Flood Alert Provides Lead Time

Flood Alert Provides Lead Time

BY LIA UNRAU
Rice News Staff
Nov. 12, 1998

Intense rainfall from Tropical Storm Frances, which blew into the Houston area on Sept. 11, provided the first test of the Rice/Texas Medical Center (TMC) Flood Alert System, which is now fully operational.

“If the Brays watershed had received about one more inch of rainfall in one hour, the Texas Medical Center would have been in serious trouble,” said Philip Bedient, professor and chair of environmental science and engineering. “This was a good test for the system, and it worked well.”

The flood alert system gives lead time–an extra two to three hours of warning. More than 70 percent of flash flood warnings are issued with less than one hour of lead time and half of the warnings issued provide no lead time whatsoever. In addition, National Weather Service warnings are very regional in scale. The county is the smallest unit over which a warning will be issued, and Harris County contains several watersheds that react to rainfall independently.

The system has been developed and refined over the past year under the leadership of Bedient, along with Rice research scientist Anthony Holder, and graduate students Brian Hoblit and Dawn Gladwell.

The system was created in large part due to concerns of Texas Medical Center President Richard Wainerdi. The TMC sees over 50,000 patients each day, and has a similar number of staff, and must watch for flooding in nearby Brays Bayou.

The system was developed for Brays Bayou, which rises more quickly in response to rainfall than other bayous in the city. It utilizes computer modeling that combines topography, land use, an advanced radar system and rain and stream gauges to track the amount of rainfall and runoff over time.

Using radar estimates of rainfall volumes that come in every six minutes, Bedient, Holder and Baxter Vieux of the University of Oklahoma first calibrated the radar estimates with actual rainfall amounts from past storms, then developed a system that uses the radar rainfall numbers to predict peak flows in the bayou. The system takes into account how the region’s geography reacts to the rainfall. The radar provides the big picture, showing how much rain is coming, where and when, with much more spatial and temporal detail than rain gauges alone.

During the morning of Sept. 11, Holder woke at 3 a.m. and began monitoring the rainfall and calling the Texas Medical Center and Bedient frequently with updates.

As the morning progressed, the Rice/TMC Flood Alert System was elevated from a green to a yellow to an orange warning level, but the rain stopped about one inch short of sending Brays Bayou to its banks. After receiving 9.1 inches of rain in the Brays and Main Street area, Brays crested at 25,500 cubic feet per second (cfs) around 10 a.m. At about 28-29,000 cfs, Brays Bayou overflows its banks.

The system allowed Rice administrators to close the university when access became difficult due to high water in Rice Village and along University Boulevard. Rice researchers were also in constant contact with Texas Medical Center officials, and due to the close monitoring the medical center was able to remain open.

“We hope to expand the system to use it on other bayous in the city, allowing us to give more notice for more flood-prone areas of Houston,” Bedient said. “The technology is there to at least give an hour or two notice that water is coming.”

People also needed warning on the Katy Freeway, which became completely flooded in certain areas, stranding motorists, and along Buffalo Bayou and White Oak Bayou, where as much as 14 inches of rain caused massive flooding and damage to homes and cars.

As a next step, Bedient would like to get the Harris County Office of Emergency Management team more involved in the process at the bayou level where flooding really occurs, and in making the predictions based on an expanded NEXRAD radar system for the city and county.

Bedient and Holder are currently analyzing the Sept. 11 rainfall that fell on Buffalo and White Oak bayous to re-create the situation and, they hope, for use in developing prediction systems for those bayous as well.

“Shutting down the city is expensive,” Bedient said. “It costs $100,000 every time we lose a Metro bus. A flood alert system for the entire city could be developed for the cost of the four buses Metro lost during Frances.”

According to the recent National Wildlife Federation report, “Higher Ground,” Houston/Harris County is near the top of the list for areas with repetitive flood disaster claims with the Federation Emergency Management Agency (FEMA).