100-Year Flood? Shoot, Houston Is in Trouble During a 10-Year Storm

Close-up of a Harris County ten-year flood zone map. (Brace yourself, Meyerland. Again.)
Close-up of a Harris County ten-year flood zone map. (Brace yourself, Meyerland. Again.)

The Houston Press has acquired a map depicting Harris County’s ten-year flood zones, and the document shows that Brays Bayou, despite multimillion-dollar improvements, can’t even protect against a relatively ho-hum downpour.

Much like what occurred during the Memorial Day floods, the map shows flooding immediately to the north and south of Brays Bayou, affecting properties on South Braeswood Boulevard, Braesheather Drive and South Rice Avenue. However, Harris County officials and hydrologists classified the May 25 and 26 rains as a 100-year storm, not a ten-year rain.  

The map, provided by a source who wished to remain anonymous, was procured from the HCFCD offices, says the source.

As of last September, the Harris County Flood Control District and the United States Army Corps of Engineers had spent $305 million on widening and improving the 21-mile watershed. But no work has been done on the section of the bayou between Chimney Rock Road and Loop 610 – where Meyerland sits – and the $480 million project between the HCFCD and the Corps of Engineers is at least eight years behind schedule.

The Press contacted Harris County Flood Control District executive director Mike Talbott, who wouldn’t respond directly to the Press. We submitted written questions to HCFCD spokeswoman Kim Jackson, who emailed us these prepared responses from Talbott: 

Much of the Meyerland area is located in the 100-year floodplain, and there are homes/structures in the Meyerland area that are in the 10 percent, or 10-year, floodplain. If the area experiences a 10-year storm, there is a chance that those homes will flood from Brays Bayou going out of banks.

In general, some of the Meyerland community is located at relatively low elevations compared to the banks of Brays Bayou and these are among the first to fill with stormwater when the bayou overtops its banks in that area. During major storms, such as the storm that occurred on Memorial Day 2015, Meyerland and other communities also had stormwater from street drainage systems backing up into streets and some homes.

Project Brays’ stormwater detention basins have had a positive effect on reducing downstream communities’ flood risks. The basins hold stormwater during periods of heavy rainfall and slowly release the water back into the bayou as the bayou recedes. As sections of the basins have been completed, they are able to hold more and more water – water that would rush downstream if the basins were not there. For example, though many Meyerland homes were affected by floodwater during the Memorial Day 2015 storm, additional homes would have been affected if the basins were not in place.

When asked why the HCFCD and Corps of Engineers completed work at and near the Texas Medical Center and then jumped upstream to build a retention basin near Highway 6 – and if additional flood risks have been shifted to the Meyerland area and other downstream communities – Talbott offered the following:

As with all flood damage/risk reduction projects, work must be carried out in a particular sequence in order to avoiding impacting (flooding) communities in a downstream or upstream location.

For channel work, you must generally start work at the downstream end of a bayou or creek because you are widening and deepening the channel to move (convey) more flood water. If you widen and deepen upstream, then you create a situation where there is a potential to move the flooding to another area that is not ready to receive the flood water. The “conveyance” portion of Project Brays is designed to move more stormwater, so the Harris County Flood Control District started work on Brays Bayou at the Houston Ship Channel (downstream) and work has steadily progressed upstream in segments to Lidstone Street and from Calhoun to Bertner.

We are currently building the section of Brays between Lidstone and Calhoun Road. The next segment to go under construction will be from Bertner to Buffalo Speedway; and following that is the segment from Buffalo Speedway to South Rice Boulevard, which is the section of Brays near the Meyerland community. This has always been our planned approach to Project Brays. We have not abandoned the project section near Meyerland to jump upstream and build detention near State Highway 6. The channel work we have completed so far has not increased (or yet decreased) risk in the Meyerland area… in no way have the basins upstream shifted risk to the Meyerland area; and in fact, the area would have had higher levels of floodwater if the basins had not been in place.

Work has not stopped on the Brays Bayou Flood Damage Reduction Project ("Project Brays") since the project's inception. The work has proceeded continuously on separate elements, including stormwater detention basins, channel widening and deepening segments, and bridge reconstruction or modifications. There have been periods when the number of elements – or "projects" – under construction was limited due to available funding and other constraints, such as delays caused by utility relocations, property acquisition, etc. 

One thing Talbott wouldn't tell us: If Meyerland floods during a ten-year rain, what happens during a five-year storm?


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