Monterey, California may be one of the most beautiful areas on the West Coast, but is just like any other community in our country when it comes to the need for water infrastructure investment. I wanted to share some information about a project that California American Water is currently involved in, which goes to show that infrastructure needs take many forms in sometimes unexpected ways.
Built in 1921, the San Clemente Dam on the Carmel River in Central California once served an important water supply function to the region. But now, since its construction, the reservoir of the San Clemente Dam has filled up with so much sediment that 90 percent of its volume is made up of debris and eroded soil, rather than water. When it was constructed 90-plus years ago, little was known about building for earthquake safety, so in addition to dealing with the sediment buildup, it is now necessary to comply with modern seismic safety standards.
The San Clemente Dam has the same issues that are affecting other parts of our aging infrastructure, but a structure like a dam is on a whole different scale than even our largest distribution pipes. Now, I know what you’re thinking…why not just remove the structure?
Well, that’s exactly what the company is planning to do, but it’s more complex than you might think. There are 18 miles of potentially floodable riverbed below the dam and 2.5 million cubic yards of sediment behind the dam. If the dam came down, and the flow of the water and movement of the sediment wasn’t carefully controlled, it would be pushed downstream and cause problems for communities on the riverbanks. In addition, removing the sediment poses a real challenge – how do you transport it out of an environmentally sensitive area without causing significant impacts?
The team ultimately decided to remove the dam, but keep the sediment in place and re-route the river around it. Working with resource protection agencies, as well as environmental protection groups ensured support of this project because the dam serves as a barrier to threatened Central Coast Steelhead Trout. By removing the dam, steelhead will have unimpaired access to over 25 miles of natural spawning and rearing habitat. Rerouting the river into a gentle slope will make it suitable for fish passage, too.
Throughout the course of the project, the old dam structure will be slowly removed and replaced by a large boulder-based wedge to hold the sediment in place so it will be able to naturally go downstream and help the areas of the river where it has eroded.
When the project is completed, the San Clemente Dam will be the largest dam removal in California, and provide a great opportunity to learn more about post-dam removal sediment transport, channel response, and river restoration processes from studying the outcomes of the project, which could help guide all future dam removal in the West.
In early December, I participated in a meeting for research planning on the impacts of the dam removal on the Carmel River. From reviewing what has been done for other dam removal projects, I think the San Clemente dam removal will be viewed as the premier way to handle such a project. All in all, it’s going to be a great project with positive impacts on the watershed.
If you are excited to watch the dam removal and the restoration of the Carmel River, visit the dedicated website and sign up for regular updates. You may want to view the time lapse photos of the last dam “draw down” while you are there.
This project demonstrates how public and private interests can work together, and benefit far beyond what either could achieve alone. And it also shows what we can achieve when we apply long-term planning and big-picture thinking related to our infrastructure needs. Water infrastructure maintenance is not just about fixing aging pipes. Sometimes it can be even bigger.