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Regain lost storage capacity at existing San Clemente and Los Padres Reservoirs. Facilities include means to remove, dewater, convey, and dispose accumulated sediment. Trucking and slurry pipelines were considered as conveyance means. Slurry pipelines require 850-1,200 af/yr of water to move material. Thus, this method is not recommended, as annual water use may outweigh storage capacity gain. Operations must be coordinated with fish life cycle and river hydrology. |
Maximum capacity to be regained is 1,278 af at San Clemente Reservoir and 854 af at Los Padres Reservoir. Firm yield from dredging is minimal, but water rights could be regained by dredging, equal to regained capacity. Sediment management plans at San Clemente Dam do not include dredging there. Thus, the Los Padres site value of 854 af is assumed for this evaluation. |
Capital costs for 854 af at Los Padres site are roughly estimated at $11-40 million, based on $8-29 per cubic yard ($13,000-47,000 per acre-foot). O&M costs not provided in cited reports. These estimates do not include removal of annual sediment inflow, bulking factors, or mitigation costs, which could be substantial. Costs do not reflect possible income from dredged material, if separated into salable components. |
Up to 3 years needed for environmental review and to obtain permits. 5-15 years for truck haul-off (854 af), depending on disposal site, quantity, and weather conditions. At 20-af/yr infill rate, regular sediment removal is needed to maintain storage capacity at Los Padres Reservoir. |
Major Benefits: Recovered reservoir capacity obtained without inundating habitat. Avoids sediment passage over San Clemente Dam. Major Adverse Effects: Smothering of fishery and aquatic wildlife habitat downstream of dredge site during dredging period; water chemistry effects. Substantial, chronic, long-term traffic impacts from reservoir to disposal site. |
Dredging is technically feasible, but serious questions about environmental and economic feasibility remain. Dredging at San Clemente site is not likely based on interagency discussions in summer 1998. Only the Los Padres site will be considered in this analysis. Advantages include recovery of storage capacity without inundating new areas. Disadvantages include extremely high cost per acre-foot, substantial traffic impacts, location of suitable disposal site, and potential harm to fishery habitat during dredging. |
* "Feasible" means project is a reasonably foreseeable means to provide lawful supply for Cal-Am water system. See text for further discussion.