Conservation News
San Clemente Dam Seismic Retrofit Project
By Dougald Scott
San Clemente Dam Seismic Retrofit Project
By Dougald Scott
San Clemente Dam sits at the confluence of the Carmel River and San Clemente Creek, about 20 river miles up Carmel Valley from the coast. Constructed in 1921, it is a concrete arch 106 feet high and 300 feet across. Over the years more than 2.5 million cubic yards of sediment have accumulated behind the dam, reducing its water storage capacity to about 10% of the original 1,425 acre-feet. In 1992, the Division of Safety of Dams determined that San Clemente Dam would not withstand a major earthquake or flooding event and ordered the dam owner, California-American Water Company (a privately held company), to bring the dam into compliance with current safety standards. Now, 14 years later, a draft EIR/EIS has been filed for the project (www.sjd.water.ca.gov/environmentalservices/sanclemente/index.cfm).
In addition to safety concerns, the dam has posed serious problems for migrating steelhead since it was built. The Carmel River steelhead run is the largest south of Monterey Bay. The dam is equipped with a fish ladder that requires fish to ascend 68 feet to the reservoir. It does not conform to the current fish ladder standards promulgated by NOAA Fisheries. The shallow water condition in the reservoir creates significant warming of the downstream river flows during the summer months, severely impacting the rearing habitat for juvenile steelhead.
The EIR/EIS presents four alternative plans to meet seismic and flooding safety standards:
* Proposed Project (by the dam owner): calls for retrofitting and thickening the existing dam and constructing a new fish ladder. It will require continued sluicing of sediment to keep the fish ladder operational. This will result in the transport of significant amounts of sediment downstream, which will directly affect redds and juvenile and adult steelhead in the river.
* Alternative 1: calls for notching the existing dam with the removal of approximately 1.5 million cubic yards of sediment from behind the dam, and replacing the existing fish ladder. The sediment would be transported by conveyer belt to a disposal area east of the dam. It will also require continued sluicing of sediment to keep the fish ladder operational, and will result in the transport of significant amounts of sediment downstream.
* Alternative 2: calls for removing the dam and approximately 2.5 million cubic yards of sediment from behind the dam. The sediment would be transported by conveyer belt to a disposal area east of the dam.
* Alternative 3: calls for rerouting the Carmel River for a short distance, and removing the dam. This alternative takes advantage of a narrow finger of land, which separates the Carmel River and San Clemente Creek arms of the reservoir, and runs to within two hundred feet of the dam. The sediment in the San Clemente Creek arm of the reservoir (380,000 cubic yards) would be moved to the Carmel River arm, where the bulk of accumulated sediment already resides. All of the sediment would be stabilized to prevent erosion. The Carmel River arm (where the sediment is deposited) would be permanently bypassed by cutting a 450-foot-long channel through the finger of land separating the two arms, approximately a half mile upstream of the dam.
* Alternative 4: No project
Clearly, dam removal provides the best long-term benefit to steelhead and the environment in general. It makes no sense to maintain a structure that has no real function while at the same time creating serious problems for migrating steelhead. Of the two dam removal options, Alternative 3 will result in fewer disruptions to fish and wildlife and local plant communities.
The major irreversible impact of Alternative 3 will be the construction of the diversion channel from the Carmel River into the San Clemente Creek streambed. Blasting will be required to remove the large volume of rock separating the two streambeds. The blasted rock will be reduced to 1-foot size and used in armoring the diversion dike face. Habitat complexity would be promoted within the new channel by constructing pools, runs, and riffles to provide suitable depth and velocity conditions for steelhead migration. Disruption to migrating steelhead during construction will be at least partially mitigated by a trap and truck operation around the construction site. Considering the two dam removal alternatives, channel diversion appears to be the best choice.
According to articles in the Monterey Herald and the Monterey County Weekly, Alternative 3 has won strong support among conservation groups, community groups and many local politicians. The Carmel River Steelhead Association and the Monterey Peninsula Flycasters are solidly behind Alternative 3 as well. The NCCFFF Board of Directors has officially supported Alternative 3. I presented this information at our June club meeting, and with a motion and vote was instructed to write letters to the responsible agencies stating SCFFÕs support of Alternative 3. The letters have been sent.
LOS PADRES DAM
If and when the San Clemente Dam issue is resolved, there will still be an 800 pound gorilla in the Carmel River closet. The Los Padres Dam is about 4 miles upstream from San Clemente Dam, with about 14 miles of steelhead habitat upstream of the reservoir. There is no fish ladder and upstream steelhead migrants depend upon a trap and truck operation. Downstream juveniles must pass over the spillway. The dam was built in 1949 and is presently more than one third filled with sediment. It soon will no longer serve as a functioning storage facility and face the same options as the San Clemente Dam.
General water overdraft in the whole Carmel Valley is also a constant threat to the watershed's steelhead. According to the EIS/EIR: "Summer rearing habitat for juveniles is believed to be the most critical limiting factor for juvenile steelhead production in the Carmel River BasinÉ Each dry season, depending on the amount of winter rainfall and pumping volume from the Carmel Valley, the river downstream of Robles del Rio can dry back from one mile upstream of the mouth up to 5 to 8 miles causing a loss of rearing habitat." Water district staff conducted 49 rescue operations in calendar year 2002, capturing 36,398 steelhead from drying in reaches of the lower Carmel River. The rescued fish were released into viable habitats upstream; 521 fish died during rescue and transport operations.
This river needs help! For more information on how you can help, visit the Carmel River Watershed Conservancy at www.carmelriverwatershed.org, or the Carmel River Steelhead Association at www.carmelriverwatershed.org/crsa.html.