Friday, June 23, 2017

Building Dams in Earthquake Regions Part I

The First Two Calaveras Dams

As Californians, we live with the possibility of earthquakes.  Here at the Calaveras Dam Replacement Project, we are constructing a new earth and rock-fill dam that will be strengthened to resist the seismic forces and withstand a 7.25 magnitude earthquake. 

Dam technology has evolved since we completed the original dam in 1925. In a two-part series, we’re going to take a look at how our predecessors built the previous Calaveras Dam, which has served us well for 90 years, and what new technologies and construction methods we are using for the new dam to be ready for the next big quake.


The original Calaveras Dam (construction spanned 1913 to 1918) was constructed using the so-called hydraulic fill method.  Basically, to create the impermeable 'puddle core', fine soils were washed off the surrounding slopes with high pressure water cannons, and this slurry was collected between two 'training' dikes on both sides of the dam’s core.

During gold mining in the Sierra foothills, this method was used to build much smaller dams to impound water for hydraulic mining. But scaling this method up to this size had some serious problems. 

The first Calaveras Dam, nearly complete in 1918. It was the largest earthen dam in the world at the time.

The process did not allow excess water in the puddle core to dissipate, and this extra weight exceeded the ability of the upstream shell to retain it, and it failed as it neared completion.



The second (current) dam was completed in 1925 and was built on the remains of the first dam. For the current dam, soil was compacted in the core, primarily by running heavily-loaded wagons over it (pulled by mules). In this photo you can see the mule trains compacting the core.



The second Calaveras Dam, shown in 1926.

However, one problem that wasn't addressed during the construction of the current dam was the fact that alluvial soils (creek sediments including silt, sand, and gravel) were not removed before the first dam was constructed. Such saturated, loose sediments, which are removed during the construction of a modern dam, have the potential to 'liquefy' as they are shaken during an earthquake. 

It was for this reason that we at the SFPUC elected to build a completely new dam next to the existing dam.  And this time, things were different. 

Stay tuned to learn more!




Friday, June 16, 2017

Bald Eagle Photo Friday at San Antonio Reservoir

Happy Photo Friday!

This week’s pick comes courtesy of Kevin and Pat from our Natural Resources and Lands Management staff.

We have spent a lot of time writing about the nesting pairs of bald eagles who reside at Calaveras Reservoir and the pair near our restoration sites near San Antonio Reservoir in the SFPUC-owned Alameda Creek Watershed. But we’d like to introduce you to a more recent arrival to the San Antonio Reservoir area.   


This pair has made its home closer to our Turner Dam at San Antonio Reservoir.  Since it is the time of year when our pairs are on their nests taking care of chicks, our staff spotted two eaglets in their nest.

Once bald eagles find a nesting location they like, they tend to stay in the area. Which is why these bald eagles and our Natural Resources and Lands Management staff have gotten to know one another.  Our staff monitors the well being of these birds on a weekly basis. They all have been trained on bald eagle monitoring and behavior. Knowing these particular birds and bald eagle behavior enables our Natural Resources staff to know quickly if the birds seem ‘off’ because they have been disturbed by something.  



These little ones will fledge (develop the ability to fly) anywhere from 8 to 14 weeks of age. For now, they’re being fed a consistent diet of fish found in the reservoirs and creeks within the Alameda Watershed.

Healthy watersheds provide high quality water and also provide a safe haven for many amazing plants and animals. We consider it an honor and a privilege to look after these watershed lands, and all who live there, too.

Have a wonderful weekend, everyone!



Thursday, June 8, 2017

Sunol Valley Fire Safety #1


It’s always fire season in California, although it officially begins in May. Our warm and dry climate coupled with climate change has made California more susceptible to frequent wildfires.  According to CAL FIRE, between January 1, 2017 and May 20, 2017 there have been a total of 921 fires in California.

Here at Calaveras dam want to prevent wildfires by our watersheds. During the summer months we will be dedicating a series of fire prevention blogs with tips on how you can help prevent forest fires.


Today we will focus on equipment safety.  Operating equipment like lawn mowers, chainsaws and tractors improperly could ignite a wildfire.  However, according to CALFIRE there are simple steps that you can take to prevent these types of fires.

(Image courtesy of http://pacificsun.com/home-garden-lawn-be-gone/)

Equipment Safety Tips:
·       Mow during the cool time of day before 10 a.m. while there is still dew on the ground, not during the day and especially not when the wind is blowing.
·      Remove rocks and metal from the year that could be hit by the mower and cause sparks. 
·       Use a weed eater with a plastic line when cutting dry grass not a lawn mower (use lawn mower on green grass only).
·       Don’t top off fuel tanks.
·       Make sure spark arrestors are in proper working order and there is no carbon build up.
·       When transporting tractors, mowers, and recreational vehicles make sure that chains on the trailers are not hitting the pavement as you are driving.
·       Take special care when using tractors in dry grass that can easily ignite. 
·       Last but not least, always have a least one of the following items with you: fire extinguisher, water supple or a shovel.

Wildfires have an effect on watersheds, reservoirs, and the quality of our drinking water. 
By protecting our watersheds we are protecting our environment. Remember metal
blades hitting rocks can spark a fire!

For more information on wildfires go to: http://www.preventwildfireca.org/Equipment-Use/