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/




Friday, May 26, 2017

Blankets and Curtains for Calaveras Dam?


Here at the Calaveras Dam Replacement Project we are building what is called an earth and rock-fill dam. The replacement Calaveras Dam, like all so-called embankment dams, is made of mostly compacted earth (see a cross section of the future dam below). An important aspect of this type of dam is the management of water. All earthen dams leak, the important thing is to control where the water flows to protect the integrity of your dam.  In the case of the Calaveras Dam Replacement project, we accomplish this with blankets and curtains. 



No fooling! Here’s how it works.  For years, the crews onsite have been constructing an entire dam that extends more than 100 feet below the base of the future dam.  We call this a grout curtain. Grout for those of you not in the construction industry is a special mix of cement that can be injected or literally blown onto a surface to seal it.  


Grout Curtains

As you can see in the photo from 2015, crews drilled countless small diameter holes into the bedrock a hundred feet down below the future dam and injected the holes with pressurized grout. The grout effectively seals up cracks and fractures within the rock underneath the new dam.  We did this for years. Why is this grout curtain so important? It prevents water from seeping underneath the new dam and undermining it.  In essence we drilled an entire new dam underneath the future dam. 


Drainage Blanket

If you thought grout curtains alone were enough to protect the future Calaveras Dam, guess again! We need blankets, too. More specifically a drainage blanket. The drainage blanket prevents water from exiting to, and damaging, the down-stream face of the dam (the face of the dam away from the reservoir).  At the end of the drainage blanket we are constructing a ‘mini dam’ made out of the same clay material as the core to capture any water in the drainage blanket. You can see the drainage blanket being constructed here.  This ‘mini dam’ is also known as the seepage barrier.  This seepage water is then collected in an inspection well to monitor the condition of the dam.

The Calaveras Dam Replacement Project, along with its blankets and curtains, is more than 80% complete.

See you around the Valley!




Friday, May 19, 2017

Photo Friday at the Calaveras Dam Replacement Project


Did you ever look at a photo of yourself or a family member from a long time ago and compare it to a recent picture? For today’s Photo Friday, we decided to do just that for the Calaveras Dam and its replacement.




Calaveras Dam in 2011. The project groundbreaking was in 2011. 





Calaveras Dam in April 2017. The project is more than 80% complete. We have moved more than 8 million cubic yards of rock and soil to date. We have fully excavated and grouted the left and right abutments. And in the center of the picture, the core of the new Calaveras Dam begins to take shape.  The huge concrete spillway (as wide as a freeway) is visible at the lower right. Wow.

Construction on this project started in 2011 and is expected to be complete in April 2019.

To learn more about this project and see a time lapse video of all of this excavation, visit us here.  

See you around the Valley!



Friday, May 12, 2017

Photo Friday for the Birds

While this author spent time in the Sunol Valley this week, she spied an amazing bird. 

Sitting atop the construction fencing that keeps small (crawling) critters out of the construction site, was a bird with flaming yellow plumage accented with black.

This striking fellow (and yes it is a male, the females are much more subdued in color) is a Bullock's orioleThe Alameda Watershed is home from spring through summer to Bullock’s orioles, like this first-year male. They'll winter in Mexico or Central America before migrating north again next spring.

They dine on insects, fruit, and raid the occasional humming bird feeder for the nectar. 




See you around the Valley!

Thursday, May 4, 2017

Honoring Construction Safety Week in the Sunol Valley


With so much heavy construction work underway in the Sunol Valley, it is easy to forget that the men and women in the construction industry perform dangerous work often in difficult conditions to upgrade the Hetch Hetchy Regional Water System.

It is a good thing that the construction teams working on the two projects in full swing in the Sunol Valley keep safety in mind every single day.  However, this week was a little different. The teams at the Calaveras Dam Replacement Project and the Fish Passage Facilities within the Alameda Creek Watershed underwent additional trainings and reminders this week.

Why?

The first week of May is National Construction Safety Week.  Global construction industry leaders, including our contractors, joined together to form industry safety forums and an initiative called ‘Safety Week.’ The mission of Safety week is to raise awareness within the construction industry ensuring “We are Stronger and Safer Together.”

How strong?

Here in the Sunol Valley, the number of recordable workplace incidents is well below the industry average. At our Fish Passage Project, workers have clocked in over 70,000 work hours since April 2016 with zero recordable incidents.  At the Calaveras Dam Project, the largest project in the Water System Improvement Program has worked over 220,000 work hours since July 2016 with zero recordable incidents. 

Working in heat and rain, on large earth-moving equipment or in tight spaces next to a creek, our crews are showing that every week is safety week.

We are proud of our teams out in Sunol Valley! Stay safe out there.

Crews overseeing operations at the future Fish Passage Facilities

Center of photo shows construction crews at Calaveras Dam placing
Clay Core materials in the replacement dam at elevation 567 ft