Houston dams are old, beat up and a vital line of defense

Richard Long drove along empty roads that were almost impossible to see, thanks to an unrelenting downpour and early morning darkness. He tried to follow the yellow line on FM 1093 but found himself drifting into turn lanes.

Long was the first to arrive at the Army Corps of Engineers' small office off Highway 6 in west Houston, where he had worked for 35 years. As he waited for his team on April 18, still before 5 a.m., he worried about what the water would do to Addicks and Barker dams, each seven decades old and rated seven years ago by the Corps among the nation's six most unsafe dams. Major repairs are ongoing.

At daybreak, Long went out to check on them, as pounding rain drowned out all other sound. Water rushed into the reservoirs faster than he had ever seen, transforming acres of woods and parks into lakes.

Later that day, the Corps' district commander came in from Galveston, followed by a dozen volunteers. They would work 12-hour shifts, walking along the dams and riding in UTVs, searching for movement and wet spots, checking groundwater levels.

More Information The series so far Part 1: Houston is losing ground Part 2: Living in a swamp Part 3: Looking for answers Part 4: A crippling choice Part 5: More concrete, less prairie Read these stories online at houstonchronicle.com/swamped

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The rain finally relented, but the water in the reservoirs kept rising. Every day. For seven days.

On April 23, the water reached 102.65 feet above sea level at Addicks, a record. Two days later, at Barker, the water level hit 95.24 feet, another record. Together, at their peak pools, the reservoirs stored 6.8 billion gallons, enough to fill NRG Stadium 101 times over. The last time the reservoirs collected close to that much water, it was after months of repeated storms. This time, it took only one big one.

The water would not completely drain for more than two months. Holding that much water, for that long, is not what Houston's dams were designed to do. Addicks and Barker were built to protect the heart of the city by controlling the flow of water along Buffalo Bayou. Things haven't gone as planned.

Repairs totaling $72 million are underway, and the Corps says there is no imminent risk of failure, but it realizes the need for a longer-term solution.

What's at stake is the safety of the nation's fourth-largest city. If the dams failed, half of Houston would be underwater. Under the worst scenario at Addicks, property damages could reach $22.7 billion and 6,928 people could die.

"Failure is not an option for us," Long said.

Addicks and Barker were six decades old, with a long history of seepage and erosion, when the Corps evaluated their condition in 2007. Once positioned far from downtown, they were now surrounded by houses and highways. Some residences sat within the reservoirs, which straddle the Energy Corridor along Interstate 10 and west of Beltway 8.

Development upstream was sending more runoff into the reservoirs, which were filling faster and storing water for longer. Nine out of the top 10 pools for both reservoirs have occurred since 1990.

"Every piece of concrete that's poured upstream is going to have an impact on these reservoirs. Every square inch," Long said.

The evaluation found many aspects of the dams - the embankments, the conduits, the water control structures - were "probably inadequate" for an extreme storm, inspection reports show.

Ground-penetrating radar scans soon revealed a more precarious situation. Voids had formed beneath the conduits on both dams. Large cracks extended through the conduits and spillways, which showed signs of movement. In 2009, Addicks and Barker advanced to the Corps' worst safety classification, rating a 1.

Only four other dams - out of hundreds across the country - received that rating. None was near a city as big as Houston.

By 2012, the Corps had filled the voids with polyurethane and cement grout, a temporary fix. Filters were installed to control seepage. Inspections were heightened.

The agency also calculated major ways, six at each, that the dams could collapse.

The deadliest scenario for Addicks involves the outlets failing as the pool rises to 106 feet, producing the staggering loss of billions in property and thousands of lives after water submerges downtown, west and south Houston and the Texas Medical Center.

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Houston's dams were born of necessity in the first part of the 20th century.

In May 1929, flooding caused $1.4 million in property damages to a city of just under 300,000. Houstonians rebuilt and recovered, but an even bigger storm hit in December 1935.

Buffalo Bayou transformed from meandering stream to roaring river, at one point rising 14 inches an hour. Currents swept away people, rescue boats and a three-story brick building at Milam and Commerce. At the Capitol Street Bridge, waters typically 6 feet above sea level rose to 52 feet. The storm caused eight deaths and $2.6 million in damages ($45.7 million in today's dollars) and brought the Port of Houston to a standstill.

The next year, city officials started formulating flood-control plans with the Army Corps of Engineers. By 1940, a $32 million plan had been refined to include three reservoirs - Addicks, Barker and White Oak - and a levee to prevent Cypress Creek from overflowing into Addicks. Two large canals would divert waters from the reservoirs north and south of downtown. Upper Buffalo Bayou would be straightened to enable faster flow.

At the time, the Corps anticipated most floodwaters would drain within a few days.

Barker Dam was finished by February 1945. Addicks, adjacent to Barker, followed in late 1948. Together, the dams stretched for 25 miles and encompassed about 26,000 acres once used for ranching and rice farming. They were hailed as two of the longest dams in the world.

Both included earthen embankments formed with native sand, silt and clay. Each had five conduits - openings through which water would be conveyed onto concrete spillways and down the bayou. Designs called for one conduit on each dam to have a metal gate directing the output of water. The rest would be ungated, allowing water to exit uncontrolled.

The city still faced bouts of flooding, but the dams performed as expected. Homes and businesses sprung up along the bayou.

"There's a lot of things that allowed Houston to develop," Long said. "These reservoirs are number two on the list. Number one is air conditioning."

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Over the next 50 years, development persisted, and the Corps found itself unable to control what was happening around the dams.

The remaining components of the 1940 plan - the third reservoir, the levee and the canals - failed to materialize. Land costs became prohibitive as people moved in.

The Corps then proposed deepening and lining Houston's bayous with concrete to allow for the release of more water, alleviating pressure on the reservoirs. When environmentalists protested, that plan was abandoned, too, after only a few miles had been lined.

Residents along the bayous soon grumbled about their yards flooding as water was released from the reservoirs. They wanted the other conduits gated, a move engineers worried would put the dams at risk of being washed away. But by 1963, the change was made.

By the 1970s, the dams were storing bigger pools, for longer, putting more stress on the foundations.

Houston's "crummy soils" didn't help, Long said. The silt and sand used to construct the dams washed away easily. And the reservoirs and dams were sinking, a phenomenon known as subsidence. Over time, settlement lowered the tops of the dams by up to 3 feet.

In 1977, the Corps started seeing signs of seepage - water leaking into the foundations.

All dams leak to some extent, but it becomes problematic when water erodes soil within the embankment. If enough soil gets carried away, it can lead to cavities and sinkholes or piping, paths that allow water to flow freely through the dam. If enough water gets through, the dam can fail.

The Corps installed miles of slurry trench, walls to prevent seepage and water flow. It also raised the tops of the dams to protect against a massive hurricane, and put in barriers to stabilize the embankments and screens to catch eroding material. But the trench did not extend across the embankments, leaving areas around and beneath the conduits vulnerable.

Other Corps dams and levees across the country faced similar problems, but the agency's shortcomings weren't highlighted until Aug. 29, 2005.

That's when the storm surge from Hurricane Katrina breached New Orleans' Corps-built levees in more than 50 places. Walls of water barreled into roads and homes, inundating three-quarters of the city. Almost 2,000 drowned.

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Just two months before Katrina, the Corps had begun a massive undertaking: evaluating its hundreds of dams nationwide. Many were at or beyond their 50-year life expectancies. The review would identify the dams most at risk and prioritize repairs.

Katrina drove urgency and was sobering for an organization that could be overconfident, said Jeffrey McClenathan, a retired hydraulic engineer and coordinator of the Corps' four-year review.

McClenathan said the Corps looked not only at the risks but also the ramifications of failure, which it hadn't done before.

The Corps' evolution was a necessary and important step, said David Bowles, former director of the Institute for Dam Safety Risk Management at Utah State University. He helped design a version of a program the Corps uses to model failure scenarios.

"They are now able to be so much more effectively than the way they were before," Bowles said.

But even on dams like Addicks and Barker, progress is still patchwork, and slow-going.

A contract was awarded in August 2015 for the replacement of the water control structures and conduits, 400 feet from the existing ones. Work began in February but shut down when the reservoirs were submerged in April. Before the delays, the finish date was in 2019.

After Tax Day, subsequent downpours added water to the reservoirs a half-dozen times, prompting the Corps to double normal release rates to empty the swollen reservoirs as quickly as possible. The water control structures vibrated as they dispelled murky water onto the spillways and down Buffalo Bayou, carrying away trees and soil. Some residents downstream feared the banks would completely erode.

Emptying the reservoirs is similar to draining a bathtub. The tub fills up. Then, the Corps pulls the stopper. The goal is to keep the water draining at a steady but manageable rate, while never letting the tub overflow.

If a big enough storm threatened the integrity of the dams and the Corps had time to react, it could pull the plug, purposefully flooding residents downstream. The Corps also can impound water on more land than it owns, so it could flood properties behind or beside the reservoirs. Flooding some would be better than failure, Long said.

"We've got to make sure we protect the city of Houston as a whole," he said.

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Over the years, some argued the Corps allowed development to go too far. In 2011, the Sierra Club sued the Corps and state agencies over construction of a Grand Parkway segment northwest of the reservoirs. The complaint alleged the Corps knew another highway would increase runoff, impacting the deteriorating dams, yet still approved a permit for construction - an "irrational conclusion."

Over email, Long and Corps colleagues privately agreed more concrete upstream would exacerbate existing problems. But ultimately, Corps hydrologists concluded the highway, by itself, would not harm the dams, with appropriate drainage measures.

The Grand Parkway moved forward, but the case may have caught local officials' attention, said Jim Blackburn, an environmental attorney who represented the Sierra Club. He said a multi-year study on the overflow of Cypress Creek into Addicks Reservoir signaled a major step forward.

The study, completed last August, also looked at runoff during major storms and from projected growth. It estimated another 200,000 people would move into the area by 2060.

"It's time for action of a type that we haven't seen previously," he said.

Based on the study, in March the Harris County Flood Control District issued new criteria for developers in the Addicks, Barker and Cypress Creek watersheds. Previous guidelines required developers to address the rate at which water left their properties, but not the volume ultimately draining into the reservoirs, said Dena Green, the study's project manager.

The study offered two ideas for tackling the dams' limited capacity and releases. Both involve building earthen reservoirs to either fully or partially contain the creek's overflow, which sends more than 20,000 acre-feet of water into Addicks during a 100-year storm.

The Corps also is looking to address its encroachment problem.

Project managers, in partnership with the flood control district, are pushing for a federally funded study on the cumulative impact of land changes around the reservoirs, and what would happen if Addicks and Barker became so full that water spilled over the sides, which came close to occurring after the Tax Day storm.

The study would invite long-term solutions, Long said, and "everything will be wide open."

Long plans to retire after the major repairs are completed and leave the worrying to someone else.

For now, he likens the dams to a rebuilt car. He is confident in recent fixes. But he knows there is always the chance, however small, that the next storm will be the perfect storm.