Flood-Proofing Strategies

Even before Hurricanes Katrina and Rita devastated the Gulf Coast, The Methodist Hospital (TMH), situated in a low-lying area of Houston, had begun protecting itself against flooding with a new $1-million flood-proofing system.

Begun in 2002 and completed before Katrina hit in '06, the

system extended over the entire medical campus. "We made sure we weren't going to have a repeat of Hurricane Allison," said Doug Rand, TMH director of engineering. That hurricane, in 2001, did $400 million worth of damage to the hospital and essentially shut it down for more than a day. Floodwaters flowing downhill from the landward north side put the entire campus under a foot of water, dumping up to 28 feet into some underground garages and tunnels joining the buildings.

Hurricanes aside, frequent flash flooding is a familiar bane to Houstonians. It's worse around TMA, just five blocks away from Brays Bayou, leading to the Gulf of Mexico. Because of its labyrinthine substructure, mere inches of surface water become several feet down in those basements.

Two Threat Scenarios

Working with Charlie Penland of the engineering firm Walter P. Moore and Associates (WPM) and Hoagy Cannon of Vaughn Construction, hospital engineers developed flood-proofing strategies against two likely scenarios:

• Flooding from the north, which is the more frequent, builds up fast and can overwhelm the drainage system; and

• Flooding from the south, which is potentially higher and more damaging.

"Entrances to underground garages beneath buildings were the biggest problems," said Penland. "Their wide openings can let in a lot of water fast." So WPM designed a low floodwall, attractive but functional, to surround the entire campus and specified huge Presray flood-proofing gates for the entrances to all garages and down-ramps to loading docks. Equipped with dual inflatable seals on the bottom and sides, the massive gates swing or slide into place. Then the seals are inflated using compressed air tanks built into the doors. Their job is to prevent most of the water from getting into the buildings in the first place.

As the next line of defense, underground tunnels up to 28 feet below grade are protected with swinging flood doors that close off the tunnels completely. Their inflatable seals run around the entire periphery and can withstand up to 50 feet of head pressure. When not in use, the doors swing out of the way and blend in with the interior finish.

A neighboring hospital, Texas Children's Hospital (TCH), had the same Presray side-hinged doors already in place before Hurricane Allison. Although 5 feet of water accumulated outside one of the tunnels, not a single drop got in. As a result, TCH has remained fully operational during numerous floods, even taking in patients that other hospitals had to turn away.

"Their experience certainly motivated us to act, and gave us the confidence that we could actually keep floodwaters out," said Rand.

Additional Safeguards

The TMH flood-proofing plan also included two additional safeguards:

• Checking valves in sumps and storm drains to prevent backflow; and

• Strengthening and sealing the first two or three feet of the entire structure to prevent seepage.

"Barriers in the openings, though key, are only part of a truly functional flood-proofing system," Cannon advised. The team also established a responder training program with mandatory proficiency exercises to be sure every single barrier does its job when needed, and that employees can deploy them in three minutes. These are to comply with FEMA standards for in-place flood-proofing of existing buildings and to qualify for insurance under the National Flood Insurance Program (NFIP). New FEMA/NFIP standards require hospitals to be flood-proof to 500-year flood standards. The team set the flood protection height 1.5 feet above FEMA standards to account for wind and wave action and qualify for lower flood insurance rates.

Key Appearance Issue

The most challenging aspect of the TMH project was to flood-proof one small, private parking garage, which had a very appearance-sensitive exterior wall. This was where Dr. Michael deBakey, the cardiology pioneer, parked beneath the building where he worked. The polished granite entry wall holds numerous commemorative plaques about his achievements, plus donor rolls. This was no place to hang a no-nonsense floodgate that looked like a piece of a battleship.

Penland and Rand worked with Presray engineers to develop a massive sliding gate — like a pocket door — that hides in a recess when not in use, yet can be deployed in minutes. It measures 10 feet by 30 feet and weighs three tons, yet two people can slide it into place in minutes. In normal times, one would never know it was there.

Numerous single-width employee doors are also protected with Presray swinging, sliding or lift-out panels to complete the flood defense system. Vaughn Construction of Houston handled the installation under Presray's supervision, so the whole job came in on schedule.

Now one month into the 2006 hurricane season and already pounded by flooding, TMH's Doug Rand remarks, "We're ready."