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! 

Calaveras Dam Celebrates another Safety Milestone

According to the U.S. Department of Labor Occupational Safety and Health Administration (OSHA), nearly 6.5 million people work at construction sites across the nation on any given day. The rate of injuries for construction workers is higher than those workers in other job categories in the United States. On average, we could have 150 workers on site at the Calaveras Dam Replacement Project.

The construction crews at the Calaveras Dam Replacement Project work multiple shifts – both day and night – working with huge machinery on a very complicated job site in challenging conditions. And yet the construction crews, who work for the joint venture of Dragados USA, Flatiron Construction and Sukut Construction, celebrated a huge safety milestone this week. Our crews have worked 75,000 safe working hours for the last quarter (from September 24, 2015 through December 31, 2015) without any recordable safety incidents. In fact, to date, they have a total of 304,146 work hours without recordable safety incidents as of December 2015. The last lost time incident was recorded in 2012. The teams celebrated with a well-deserved barbeque lunch on site to celebrate their success, and remind each other of the need to continue with their best practices to keep everyone safe.

As we continue the critical work to complete the project, we applaud our teams for continuing to make safety a priority here at Calaveras Dam.



Construction team who perform major structural work at the dam
(Pictured in no particular order: Jose Rodriguez, Dewayne Grayer, Ben Simbra, Benny Jasper, Alfredo Simao, Miles Cheek, Tomas Orantes, Eddie Fuentes, Garrett Colvin, Mike Morrison



Construction work on the new spillway chute

A New Bridge for the New Year

We at the Calaveras Dam Replacement Project have been talking a lot about the new spillway under construction at the dam. And why not? It is as wide as a six lane freeway, with walls that are 40 feet tall, and it is 1500 feet long. We placed over 50,000 cubic yards of concrete into the structure to date, and it has been the major focus of activity at the dam for over a year.  Spillways allow dams to safely discharge water without overtopping. This is a key safety feature of any dam, particularly Calaveras Dam as it is an earth and rock fill dam.

Last week we sent out a traffic notice for users of Calaveras Road to be aware that three large trucks would be making a very special delivery for our favorite spillway – its bridge. So special that it had to be trucked in six sections all the way from Ohio.

The spillway bridge will allow future personnel to drive across the top of the spillway safely and access the top of the new dam and outlet works at the toe of the dam. Crews used special cranes to begin installation of the bridge this week. We will be completely done with the spillway this spring.

 

Photos courtesy of Lead QA Inspector Glen Gorski and QC Engineer Shary Truong

A Snapshot of our Spillway Chute and Stilling Basin Today

Spillways are important safety features on any dam. They allow for the safe discharge of high water in a reservoir around a dam.  And the new spillway at the Calaveras Dam Replacement Project is no different.

Work began on our spillway in March 2014. A total of 40,000 cubic yards of concrete, equivalent to one football field filled six feet deep, will be used to build the structure. All of the concrete is being supplied by our on-site concrete batch plant. The concrete is placed into the spillway in sections, or slabs. This spillway requires a total of 170 slabs, and we only have 18 more to go.

The spillway chute is 60 feet wide, equivalent to a five lanes of a highway. The slabs are strengthened with reinforcing steel bars and the entire structure is anchored to the bedrock to resist movement during an earthquake. 

The quality of the concrete used in the structure is key. It has to be kept at a cool temperature while it cures in order to prevent cracking. Sunol Valley in summer is anything but cool. That means our crews often begin cement pours at 2 o'clock in the early morning, the coolest time of the day.

The spillway is expected to be completed later this year. This will be a major milestone for the project to complete this important feature of the dam.

Nighttime Crews Working Away on the New Spillway for Calaveras Dam

What are construction crews doing at 2 a.m. at the Calaveras Dam? They are working in the pre-dawn hours to mix and place concrete for the new spillway. Over 40,000 cubic yards of concrete will be placed into the new 1550 ft concrete spillway for the Calaveras Dam Replacement Project. Crews have to work in the early hours to ensure the concrete maintains a precise temperature to cure and reach its optimum strength. We are approximately 30% complete with the concrete spillway work.

Read more about the spillway here. The projected completion for the Calaveras Dam Replacement Project is late 2018.

 Crews work on placing concrete for the slabs of the new spillway

Crews work early hours placing concrete on the new spillway. All concrete is mixed on-site at our batch plant reducing truck deliveries on public roads.

We are halfway there!

The Calaveras Dam Replacement Project team reached an important milestone for the project this week. Crews have excavated more than 5.4 million cubic yards of earth and rock material at the project site. This material would fill approximately 1,656 Olympic-sized swimming pools. A total of 10 million cubic yards of material is required to be moved for the entire project--- 6.5 million cubic yards to be excavated and 3.5 million cubic yards which will go into the construction of the new dam.  In addition, 10,000 cubic yards of concrete to date has been poured and placed in the new intake tower and the new spillway structure. Much work still lies ahead, but definitely something to celebrate for our hard working crews from Dragados USA /Flatiron/Sukut Construction Joint Venture.

Crews gather to celebrate reaching over 5 million cubic yards of earthen materials excavated

Concete work at the new spillway underway

An Ode to the Calaveras Spillways, old and new

Workers repair original Calaveras Dam spillway in 1939

What is a spillway?

A spillway is an important safety feature on a dam that impounds water behind it to prevent the dam from overtopping and suffering damage during a flood. The spillway is often an open chute or channel that allows water when it reaches a high level in the reservoir to safely bypass the dam and flow downstream without causing any damage to the dam.

History of the Calaveras Dam Spillway
The original spillway on Calaveras Dam was completed in 1925. In 1939, workers had to repair the original spillway after damage was caused by a flood occurred in the Winter of 1937-1938.

Spillway Work Today
Back in March work began on the new spillway. We have made much progress since then to construct the spillway, which will be 1550 feet long. Approximately 40,000 cubic yards of concrete, equivalent to one football field filled six feet deep, is being used to build the structure. All of the concrete is being supplied by our on-site concrete batch plant.
Because of its crucial function in dam safety, it’s important to make sure that the spillway structure stays intact during an earthquake on the nearby Calaveras Fault. So we are drilling anchors, a solid steel rod, about 25 feet into the rock around the spillway to provide support and prevent damage to the structure during any seismic activity.  We are installing 1,825 anchors, that’s a lot of anchors!  The spillway is expected to be completed in mid-2015.

View of the left wall of the new Calaveras Dam spillway. The purple anchor in the foreground will be encased in the concrete slab (foundation) being formed here. The exposed ends of the wall anchors will be encased in a block of concrete as part of the spillway wall.

Aerial view of new spillway taking shape at the left abutment.
Red arrows indicate the top of the spillway.

Calaveras Dam building a new and improved Spillway

Things sure look much different than it did in the early 1900s when the workers at the Calaveras Dam site were building the original spillway for the existing Calaveras Dam.  Today, we are building a new spillway over twice the size of the original.

Calaveras Dam workers rebuilding the spillway in 1933

Calaveras Dam workers today working on the foundation of
the upper portion of the new spillway

What’s the Spillway for?

A spillway is a structure used to control the release of flows from a dam into a downstream area. Spillways release overflow of water or floods so that the water does not overtop and damage the dam. When complete, the new spillway for the replacement dam will be approximately 1,550 feet in length and will be constructed using 40,000 cubic yards of concrete. Much work still lies ahead, but we are well on our way to rebuilding a critical feature of the replacement Calaveras Dam.