What's the Big Deal about an Approach Channel?

We are building a new earth and rock fill Calaveras Dam right next to the existing 93 year-old dam (directly downstream of the existing dam as they say in the dam industry.)  As many of our previous blog posts have been tracking, we have been busy building the new dam, foot by foot, from the bottom up like a layer cake. A very large layer cake.

Our Calaveras cake is high enough now to allow us to begin to excavate out the approach channel to the new dam this week.

"What is an approach channel?" you ask. An approach channel is a breaching of an existing dam in order for its adjacent reservoir to come in contact with it. We will remove a portion of the existing dam (500,000 cubic yards of it to be exact) to allow reservoir water to eventually fill in the space between the old dam and the new dam. The old dam will look like a peninsula in the reservoir when the project is done. 

"Why not remove the old dam in its entirety?" We don't have to. Complete removal would be expensive, environmentally difficult, and not necessary to operate the reservoir. 

The start of excavation of the approach channel means that we have reached a high enough elevation with the new dam to safely begin carving out a huge chunk of the existing dam. It's a coming of age for the new dam, if you will. A significant milestone. 

Here is what the approach channel looked like at the beginning of last week.



And, here is what it looks like this week.




The channel will be lined with large rocks called rip rap to protect it from erosion so the channel will be ready when we start to refill the reservoir this fall.

Approach channels may not seem exciting at first glance, but we at the SFPUC are thrilled!

See you around the valley!