Overview
As owners start to become more cognizant of the effects flooding, they need to be able to turn to engineering design professionals that can make them aware of the resources available to help protect their assets and help implement cost-effective change.
Keith Gaynor delves into the differences between active and passive flood protection measures.
Flooding causes an average of $8 billion in damage each year across the U.S. and Houston, TX is no exception (NOAA). Within the last few years, residents in the Houston area have experienced unprecedented flood events — Memorial Day (May 2015), Tax Day (April 2016), and Hurricane Harvey (August 2017) — which wreaked havoc on many commercial property owners and campuses. These floods inundated their first floor and basement level spaces as well as on-grade and underground parking garages, rendering these structures unusable for many months and costing owners millions of dollars in flood damage repairs. Many of these owners have since turned to engineering professionals to assist them in retrofitting their properties to protect against flooding.
As owners start to become more cognizant of the effects flooding, they need to be able to turn to engineering design professionals that can make them aware of the resources available to help protect their assets and help implement cost-effective change.
Structural flood protection measures can usually be classified into two general categories: active and passive. According to the Federal Emergency Management Agency (FEMA), active measures are defined as systems that require human intervention or power to operate correctly and need sufficient warning time to mobilize the necessary labor and equipment in order to implement. Types of active measures can include swing and drop-in flood gates, submarine flood doors, stackable flood logs, and inflatables or sand bags.
Passive measures do not require any human intervention and because of this can be thought of as 24/7 flood protection. These types of measures can include structural flood walls, landscape berms, levees, and “float-up” flood gates. Float-up flood gates work great at the tops of loading docks and in front of building entrances where access is required. Walls help keep floodwaters off the site, but also don’t allow for rain falling within the site to drain out. Pumps need to be sized correctly to direct rainwater off-site and backflow prevention needs to be provided in cases where floodwaters may back up through an underground system.
Murphy’s Law states, “Anything that can go wrong, will go wrong.” This is usually the case during flooding events. Electrical power is typically lost, building personnel are often unable to get onsite due to rising floodwaters, or are simply unfamiliar with the flood emergency plan that has been put in place for the site. If any one of the aforementioned items occur, active flood measures are prone to, and usually do, fail. Passive measures are a preferred course of action when protecting critical assets against flooding events. It should be understood, however, that passive measures cannot always be implemented when retrofitting a site for flood mitigation. This may be due to site constraints, lack of structural support systems, or even lack of capital funding.
Floodwaters will always take the path of least resistance. That is why no stone should go unturned when evaluating a site for flood protection. As owners start to become more cognizant of the effects flooding has on their long-term investments, they need to be able to turn to engineering design professionals that can not only make them aware of the resources available to help protect their assets, but help implement cost-effective change as well.
This text was originally published in Walter P Moore’s 2018 Stewardship Report.
