Love Your Local Stilling Basin

We have written a great deal about the spillway at the Calaveras Dam Replacement Project. Completed in 2016, this spillway is the width of a six lane freeway, and the height of a three-story building. The spillway's job is to protect Calaveras Dam by allowing water from Calaveras Reservoir to flow safely around, and away from, the dam in extreme high water events.

We have neglected to highlight an important component of a spillway - the stilling basin. Today, we'd like to generate a little love for stilling basins.  

A stilling basin is a structure that dissipates the energy of the water rushing down the spillway. Without a stilling basin, water coming out of the spillway could scour out the foundation of the dam, the base of the spillway, and nearby creek beds. In short, the stilling basin is a sort of bodyguard for the dam.

Stilling basins come in a variety of types, but generally fall into two categories: a straight drop for lower elevations, or an inclined chute. The stilling basin at the new Calaveras Dam is an example of the latter category. To be specific, it is a United States Bureau of Reclamation (USBR) Type II stilling basin.  Our stilling basin is approximately 200 feet long, 45 feet high and 80 feet wide.    

Water flowing down the new spillway of the new Calaveras Dam will drop 200 feet in elevation before it reaches the stilling basin at the bottom.The stilling basin creates a hydraulic jump to slow down the high velocity water before it slowly, and safely, discharges into Calaveras Creek.

A view of the new stilling basin at the Calaveras Dam Replacement Project

So, let's hear it for the humble stilling basin!

See you around the Valley! 

Loma Prieta Earthquake Anniversary Week - The New Irvington Tunnel

Happy Friday

This week marks the anniversary of the 1989 Loma Prieta Earthquake. 

We've been blogging about the San Francisco Public Utilities Commission's efforts to seismically upgrade our water system for many years now. The $4.8 billion Water System Improvement Program is more than 96% complete as of this writing. The water system that supplies water to 2.7 million customers in four Bay Area counties is much more earthquake ready today than it was 5 years ago. 

In honor of the Loma Prieta Anniversary week, we wanted to remember a post from October of 2013 when a crucial seismic project for the Water System Improvement Program achieved a huge milestone. Final hole through. 

Miners worked long hours in the New Irvington Tunnel .

The New Irvington Tunnel Project ,which went into service in February 2015, is a new 3.5 mile long seismically designed tunnel. We mined the tunnel from different directions, and the moment the two teams met underground to complete the digging is called Final Hole Through.

See the October 2013 Story here.

One of the three road headers that excavated the New Irvington Tunnel.

Have a great weekend, everyone.

See you around the Valley!

Calaveras Dam Embankment Celebration- Photo Friday

The replacement Calaveras Dam has reached its full height of 220 feet.

The month of September marked a huge milestone for the Calaveras Dam Replacement Project.  The new replacement earth and rock fill dam has finally reached its full height and is nearly ready to begin impounding water this winter. 

You might have read about it or seen it on the news.  We had many media outlets out at the dam on September, 21, 2018 to cover the occasion.  

Here are some photo highlights in honor of Photo Friday.

San Francisco Public Utilities Commission Vice President Vince Courtney addressing the crowd.

Sharon Tapia, DSOD, Division Chief addressing the crowd.  DSOD or California's Division of Safety of Dams regulate dams in California.  They were a key partner in the construction of Calaveras Dam. 

General Manager Harlan L. Kelly, Jr., was joined by SFPUC Commissioners, SFPUC Deputy General Managers, and representatives from the Bay Area Water Supply and Conservation Agency to make it official with a ribbon cutting. 

Here is the entire Calaveras Dam Replacement Project Team atop the new dam.








The project isn't completed, however. The crew will work on completing the approach channel, constructing access and roadways throughout the site, restoration and revegetation, placing instruments, and installing gates and security systems. 

The overall project is 94% complete and is scheduled to be completed in spring 2019.

See you around the valley!