Friday, June 20, 2014

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.

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