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Dam being removed from river
• 1933 structure impedes fish, people
Dennett Dam
Work started last week to begin dismantling remnants of the old Dennett Dam, seen here to the west of the Ninth Street Bridge between Modesto and Ceres. Access to the site is being created on the south side (right side of this photo). - photo by Jeff Benziger

The small dam that has been in the Tuolumne River for over 85 years intended to create a lake near the Ninth Street Bridge but is an impediment for water craft and fish alike, is being removed.

Work began last week to start dismantling the submerged obstacle at a cost of $1 million. The lowest bidder came in much lower than the $2.4 million bid obtained in summer of 2017, said Nathan Houx, the city of Modesto’s Parks Planning and Development manager and the administrator of the Tuolumne River Regional Park JPA.

Removing the dam, Houx said, is “very important to encourage any boating activities” and could help with Ceres’ plans to have a boat launch at Ceres River Bluff Regional Park. It would also remove an impediment to the migration of Fall-run Chinook salmon and Central Valley steelhead. Right now salmon have a hard time going upstream to spawn, he noted. With the dam out of the way the fish can basically go all the way up to La Grange Dam without any barriers.

The city of Modesto and Tuolumne River Trust has been working to remove the 1933 structure for eight years, money being the chief obstacle. The expensive project is being funded by state grants and one private grant. 

The contractor on the project, Innovative Construction Solutions, will create a channel in the river bed and divert the river flow around the dam site. Once dismantled and pieces hauled out on the south side, the firm will level out the hole below the dam created by water erosion. The work could be finished by October.

Taking out the dam has been an obsession with the Trust. They say the dam makes it hard on boaters, kayakers and canoers, and the swirling undertow it causes may have contributed to three drowning deaths in the past 12 years. But it’s fish that gives them the greatest concern.

Adding to the cost is a litany of environmental regulations dictating how much material can be removed in a day, a survey for pond turtles, construction of a snow fence along the work site to prevent encroachment into adjacent riparian areas, the protection of valley oaks, as well as the replanting of trees and bushes destroyed in the process of moving big equipment in and out.

The decision was made back in the 1930s to build the dam to create a 97-acre recreational lake called Lake Modesto. After heavy flows in 1940 compromised the dam and lake, it was condemned by the state in 1947. Portions of the concrete foundation remain in the river may be seen in low-flow months like now.