A US$4.4M STUDY IS UNDERWAY to explore options for the restoration of river flows and to improve migration of anadromous fish at the 50.3m high Matilija dam in Verntura County, California, US.

The concrete dam is scheduled for removal as it no longer provides flood control, as was intended by the designers, due to the large volume of sediment that has accumulated behind the dam.

However, the removal and safe disposal of the accumulated silt is the main concern affecting the Matlija dam removal. Scientists who have studied dam removals say sediments and nutrients migrated downstream after dam removal and harmed plant and animal life.

The 1973 breaching of Fort Edward Dam on New York’s Hudson river released tons of PCB-laden soil, turning part of the river into a Superfund cleanup site.

Concerns that that mercury from California’s gold-mining era could be lurking in sediments behind the Yuba river’s Englebright dam is one reason that California is considering ways to restore fish populations there without removing the dam On Matilija Creek, though, dam removal is considered the only way to restore the river, leaving only the question of how to remove it without causing further damage. Long before the dam was built, the US Army Corps of Engineers (USACE) predicted soil washing down from the surrounding mountains would fill up Matilija reservoir. As a part of the removal, USACE is considering incrementally lowering the dam so the 4.6Mm3 of trapped sediment can slowly wash downstream, although such an approach would take at least 20 years.

USACE is also considering quicker fixes, such as using a slurry pipeline, a conveyor belt or trucks to remove the soil.

Depending which is chosen as a result of the study, the project could cost US$40M to $180M for dam removal.

Officials in the City of Benton in Maine, US, meanwhile, are considering the pros and cons of building a fish lift at the 4.3MW Benton Falls hydro dam against the option of removing the hydro facility. CMS Generation of Dearborn, Michigan, which leases the Benton hydro facility, is to be asked by Benton to build a fish lift without considering dam removal.

The agreement that allowed the Edwards dam in Maine, on the Kennebec river to be breached requires the Benton Falls dam and other dams farther upstream from Benton on the Sebasticook river – a tributary of the Kennebec – to provide fish passage by May 2003.

As a part of this agreement, the Newport dam was removed during July and August 2002. The Newport dam was located on the east branch of the Sebasticook river.

The Burnham hydroelectric project, constructed in the 1920s near Pittsfield, also on the Sebasticook, is affected by the same agreement. Burnham dam is owned by Consolidated Hydroelectric of Andover, Massachusettes.