Here's the deal with what could be a terrible threat to Houston: most of the time, it isn't. In fact, it's a 26,000 acre recreational greenspace on Houston's west side. It lies on both sides of the Katy Freeway at Highway 6.
On one side is the Addicks Reservoir. On the other is the Barker Reservoir. Both have dams, but most of the time there is very little water to be held back by either. So the acreage is used for parks and has miles of paved bike trails.
We were well inside the park when we stopped biker John Tucker of Katy who told us he rides here "every day on my lunch break." But what about when it rains a lot?
"This whole thing will be flooded, you can't pass, right here," Tucker said.
What the Dams Do
Even a moderate rainstorm last month created a pool of water but only right up behind the Barker Reservoir dam. That's where we met Richard Long who for 35 years has worked at the dam for the U.S. Army Corps of Engineers.
He took us to the top of the dam gates, unlocked the control panel, and flipped a switch.
"This is the gate operating right here," Long said as an electric motor hoisted the gate upwards inch by inch, allowing the pool of water to slowly drain into Buffalo Bayou.
"We want to get rid of the water as fast as we can so the reservoirs are available for the next rain event," Long said.
What Could Go Wrong
But therein lies the cause for concern: what if that "next rain event" is something really, really big? It's been on the mind of Jim Blackburn, a Houston environmental attorney.
"When you need Addicks and Barker is when it's been raining for a couple of weeks," Blackburn said. "That's what we're worried about, these big storms that follow each other. Where you get two or three or four storms within a couple of weeks period. That's the scary thing."
Scary because with successive storms, the reservoirs wouldn't have time to drain and water would get higher and higher. In the history of the two dams, the reservoirs have never been more than a third full but what if they filled beyond that and the dams failed?
Richard Long, the dams' manager, offers this scenario: "Because of our flat terrain here, we don't have a valley that the flood would go down. It'll spread out over a very large area. It won't be like the horror movies you see where a wall of water is coming down a canyon. It would be very rapidly rising water and cause an extremely large amount of damage and possibly a loss of life."
The Army Corps estimates that a dam failure could cause flooding from Buffalo Bayou and Downtown all the way over to Brays Bayou and the Medical Center. For years, the Army Corp has been monitoring “seepage” of water underneath the dam gates. Those leaks led to the Corps designating the Addicks and Barker dams "extremely high risk" and among the six most critically in need of repair in the nation.
Over 7,000 Hazardous Dams in Texas
The Army Corps didn't provide us with a list of the nation's worst dams. Texas alone has over 7,000 hazardous dams that threaten lives but detailed lists are kept secret by state government which said it can't let such information fall into the hands of terrorists.
The Army Corps has committed $75 million to completely replace the big gates on both Addicks and Barker dams. Work is just now beginning and will take up to four years to complete.
Harris County is also taking action that might reduce the risk. If approved by the county commissioners' court, new rules will require that developers build retention ponds and take other measures to reduce rainwater runoff into the Barker and Addicks reservoirs.
That was one of the concerns of the Sierra Club when it filed suit in 2011 to stop construction of the Grand Parkway. It lies west of the reservoirs and the environmentalists argued that all the new homes, strip malls and offices that would grow up around the new highway would increase runoff and imperil the dams. The lawsuit didn't stop the parkway but the court said those runoff impacts needed to be addressed. One other issue is a concern that the ends of the dams are inadequate should the reservoirs fill up. The Army Corp is continuing to study ways to remedy the problem.
The bottom line for attorney Jim Blackburn is simple and sobering: "Those dams cannot be allowed to fail. No question about it, that ought to be a number one priority."