Tuesday, January 26, 2010

Releasing the Rivers

According to an ENR article, State government officials and the California American Water Co. agreed on Jan. 11 to remove the 106-ft-tall San Clemente Dam on the Carmel River in Monterey County. The concrete arch dam, built in 1921, once provided drinking water to Monterey Peninsula residents, but its reservoir has since silted up 90%. In 1991, state dam inspectors also concluded the dam risked failure in a significant earthquake or flood event, which could release an estimated 2.5 million cu yds of sediment and more than 40 million gallons of water.

After a long, tortuous political process, a solution was finally developed between several parties, mostly to mitigate liability issues for the potential for sediment release. This sediment has resulted as the river silted up the dam over the last 90 years, which is about the expected useful life of a dam. Dams are not permanent water control features because of this natural process, and thus are not being planned as future structures in water retention and storage. Alternate strategies are being developed to use watershed management and techniques of returning water to the aquifers because of these inherent problems in retaining surface water. This also reduces the evapotranspiration that happens when large areas of retained water are held back in surface storage. Along with this comes habitat restoration and the return of fish population to the rivers.

One constituency for this dam removal has been the Carmel River Steelhead Association, which is tracking the dam removal process and participating in the Carmel River Watershed management. They have a nice flythrough of the river and its watershed on their website. The dam removals are part of a State Department of Water Resources effort to ensure the safety of residents living downstream of dams, which has a clearinghouse of Dam Removal information (CDRI). The CDRI is also asking for public submission of projects involving dam removal and river/watershed restoration to their comprehensive resource database.