Detention Requirement Solutions

Hurricane Harvey

Hurricane Harvey made landfall in Texas on Aug. 25, 2017, as a Category 4 hurricane. After making landfall three times in six days, this horrific storm caused roughly $125 billion in damage. An estimated 13 million people were affected and nearly 135,000 homes were damaged in the historic flooding. Hurricane Harvey prompted both City and County officials to make changes to the regulations that govern development in this rapidly growing area.

City and County Flood Control Regulations

Since the mid-1980s, it has been the adopted policy of both the City of Houston and Harris County that new developments should mitigate their own impacts on flooding. The policy was that new development should not be allowed to increase flooding upstream or downstream or create any adverse impacts. The most often used tool for mitigating development impacts is detention. Detention ponds collect and hold stormwater runoff from streets and buildings and release it slowly, reducing the rate of flow downstream. Following Hurricane Harvey, stricter regulations were implemented to prevent the sustained damage caused by hurricanes and other natural disasters.

Stricter Regulations Post Harvey

Construction is currently underway on a new Marriott Fairfield Hotel in Houston’s Energy Corridor area.  To meet the new drainage requirements, this project has an underground detention vault which satisfies the City of Houston’s increased detention pond requirement.

Texas Department of Transportation (TxDOT) regulations have to be followed for the segment that drains to TxDOT and City of Houston regulations for the remaining mitigation. Both agencies require Atlas 14 rainfall intensities which are roughly 20% higher than before. This will result in larger pipes and larger detention. Since Harvey, the City of Houston has changed the minimum detention requirements and will not give credit for existing impervious area. Detention is based on development area and the minimum finish floor elevation.

The civil division of Huitt-Zollars designed the detention vault at Marriott Fairfield using a concrete slab, concrete perimeter walls, and load bearing CMU divider walls which creates chambers within the vault. Each of the divider walls are constructed with pass-through openings to equalize the water level allowing all chambers to reach the outfall. Hollow core precast concrete planks will lay on top of the vault, supported by the concrete and CMU walls. Paving will then be poured over the top of the vault, locking all the components together. Maintenance and inspections are key to the functionality of the detention vault. This will be achieved through two manholes cast into the concrete paving with access ladders. The detention volume has a volume of 77,292 cubic feet and measures 8,223 square feet at a depth of 9.40 feet.

Creative detention and mitigation are key elements to the success of new developments. This will continue to be highly debated as more strenuous rules and regulations emerge.