Wednesday, February 15, 2017

Oroville Dam: Nation's Tallest at 770 feet

(Satellite)

This dam is one of the storage dams to catch Spring runoff water in northern California to supply central and southern California with water throughout the year. In 2017 they had significant runoff and the main spillway started breaking. They closed it and then discovered the emergency spillway was breaking. So they switched back and significantly broke the main spillway. (2019 Update: it cost over a billion dollars to fix the damage because the California Department of Water Resource would not spend $4.5m to repair some problems found during an inspection of the main spillway.)
Video from California Department of Water Resource
This scene at 0:06 shows water flowing over the emergency spillway and parking lot.

Construction of the tallest, 770 foot, dam in the country:
(new window)



This historic video is an overview of the 450 mile aqueduct and Oroville Dam project.



The main spillway was designed to handle 125,000 cubic feet per second (or 125 kcfps). During previous "rain events," it did handle that amount. If a hole had not broke open in the main spillway, I would have never heard about this dam because the main spillway would have handled this rain event. But because of that hole, the officials got scared and decided to limit the flow to 55 kcfps and allow the lake to fill up at 6-feet per hour and go over the emergency spillway. 12 kcfps normally goes through the powerhouse, but they had to shut that down because the broken concrete that flowed into the Thermalito Diversion Pool was backing up the water higher than the powerhouse could handle. The design capacity of the emergency spillway was 300 kcfps. But after they saw the damage being caused by just 1% of its design rate, they decided to open the main spillway to 100 kcfps. After a few hours that caused the water to quit going over the emergency spillway. The broken spillway quickly eroded down to competent bedrock and was used for the remainder of the Spring.

They are letting the main spillway run at 100 kcfps to lower the level of the reservoir by 30 feet. That is, they are sacrificing the water storage function of the dam, the main reason it was built by the Water Department, to try to avoid another emergency overflow when rains come Wed.

In 2005, three environment-oriented organizations filed a report with a Federal agency that the emergency spillway is unsafe unless they build a concrete channel for the water. But that would cost the 19 million people in Southern California who use the water $100 million to remedy, so it was not done. During the first day, estimates to repair the damage done to the spillways were $100-200 million. And that figure will only go up. Basically, in 2005 people were advocating that the second spillway, in fact, be an auxiliary spillway instead of an emergency spillway. The director of the California Water Resources Department, when asked about the 2005 report said he was unaware of that report! So did the committee that decided to use the emergency spillway have just political appointees? Were there no hydrologists and engineers on the "experts committee" who had studied the dams construction and history? Had no one researched were the bedrock is? How many other California dams are built so poorly?

The "experts" also did the classic evacuation error that others learned to avoid with hurricanes --- they told everybody at the same time to get out of town. In this case they used the efficiency of a Twitter to create an even bigger traffic jam. And they went from "don't worry, everything is safe" before the evacuation order to "we have no idea when it will be safe and you can go back to your homes" after the order. In fact, they increased the order from 125,000 people to 200,000 people. [My wife told me Tuesday evening that she saw a blurb on the web that they were finally allowed to go back to their homes.]

I read years ago an article about how the levees protecting Sacramento are old and need to be upgraded. I wonder if any upgrades were made. If a 30-foot wall, let alone a 200-foot wall, of water was unleashed, a reporter indicated their levee system would be "tested."

A February 26, 2017 summary of the spillway issues including some speculations as to why it failed in the first place.

An article with 22 photos including repair work  on the emergency spillway.

Update: The main spillway design capacity was 160,000 cfs. [see the video below] The expense of dredging the channel and patching the spillways has already cost $100m. They are still trying to figure out what the permanent fix would be, let alone its cost. The CDWR choose not to spend $0.5m to fix (grout) the spillway and $4m to line the channel of the emergency spillway with concrete when these issues were brought to their attention.
(new window)


This video indicates that it broke where they did repairs in 2014. I'm also confused about why they are ignoring the breach over the parking lot.

2019 Update: I followed blancolirio's videos concerning this disaster (and some other topics) because he deals with facts rather than hype. He got started with these videos because he lives in the area and was doing videos from his airplane such as fire fighting. This disaster was a natural subject for his airplane reports. His knowledgeable questions during water department press conferences earned him the respect of the water department and construction officials, and he has been given private tours. He has videos of those tours and periodic construction update videos. I include one of this more recent reports here so you can see how much concrete was deemed necessary to make the emergency spillway safe. What you don't see is the expense of the secant wall at the foot of the emergency spillway to avoid cutback erosion. It appears they went from way under engineered to over engineered.

(new window)



(new window)






No comments:

Post a Comment