What causes Houston's flooding problem?

HOUSTON – Two university professors and the U.S. Army Corps of Engineers say several factors have contributed to the recent flooding in the Houston area, but say the biggest cause is the enormous amount of development in Houston over the years.

"When we put concrete down, when we build drainage channels, we concentrate that water and dump it off the land where it used to be stored, we push it downstream on ourselves. That's been the story of Houston development,” said Rice University civil engineering professor Jim Blackburn.

He says that prior to development, areas west of Houston in the Cypress, Addicks and Barker watersheds held large amounts of water that now is funneled into streams and the massive holding pools of Addicks and Barker reservoirs.

"There used to be natural prairie here. It was full of small wetlands areas that were depressions. We ponded tremendous amounts of water," Blackburn said.

Over decades those prairies have disappeared.

In the 1930s, area-leaders knew Houston had a problem with where to hold water after large-scale rains.

The government bought up land, mostly farmland, north and south of the present-day Katy Freeway near Highway 6. Two giant reservoirs were created: Barker and Addicks.

"When Congress authorized these projects, the goal was to reduce the potential for flooding along Buffalo Bayou and all the way to the ship channel,” Richard Long, with the U.S. Army Corps of Engineers for Galveston and Houston, said.

Long says the Barker and Addicks projects performed properly during the storm on April 18.

"We prevented over $5 billion dollars in damage and 24,000 homes and businesses were not flooded as a result of these projects," he said.

Long says no homes were flooded as a result of holding water back in Addicks and Barker reservoirs.

He says homes that flooded in Bear Creek Villages above the reservoirs, for example, did so because new development forced water into fast-moving streams.

"The problem that occurred on the day of the storm was water trying to get into reservoirs via the streams: Langham, Horsepen, Bear Creek, Mayde or Buffalo Bayou. They were overtaxed by the amount of water that fell from the sky," Long said. "It's not magic that it happened. It's just a matter of time when it was going to happen."

These experts say the problem isn't going away.

The areas in purple were in the 100-year flood plain in 1996. Since then, areas in the flood plain have grown and now include the areas in yellow too.

A 100-year flood possibility means there is a 1 percent chance that much rain will fall in any given year.

Rice University professor Phil Bedient says we can expect more massive floods.

"There is no question. If you look at the last 15 years since Allison, we’ve had seven major floods in the Houston region. That's one every other year and that's never happened," Bedient told investigative reporter Jace Larson.

If you have a tip for investigative reporter Jace Larson, email or text him at jlarson@kprc.com or 832-493-3951.