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Jan 28, 2008 7:29 pm US/Pacific
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How Will Sacramento's Weirs Prevent Flooding?
SACRAMENTO (CBS13) ―
The Sacramento River was measured at 12 feet at noon on Monday, but engineers don't talk about opening the weir as a last resort until it reaches 27 feet. This brings up the question: What is a weir? How does it work?
If you're thinking that a weir is like a dam, you're right. It allows water to escape.
"A weir is essentially a concrete sill or dam that can be used for different purposes," says Arthur Hinjosa from the Department of Water Resources.
For irrigation you might put a weir across a river to dam it up, raising the level for watering crops.
"For flood control we use low spots in the levee that have been armored to alleviate the pressure on the river," says Arthur.
There are six weirs included in the Sacramento River Control Project. Most, like the Tissdale weir, are gravity driven. When the water gets high enough, it flows over the top, like it's designed.
The one weir that is controlled is the Sacramento weir, located in Yolo County. That weir protects the city of Sacramento.
"When it's operated it's doing that, but it's also putting stress along the levees protecting West Sacramento," says Arthur.
That's why it's sometimes controversial as to when to open the weir: Quick enough that people living along the river don't flood, but no so soon that levees around Sacramento endure the kind of stress that puts levees in jeopardy of breaching.
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