FEMA on passive floodproofing

FEMA issued a new Floodproofing Non-Residential Buildings publication  (FEMA P-936 ) to assist local government officials, engineers, architects, and property owners involved in the planning and implementation of floodproofing retrofits. It reflects the latest information on floodproofing retrofits for non-residential structures, and provides guidance on floodproofing existing non-residential buildings in riverine areas subject to shallow flooding and coastal areas not subject to wave action.

This FEMA publication focuses primarily on dry floodproofing, which is making a structure watertight below the expected flood level but provides an overview of other retrofit methods that can be used in conjunction with or independent of dry floodproofing, including: wet floodproofing, floodwalls, levees, protection of utilities and emergency floodproofing measures.

FEMA recommends floodproofing with passive measures whenever possible.

FEMA recommends passive floodproofing whenever possible(Sec 1.2 Definitions and Key Concepts)

 Passive floodproofed buildings result in lower NFIP insurance premiums

Dry floodproofed buildings with active floodproofing measures and requiring human intervention are subject to higher insurance premiums than dry floodproofed buildings with completely passive floodproofing measures that do not require human intervention.        (Sec 2.1.1 National Flood Insurance Program)

Flood Emergency Operations Plans: Higher risk with active measures

  • If the proposed floodproofing measure is active (requires human intervention), all roads that provide access to the building should remain passable long enough for the floodproofing measures to be installed and for all personnel to safely evacuate the site.
  • When removable shields (i.e. drop in panels, flood panels) are used, flood emergency plans must include: storage location, method of installation, maintenance of equipment, annual installation practice.
  • Regular evaluation and update of the flood emergency operations plan must be scheduled to reflect changes in personnel and procedures.                                            
    (Sec 2.5.4 Flood Emergency Operations Plan)
Adequate flood warning time is essential 
Flash flooding happens quickly and comes unexpectedly.  Without sufficient warning time, active measures cannot be implemented putting people and property at risk.
Texas Medical Center hospitals weren't able to deploy active flood barriers before the flash flooding overwhelmed their flood control system

“The water came so fast it was impossible to secure all of the logs,” Garcia said. “As soon as we secured the first log, the water began to rise above it. We tried a second, then a third. By the time we got to the fourth log the water was above my thighs. I knew it was time to head for safety.”    FEMA Case Study

Other related reference publications: