damage (since the pipeline passes through areas prone to landslides) and will require significant time (greater than 60 days) for the State to make repairs and restore deliveries. It is therefore the District’s strategy to prioritize restoring supplies from the south.
Calero reservoir is the closest source of water to the water treatment plants, delivered through the Almaden Valley Pipeline. The top priority would be to repair the Almaden Valley Pipeline which at the time of the Infrastructure Reliability Study, was estimated to take less than 30 days to repair following a significant seismic event. Recently condition assessments of the Almaden Valley Pipeline indicate a worse than expected existing condition and will require additional rehabilitation efforts to restore the pipeline to service after a seismic event. Once the Almaden Valley Pipeline is repaired, Calero Reservoir can provide source water to the treatment plants. This would restore treated water production and delivery of minimum winter demands to retailers within 30 days, which is an acceptable service level for the retailers following a seismic event. As the closest supply source, deliveries from Calero Reservoir are the first priority. Repairs would then progress south restoring deliveries from Anderson Reservoir and finally, San Luis Reservoir. Without Calero, service outages could extend an additional 10-15 days, depending on the scenario. Additional system improvements would likely be needed to reduce service outages back to the accepted 30 day target. (Note that outage durations are estimates based on a variety of assumptions on earthquake location, resulting facility damage, and availability of repair equipment and crews; and could be shorter or longer in an actual seismic event.)
Other Reservoir Benefits:
In addition to annual water supply and operational reliability benefits, Calero Reservoir provides other benefits to the Community. As a watershed reservoir, Calero provides incidental flood protection to downstream residents. Although it is not a large watershed, during high rainfall events, natural peak flows are attenuated in the reservoir before spilling from the reservoir.
Calero is also one of only three in-county reservoirs which allows power boating and other recreational uses. It is heavily used by the public, and during the past season while Anderson Reservoir was not open to boating, Calero was one of the only boating locations available to the local community. This will be particularly true during construction of the Anderson Dam Seismic Retrofit Project, when both Anderson and Coyote Reservoirs will be unavailable.
Alternative to Retrofit:
Another seismic dam repair project located in the same watershed is the Guadalupe Dam Project. As part of the Guadalupe Dam Planning Study, the project consultant prepared an analysis of various project alternatives. This included partial dam removal and full dam removal options. It is assumed that abandoning the dam as-is would not be an acceptable alternative to the Department of Safety of Dams or the resource agencies. Therefore, some level of work would be required. The Guadalupe Planning Study estimated that the cost of partial dam removal would be about the same as the dam retrofit option. The cost of full dam removal is estimated at 1.6 times the cost of a dam retrofit. The high costs of partial or full dam removal are due to the large amount of material that would need to be moved as well as issues related to the mercury found in the reservoir sediments. It can also be assumed that significant mitigation and restoration efforts would be required by the resource agencies.
The analysis provided for the Guadalupe Dam project can provide a general idea of costs that might be expected at the Calero Dam site as Calero would have similar issues such as mercury. In addition to the capital costs of a dam removal alternative, the cost or impact of the lost benefits described above should also be considered.
ATTACHMENTS:
None
UNCLASSIFIED MANAGER:
Manager
Kurt Arends, 408-630-2284