3000 Post Oak Flood Protection

Disaster Averted: Flood Gate Design Weathers Three Major Storms

Houston, Texas has long been known as the Bayou City, although in recent years has earned a reputation as the Flood City. Even areas not located within the 100-year flood plain have experienced flooding conditions during two recent events — the Memorial Day Flood of 2015 and the Tax Day Flood of 2016.

Such was the case for 3000 Post Oak, a 19-story commercial office building that houses the oil, gas & chemical global operations of a worldwide engineering firm. The infamous 2015 Memorial Day Flood was heavily concentrated over southwest Houston, and within six hours had dropped 11 inches on grounds already saturated from the previous two months’ heavy rains. As the streets adjacent to 3000 Post Oak exceeded their capacity, the deluge flooded the tower’s basement via the below-grade loading dock, with waters reaching 9.5 feet.

Unfortunately, all of the building’s critical mechanical systems were located in the basement, and given the structure’s age, typical remediation efforts such as relocating these systems to upper levels was simply not feasible. It took seven days to restore operations to 3000 Post Oak, which also meant seven days of downtime for hundreds of employees at one of Bechtel’s major global offices.

Walter P Moore’s Civil and Diagnostics groups were asked to conduct a site analysis and to fast-track a design that would protect the tower from future flooding. The combination of a below-grade loading dock that essentially invited water in and basement-level critical spaces that could not be relocated proved exceptionally challenging in determining the most resilient solution. We surveyed the building to identify areas most vulnerable to water infiltration and conducted a runoff analysis to determine how much water would enter the site from overland flow, storm sewers, roof drainage, and from the face of the building.

Based on the survey results, we recommended a hybrid solution of active and passive flood protection systems. In general, an active system requires a person to physically activate it, whereas a passive system is activated by flood waters and therefore, is more automatic. Although passive measures typically have a higher capital cost up front, our client requested passive systems where feasible to alleviate the responsibility on employees. Because weather conditions, and especially flash floods, can change so rapidly, there is often not enough time to get to the facility to activate protective systems.

The final solution was to install a flood gate at the top of the loading dock (passive) and flood doors at the entrances to the basement at the loading dock (active). The flood gate is 30 inches high (determined by historical water heights) and deploys automatically as the water rises. Earth berms (passive) were also created as natural means of redirecting flow and aiding absorption to lessen the load on the structure.

Before the flood protection measures were 100% complete, the monumental Tax Day Flood of 2016 hit, dropping 16 inches of rain in less than 12 hours. Fortunately, the flood gate had been finished five days earlier, with testing scheduled to be performed the following weekend. Instead, it was the Tax Day storm that provided the testing, but the building easily weathered the storm, suffering no damage.

In September 2017, Hurricane Harvey set records in every category unloading 33 trillion gallons of rain, devastating many areas along Texas' Gulf Coast. In Harris County alone, 1 trillion gallons of water fell over the course of four days shutting down businesses, flooding neighborhoods, and displacing thousands of families. Because many roads were closed due to flash flooding, the automatic response of the gate was imperative as it would have been dangerous for the property manager to have to navigate their way to the building to manually activate the flood gate. While many property managers nervously watched the waters invade downtown Houston and the Galleria, the 3000 Post Oak property remain unaffected by the increasing flood waters.