The Conundrum of the Buffalo Bayou Dams
Why so much water for so long in Buffalo Bayou?
May 26, 2016
The water in the normally empty reservoir had dropped only a few feet by the time we stood on the earthen dam looking down at the dark, opaque blue-gray surface. After almost a month, the rippling water below was still some twenty-three feet deep, and extended as far as we could see along the thirteen-mile long dam and far into the thousands of acres of flooded woods.
It had taken only a little more than twenty-four hours for the rains that began on April 18 to fill the vast flood control reservoirs in west Houston with a record amount of water: a total of more than 206,000 acre feet, a massive amount of water. Imagine 206,000 acres covered in a foot of water. Enough to cover more than eight times the acreage of both reservoirs to a depth of one foot. That much water would take an estimated four weeks to drain, according to reports at the time.
But that was only if there was no more rain. There was more rain, and it was taking much longer. The reservoirs, vast wooded parks with recreational facilities and nature paths, are still draining. As of May 24, the combined total of the two reservoirs was still about 90,000 acre-feet, down to a little less than half.
And Buffalo Bayou was still flowing high and fast, higher and faster for longer than ever before. Property owners upstream had flooded and property owners downstream who had hoped for more moderate flows were instead seeing long-standing trees falling into the fast-flowing stream, banks eroding, sediment collecting, debris causing water to back up onto their property.
Why was this happening and is there a way out of it?
Rapid to Rise. Slow to Drain.
Not since 1992 had the water been so high behind the two federal dams that protect the city of Houston from catastrophic flooding downstream on Buffalo Bayou. In fact, until recently, most Houstonians, even those who grew up here, were probably unaware or only vaguely aware that there are dams that prevent the center of the city, including downtown, from massive flooding.
The US Army Corps of Engineers, which built the dams in the 1940s, claims that without the dams the April 18 Tax Day flood would have caused “$5 billion in damage and flooded 24,000 homes and businesses,” said Richard Long, supervisory natural resources manager for the Corps’ Galveston District during a recent visit to Barker Dam.
Both dams were built in response to major flooding in downtown Houston in 1929 and 1935, flooding that also prompted the creation of the Harris County Flood Control District. Interestingly, the reservoirs were not excavated, pointed out Long. The land is naturally if slightly slanted towards the gulf. From the western edge of government-owned land in Addicks Reservoir to the bottom of the dam outlets, the drop is 35.5 feet. The drop in elevation in Barker Reservoir is 25.2 feet. A tilted tabletop. With gulleys and ravines, creeks, rivers, wetlands, and some precious remaining riparian forests.
Buffalo Bayou, which originates west of the dams in the Katy Prairie, flows for 53 miles through Barker Reservoir, through parks and well-to-do neighborhoods and downtown Houston, past more parks and much older, working class neighborhoods and industrial areas, becoming the Houston Ship Channel and eventually entering Galveston Bay. Along the way, numerous creeks and large streams flow into the 18,000-year-old bayou, known as the Mother Bayou. These tributaries include Mason, Stoney, and Spring Branch creeks, and Niemans, White Oak, Brays, Sims, Hunting, Greens, and Vince bayous. Bear Creek, South Mayde Creek, Langham and Horsepen creeks flow through the Addicks Reservoir and join Buffalo Bayou below Barker Dam.
The original 1940 plan was not just for two dams on Buffalo Bayou, however. There was also to be a dam on White Oak Bayou and a levee on Cypress Creek to the north, where there was major flooding on April 18. There were also to be two major canals: one on the north feeding into the San Jacinto River and another on the south that emptied into Galveston Bay. The plan was ignored, wisely or not, as was a much earlier 1913 plan created for the Houston Park Commission by landscape architect Arthur Comey (see page 53) calling for woodland parks along all the bayous extending for some four to six miles through the city.
The Problem Will Probably Get Worse
The dams enabled development close to the bayou. The charming meanders and majestic trees that naturally flourish along the banks attracted developers who built residential subdivisions, as well as office buildings, highrise towers, and parking lots. Development on the bayou and in the prairie upstream and downstream has also increased impermeable surface, causing faster, more concentrated runoff into the reservoirs and into the bayou. (Flooding below the dams now happens because of that fast, heavy runoff from streets, buildings, parking lots, and other paved or hardened surfaces. And mostly it’s flooding that happens before the stormwater gets into the bayou.)
Heavier, more concentrated rains, dumping more water in one place all at once, also have been increasing and are expected to continue to increase, according to Texas State Climatologist John Nielsen-Gammon.
There will be more water rising faster.
And it’s not hurricanes.
“Hurricanes have not really been what has hit us over the years,” said Long, who was wearing a long-sleeved oxford blue shirt embroidered with “US Army Corps of Engineers” in red over the pocket. A civilian employee like many of the staff, Long has been working for the Corps for 38 years – 35 of those years at the dams.
“Houston does not have a dry season,” he said.
The Tax Day Flood
The water rose high enough in the 13,108-acre reservoir behind Addicks Dam north of Interstate Highway 10 that by the afternoon of April 21 it was backing up into the streets of Bear Creek Village, the residential neighborhood built rather unwisely close to the reservoir in the 1970s, some twenty-five years after Addicks Dam was completed. On April 18 the heavily burdened skies had dropped some 17.5 inches of rain in 24 hours on parts of northwest Harris County above the dams. Wild animals – deer, coyote, alligators, snakes – were fleeing the rising waters in the forests of both reservoirs, some 25,000 acres of federally-owned land in total. Harris County workers were attempting to rope and rescue Buffy the Bison, swept up in the impounded waters that flooded the 2,154-acre Bear Creek Park and its small zoo and community center inside Addicks Reservoir.
By the evening of April 21 the rains had stopped, at least temporarily. Staff of the Corps of Engineers walked out to the dams and onto the gray metal platforms jutting out over the reservoir lakes and began pushing the green buttons that open the gates – five in Addicks and six in Barker — that release water held back behind the dams. Water that smelled like sewage, though it’s not. The putrid smell from the bottom of the reservoir pools is natural. “It’s decomposing vegetation,” said Long. “It’s just a natural process.”
A Balancing Act
And thus began a lengthy and complicated balancing act: releasing enough water to drain the reservoirs fast enough to make storage room for future, perhaps imminent storm water that had to be impounded to prevent flooding downstream (the primary purpose of the dams), while not flooding homes upstream — and yet without releasing the water so fast that it causes more flood damage to homes and property downstream. Monitoring the weather. Closing the gates when it’s raining; opening them when the rain stops. Dealing with complaints from property owners up and downstream.
One might expect the control center for the dams to look more like NASA with big colorful high-tech screens for monitoring the weather, the rising waters, the submerged conduits. It doesn’t. The Addicks Field Office on Highway 6 South is a small, modest building, though strongly barricaded, with ordinary long tables, simple portable computers, dry erase boards, old maps, and a coffee room. The parking lot floods in the rain. Inspectors in red Army Corps t-shirts who’ve just been patrolling and checking the dams in a truck (the dams are inspected 24/7, said Long) were sitting together at a table looking at small laptop screens.
“We are talking to the National Weather Service and Flood Control hourly,” said Long. Around the time of the Tax Day rains there were “maybe thirty people from the Galveston District office” crowded into the small building, he said.
Long has also been talking to reporters, answering emails and phone calls, and even talking to people knocking on the locked door of the office wanting to know what was happening with the dams.
The Known Unknowns
There’s also the unknown of having the reservoir levels rise higher than they ever have before. The maximum pool level of Barker Reservoir – the level at which water begins to spill around the ends of the dams – is 104 feet above sea level, or about 34 feet above the bottom of Buffalo Bayou’s streambed and the gate outlets. The Barker pool of record in 1992 is 93.6 feet, and on April 21 the reservoir hit 95 feet. The maximum pool of Addicks is 108 feet above sea level or 40.5 feet above the bottom of the outlets. On April 21 the level of Addicks reservoir hit 103 feet. The 1992 pool of record was 97.64 feet.
“It was a record pool by far,” said Long. “It doubled the record of acre-feet from the prior pool of record in Addicks.”
In 2009 the dams were labeled “extremely high risk,” a classification based in large part on the fact that the dams protect so many homes, businesses, and people in the nation’s fourth most populous city. The Corps identified two areas of concern: voids under the conduits and seepage around the conduits and ends of the dams. The Corps did some repairs, and the dams are now operating normally, said Col. Richard Pannell, district commander, in a March 9, 2016, public meeting. But the plan is to build entirely new conduits for the dams, a $72 million construction project that has been delayed by the rains.
Managing an Increasing Amount of Water and the Potential for Failure
Much attention has been focused on the “extremely high risk” designation and the seepage problems. Seepage is in fact a major cause of dam failure. Long, during a truck ride down the gravel road on top of Barker Dam, pointed out the many small pipes stuck in the ground on and around the dam. They were piezometers that measure changes in the pressure of the groundwater and detect seepage through the dams.
But seepage is only one cause of dam failure. Overtopping, water flowing over the top of a dam, is the most frequent cause of dam failure in the United States. Long said the Houston dams were designed not to overtop. “They will never overtop,” he said. Water instead flows “around the ends of the dams and the emergency spillways.” So far the reservoirs have never done that.
Operational failure, including debris blockage, gates getting stuck, and a “reluctance to open the gates and flood people out” are other frequent causes of dam failure.
When to Open the Gates
Property owners on Buffalo Bayou downstream were hoping for a moderate release rate from the dams after the Tax Day rains that would spare their trees and banks (and parks) from further damage. Something that did not exceed 2,000 cubic feet per second (cfs) as measured by the US Geological Survey gauge at Piney Point.
It was not to be. On April 18, during the height of the storm, when the dam gates were closed, the flow in Buffalo Bayou reached nearly 7,000 cfs, as measured by the gauge at Piney Point. (The Memorial Day flood on May 26, 2015, exceeded 7,000 cfs and reached 8,500 cfs, according to the Harris County Flood Control District, page 9.) As of this writing, combined releases from the dams, measured by the Piney Point gauge, have exceeded 3,000 cubic feet per second for longer than even after the Memorial Day flood, the first time the Corps deliberately raised the release rate to 3,000 cfs, and frequently have reached 3,700 cfs. Homes downstream are expected to flood above 4,000 cfs.
Don Jones lives on the bayou downstream and lost trees during the 3,000-plus cfs releases that continued for some eleven days after the Memorial Day floods. (Overall it took seven weeks to drain the reservoirs of water from the Memorial Day rains, page 10). Jones was one of those who hoped the releases from the dams following the Tax Day rains would not exceed 2,000 cfs, which is the Corps’ normal maximum release rate. Like many others Jones was disappointed. “Right now I have a tree that is still standing in the bayou 30 feet from dry land,” he wrote in a comment to our website. “It won’t be there for long. When the Corp is finished releasing water we will see a lot more erosion than last year.”
Long said the Corps normally tries to limit releases to a maximum of 2,000 cfs. But at 2,000 cfs “it would have taken forever” to get rid of the water behind the dams, he said. To be exact, without any further rain, it would have taken 52 days and perfect weather to get rid of 206,000 acre feet of water behind the dams. But there was more rain, which causes the Corps to close the dam gates and adds more water to the reservoirs.
So instead we have seen flows above 3,000 and up to 3,700 cfs in Buffalo Bayou for nearly five weeks.
“Our goal is to keep the reservoirs empty,” said Long.
Somebody is Going to be Inconvenienced
On the afternoon of April 21 the Harris County Flood Control District issued a warning to residents in the Bear Creek Village subdivision adjacent to Addicks Reservoir that rising water from the reservoir would likely flood their streets. Streets and homes did flood. But Long insisted that the flooding of homes was not caused by water from the reservoir but by poor drainage. “We did not put any water in any houses anywhere,” he said. “All the flooding in houses up there was the result of heavy rains and runoff trying to get into the reservoir.”
Richard Hyde, a geologist who lives in the neighborhood, agreed. His home and garage were badly flooded, along with many others, by a storm drain belonging to Utility District 6, covered in rebar, chicken wire, and debris, that blocked rainwater in the drainage ditch from getting to the reservoir. That was the responsibility of the utility district, said Hyde, and he wasn’t happy about it. As a result of the blocked utility district drainage ditch, there was waist-deep water in the street in front of his house during the height of the flooding, and water in the street for a week, he said. His backyard adjacent to the reservoir remained dry. “We never were flooded by the reservoir,” he said.
It will keep raining. Developers will keep developing. Drains will be blocked. And the waters will keep rising. Eventually the limits will be tested.
What’s the solution?
The Corps is planning to study these issues in what’s called a Section 216 study. Though the study is required by law, it is also contingent on federal funding from Congress. Among other things, the study is expected to address the eventuality of the reservoirs reaching maximum capacity and flowing around the ends of the dams, as well as “non-breach flood risk and potential operational concerns upstream and downstream.” Page 30.
“The first thing they’ve got to do is look at the big picture,” said Long as we drove back to the field office. “There’s not going to be one solution. There’s going to be multiple solutions that we have to look at,” he said.
“We have put ourselves in a situation here that forces some drastic action each time we have a big rainfall,” said Long.
“Somebody is going to be inconvenienced. Either the people upstream or the people downstream. And the answer will also be an inconvenience.”