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Can our dams handle the load?

Pretty important question, wouldn’t you say?

The state climatologist is warning that Texas dams will become less able to withstand extreme weather events like Hurricane Harvey, which are expected to occur more frequently as the earth’s atmosphere and oceans warm in coming years.

Dams are designed with a wide margin of safety and are meant to withstand extreme, worst-case scenarios that are never expected to happen. But what stunned state climatologist John Nielsen-Gammon and other weather experts was that Harvey exceeded or matched the preposterous amounts of rainfall that dams in Texas are built to hold back.

“The probable maximum precipitation amount should never be reached,” said Tye Parzybok, the chief meteorologist at MetStat, a Colorado-based company that helped Texas calculate the rainfall amounts. “It should never get close to it.”

After Harvey, dam regulators will have to recalculate the maximum amount of water that dams should be capable of holding back, said Nielsen-Gammon. Climate change means that powerful storms are bringing vastly more rain than they did a century ago, he said.

“I’m not saying they’re unsafe,” said Nielsen-Gammon of Texas’ dams. “They will be less safe than they were designed to be.”

On the one hand, Harvey was an extremely unlikely event; by some estimates, a one in 500,000 year event. Nobody plans for that, and for good reason. On the other hand, if it could happen once it could happen again, and the consequences of a dam failure would be catastrophic. Even before Harvey, it was the case that the capacity of the Addicks and Barker reservoirs was declining due to the buildup of dirt and sediment over the years. Surely this is something that can be addressed.

U.S. Rep. Sheila Jackson Lee, a Houston Democrat, is calling for the replacement of the aging Addicks and Barker dams that spilled over during Hurricane Harvey.

“As we recover and rebuild from the devastation caused by Hurricane Harvey, it is crucial that we also learn from this catastrophic storm and prepare for the next one,” she said in a statement. “A critical takeaway is that our infrastructure is ill-prepared for the ferocity of thousand-year weather events and record-breaking rainfall.”

[…]

Jackson Lee, a senior member of the House Homeland Security Committee, is pushing provisions in the Energy and Water Appropriations Act that would provide $3 million to fund the Army Corps of Engineers’ Houston Regional Watershed Assessment Flood Risk Management Feasibility study, as well as $100 million for flood control infrastructure.

Seems like a reasonable approach to take. What do other members of Congress that represent the Houston area, as well as our two Senators, think of this? Before you answer that, consider this:

“Addicks and Barker were not designed to impound large pools behind them for an extended period of time,” an Army Corps official wrote in a 2011 email, which was made public through a lawsuit the Sierra Club filed against the Corps over a road project near the reservoirs. “These larger and longer lasting pools … [are] increasing the threat to both dams.”

Another Corps document, this one from 2010, shows that the agency was using terms like “risk of catastrophic failure” for the dams for flood events much smaller than what Houston experienced during Harvey.

That 2010 “interim reservoir control action plan” sets what it calls “maximum pool” levels for Addicks and Barker at elevations well under 100 feet, levels that could be expected during a 25-year storm — which has a 4 percent chance of occurring in any given year. Such a storm is about 30 times smaller than the rains generated by Harvey.

“The purpose of this … is to reduce the risk of catastrophic failure by [releasing water from the dams] quicker and increasing embankment surveillance,” the document says, adding that at 25-year levels, the dams “need to get additional attention.”

The document, which also became part of the 2011 Sierra Club lawsuit against the Army Corps, doesn’t specify what the true risk of dam failure might be at such levels. It also doesn’t say what exact actions the Army Corps would take when water reached that point.

[…]

“I think that the documents, and I think that the issues, are clear,” said Jim Blackburn, a Houston environmental lawyer who filed the Sierra Club lawsuit. “The consequences of failure are horrific, and it would be truly frightening to the public if they really knew what the worst-case scenario looked like.”

Blackburn said the failure of the Army Corps to make the 2010 document public is just one example of the agency’s hesitance to address the risk of a dam breach.

“I think they have not wanted to have an honest conversation about it, for some reason.”

Matthew Zeve, the Harris County Flood Control District’s director of operations, said he had not seen the 2010 document before the Tribune sent him a copy. But he said he didn’t think the document expressed concern about the dams actually failing at such low water levels but rather indicated a “trigger” for when the agency should be continuously monitoring the dams and doing whatever it can to diminish risk.

“It’s not, ‘Oh, we think it’s going to fail,’” he said, stressing that he was not speaking for the Corps but offering his personal interpretation of the document.

Yeah, that’s not very reassuring. Let’s start investing in better flood mitigation infrastructure, shall we?

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2 Comments

  1. voter_worker says:

    In 1972, a previously unheard-of amount of rainfall in the Black Hills resulted in a flash flood which devastated Rapid City with mind-boggling property destruction and deaths of residents. The community responded by banning development and re-building in the destroyed areas. Yet, as the linked article indicates, decades later the developers haven’t given up trying to build projects in the flood plain. The old paradigm in Harris County is not going to go down without a fight. http://www.npr.org/2012/06/08/154576917/disastrous-s-d-flood-caused-national-wake-up-call

  2. Flypusher says:

    “Blackburn said the failure of the Army Corps to make the 2010 document public is just one example of the agency’s hesitance to address the risk of a dam breach.”

    This is why I’ve asked whether full risk disclosure was made to people who bought houses in the Memorial area.