Early Flood Warning System "Online"
For Four Years, Has Provided Flood Warnings to TMC Area

An "early warning" system, that for four years has provided the Texas Medical Center/Rice University area with advance notice of impending flood conditions, performed as intended the evening of June 8, as Tropical Storm Allison began depositing what would become the highest level of rainfall ever recorded in the Texas Medical Center. But the system, designed to provide as little as two and as much as four hours' warning against imminent flooding, could not prevail against the enormous amount of rain dumped on the area in a very short period of time.

"No current technology exists that could have provided adequate warning of what was coming. Events unfolded so quickly that there was no way humanly possible to predict this type of flooding, which statistically occurs only once every 500 years," said Dr. Philip Bedient, a Rice University professor of Environmental Engineering who designed the early warning system. Developed for the TMC area in 1997 and 1998, the Rice University/Texas Medical Center Brays Bayou Flood Alert System, accessible at http://www.floodalert.org, combines radar, the Internet and extensive knowledge of Brays Bayou to provide several hours' warning of flood conditions. Prior to the system's invention, the area had only a half-hour warning before flooding hit.

"The early warning system can let us know whether to cancel surgeries, re-route ambulances, or secure necessary resources," said Dr. Richard E. Wainerdi, president and CEO of the Texas Medical Center. "Technology can provide assistance, however, it can't control events."

The flood alert system uses Next Generation Radar, or NEXRAD, which is 10 times more accurate than traditional radar and can be translated into actual accumulation of rainfall for a very specific region every six minutes, to produce a "real-time" model for flood prediction.

Radar images are updated in realtime and placed on the Flood Alert System Web site. Data from the radar is extracted and used to create a graphic representation that predicts peak flow in the bayou, and alerts viewers to the information while they are viewing the Web page.

The early warning system provided definitive data about weather conditions related to Tropical Storm Allison until just after 2 a.m. on Saturday, June 9, when Rice University's Internet Service Provider went down due to flooding. However, by 2 a.m., the flooding had already begun in the Texas Medical Center.

"The bulk of the flooding occurred between midnight and 2 a.m. on Saturday, June 9, when 8.5 inches of rain poured down on an already saturated Texas Medical Center," said Dr. Bedient, who refers to the Allison flood as "one-tenth Noah."

"Instead of raining 40 days and 40 nights, it rained four days and four nights. All told, Allison dumped approximately 14 inches of rain on the Texas Medical Center in a nine-hour period. This much water in that short of a timeframe makes flooding inevitable," he said.

Dr. Bedient said Brays Bayou floods when 6 to 8 inches of rain falls in 8 to 12 hours or less.

In comparison, the entire Brays Bayou region was able to handle 12 to 15 inches of rain before reaching flood levels in the 1960s. Why can't the bayou area manage rain like it used to? The reason, said Dr. Bedient, is the rapid development of the entire Houston area that has occurred during the last 40 years, leaving no place for urban runoff. Combine this with building elevations that have dropped after decades of subsidence, and it stands to reason that the problem is getting worse.

The Texas Medical Center campus is at risk for flooding because it is proximal to Brays Bayou and because two 15-by-15 foot box culverts drain an area known as the Harris Gully and run underneath the Texas Medical Center and Rice University campuses. The Harris Gully box culverts carry rain and runoff water from neighborhoods north of Highway 59 (as far northwest as Westheimer at Buffalo Speedway) southward to lower elevations, moving steadily downhill as they continue under the Texas Medical Center and Rice University campuses. Ultimately, the culverts empty into Brays Bayou along MacGregor Way, across from the Hospice at the Texas Medical Center.

It is here that serious problems develop when the bayou is full of water.

"A full bayou restricts flow from the box culverts, which forces the water in the culverts to back up into the storm drains that are strategically placed around the Texas Medical Center. Manholes begin to pop off, water flows into the streets, and flooding occurs," explained Hank Rietz, Texas Medical Center vice president in charge of emergency preparedness.

To envision how the drainage system works, think of the Harris Gully drainage system as a bathtub. Water drains from the slightly higher back of the bathtub (the areas north of Highway 59) down to the lowest point of the tub, which is the Texas Medical Center. The drainplug is the point at which the Harris Gully culverts empty into Brays Bayou. Just as water backs up into your bathtub if a clogged pipe prevents it from draining, water backs up into the streets if a full bayou prevents it from draining.

"Because street flooding in the Texas Medical Center is directly related to the water level in the Harris Gully box culverts, it is extremely important to monitor the level in the box culverts during heavy rains," Rietz warned.

This is accomplished with a camera known as the "BayouCam," which is mounted on an outdoor pole strategically situated between the Ronald McDonald House of Houston and the Hospice at the Texas Medical Center. Every five minutes, the BayouCam takes a picture of the juncture where Brays Bayou and the Harris Gully culverts meet, providing information about the bayou's water level and the status of water flow exiting the culverts. One minute later, this image is posted on the http://www.floodalert.org Web site for all to see. With this critical information, each Texas Medical Center institution, by monitoring the early warning system, can activate flood prevention tools at their disposal.

In 1976, a major flood hit the Texas Medical Center, and until Allison, the flood of 1976 was thought to be the worst ever in the area. After that experience, the TMC institutions took proactive preventive steps. With the help of the Federal Emergency Management Agency, they constructed flood-protection systems including pumping stations, flood gates and doors, retaining walls and other mechanisms to protect critical areas within their institutions. Such protective measures were particularly important for those institutions connected by underground tunnels and with access to underground garages, Rietz said. These devices were designed to provide flood protection one foot above the water level of the 1976 "worst ever" flood.

Twenty-five years later, the unprecedented rates at which the rainfall and runoff occurred during Allison caused the water to far exceed the height of the protection devices that were designed after the 1976 flood.

A coordinated effort involving various agencies of government, Texas Medical Center institutions and the management of the Texas Medical Center is under way to identify steps that can be taken to lessen the severity of flooding in the Texas Medical Center area in the future. Upcoming articles in TMC News will report on developments as they occur.

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©2006 Texas Medical Center

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URL: http://www.tmc.edu/tmcnews/08_15_01/page_02.html