City engineer’s report tonight: Bellaire needs help to stop flooding disasters

October 2, 2017

By Charlotte Aguilar

Bellaire’s tightened homebuilding regulations are working, its infrastructure plans should help — but ultimately the city can’t protect homes and residents against catastrophic flooding without regional solutions.

That’s the conclusion of a report by Bellaire’s veteran consulting City Engineer James Andrews that will be delivered to City Council tonight (Monday, Oct. 2). The session kicks off at 6 p.m. in Council Chambers at City Hall, 7008 S. Rice Ave., starting with a public hearing on increasing the property tax rate (details here).

The report places the number of Bellaire homes with actual flooding in living spaces from Hurricane Harvey at 1,936 out of 6,688 — 2,318, when garages and other structures are counted. That’s compared with Bellaire’s previously worst weather disaster, when Tropical Storm Allison flooded 1,432 homes in June 2001.

Arguably the best news in the report is that of homes built since tighter controls started being put into effect in 2005, in response to Allison, only 6 percent — 47 homes — took in water. Those standards “provided greater protection during this catastrophic event,” says the report.

Bellaire’s homebuilding regulations limit the amount of fill on residential lots, mandate that new construction be built one foot above the 100-year floodplain, and require an elevated, open foundation that allows water to be absorbed in a permeable surface under homes and to flow through once the ground is saturated.

Andrews’ report describes Bellaire’s challenging factors — rainfall of about 50 inches per year and a growing number of catastrophic “events,” poorly absorbing clay soil, the proximity to an “undersized” Brays Bayou, and flat topography with poor water flow.

The city suffers from what he described as shallow floodplain flooding, worst in the southeast corner of the city when the bayou overflows its banks, and from ponding that occurs throughout the city during prolonged, heavy downpours when rainfall exceeds storm sewer capacity.

Harvey, the report concludes, was an “extreme combination of both types of flooding events.”

Bellaire’s plans to increase underground detention from a two-year to a 100-year storm level capacity — part of the 2016 Bonds for Better Bellaire program — and installing backflow devices to keep bayou water from entering the underground box culverts should also help alleviate flooding, according to the report.

To even begin to manage what is described as “absolutely devastating amounts of rain…2,500-6,000 year levels,” as in Harvey, Andrews will say that bayou capacity will need to be increased by Project Brays.

“There is nothing the city of Bellaire can build on its own to remove flooding conditions during an event of this magnitude,” the report concludes.

The city engineer’s report on Bellaire flooding shows 1,936 homes took in water during Harvey — most of them constructed before stricter building standards were adopted in 2005. (Photo by Charlotte Aguilar)

 

 

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