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Definition

Wet floodproofing is a method of flood preparation that involves building designs and
wetVSdry.jpg
Figure from 'A Stronger, More Resilient New York'
material choices that allow for the entry of floodwaters into the structure, while minimizing the potential negative impacts and damage caused. This resilience measure should be designed to account for the height of building flood elevations, buoyancy and hydrostatic pressures of flood waters, and wave action. [1]

Wet floodproofing differs from dry floodproofing in that dry floodproofing measure take steps to prevent the entry of water entirely (see figure at right for further comparison).[2]

Wet floodproofing measures:
• Ensure flood waters may both enter and exit the structure
• Ensure flood waters on the interior of the structure rise and fall at the
same rate aa flood waters on the exterior
• Protect structural elements, objects, and materials that are below the DFE
from damage and corrosion caused by contact with flood waters
• Protect mechanical and service equipment located on the interior or exterior of the structure
• Ensure items located in floodable areas below the DFE are secured or moved away from floodable areas [3]


Issues Addressed

Wet floodproofing addresses the need to accommodate increased flood risk, and adapt buildings to become more resilient in flooding events. New York City has experienced flash floods, storm surges, storm tides, river floodings, and inland flooding events caused by extreme weather such hurricanes, tornadoes, nor’easterss and high precipitation events.[4]

New York City’s more than 600 miles of coastline means a large volume of the built environment exists within 10 feet of average sea level. Global sea level rise is a slow, yet steady, process, which incrementally increases the chances for various types of flooding that impact coastal areas. The New York City Panel on Climate Change has stated that “as sea level rises, coastal flooding associated with storms will very likely increase in intensity, frequency, and duration.” Increased precipitation is another projected factor in future climate change models. Volume of annual precipitation may increase by as much as 10% by the 2080’s.[5] These combinations of risk factors are resulting in the adjustment of Federal flood hazard mapping to show increased flood risk assessments that continue to rise throughout the next century.[6]


Extreme weather NYC.jpg

Special Initiative for Rebuilding and Resiliency (SIRR)

Wet floodproofing falls within the scope of SIRR goals for buildings:
  • Strengthen new and rebuilt structure to meet the highest resiliency standards
  • Retrofit as many existing buildings as possible to improve resiliency
Wet floodproofing methods address Iniative 7 of the Buildings chapter “Encourage existing buildings in the 100-year floodplain to adopt flood resiliency measure through an incentive program and targeted requirements”. Dozens of DDC buildings exist within the SIRR flood zones. Public buildings have the opportunity to set precedent and stand as examples for surrounding private structures. Buildings that are retrofitted to adopt wet floodproofing measures should consider the potential to publicize the measures and create signage to demonstrate proper application of the measure to citizens.[7]








Considerations

Wet floodproofing may only be an appropriate resilience method for certain buildings and uses. Acceptable situations include flooded areas that are used for non-residential uses including basements, sub-floor crawlspaces, parking garages, storage areas, and some commercial areas. It is also important to note that wet floodproofing does not guarantee protection from high hydrostatic pressures caused by fast-moving flood water, wave action, and any debris that is carried by those flood waters. Considerations for these types of events may require the use of flood barriers, green infrastructure, shoreline protections, levees, or flood walls to combat effects.

Wet flood proofing measures should be aligned with a building’s Emergency Plan. Some components of wet floodproofing involve actions on the part of building occupants in order to be successful. If pumping of floodwaters is required, it should be noted that risk of structural damage is increased when surrounding foundation earth is saturated. Pumping may need to be done slowly for this reason. Building enclosures should be designed with drainage in made, and provisions must be made to allow water vapor to evaporate to the interior, exterior, or both, in order to avoid mold and structural rot associated with trapped water. Building mechanical systems should ideally be relocated to floors above the DFE. Any equipment that cannot be permanently located above flooding areas should be easily movable and identified as objects that require relocation when flood risk is high.[8]

Sep-Smart-Vent-7.jpgCosts
In a cost comparison of floodproofing methods, it is often the case that wet floodproofing measures are less costly than dry floodproofing measures. This is due to the fact that structural reinforcements, watersealing measures and flood barrier doors are far more costly than flood vents needed to allow waters to flow through. [9]

Flood-Resistant Materials

Building materials that may be categorized as "flood-resistant" must be capable of ensuring the stresses of inundation from freshwater, saltwater, and the debris that is associated with flood waters. Some examples of such materials are:
  • concrete
  • stone
  • masonry block
  • ceramic
  • clay tile
  • pressure-treated lumber
  • naturally decay-resistant lumber
  • metals
These are also materials are generally well-suited to basement and garage settings and are easy to clean once flooding has subsided.[10]

Sep-Smart-Vent-4.jpg
Source: Smart Vent Products, Inc.

Code Compliance

Application of flood vent sizing and location should be in compliance with local permitting and engineering guidelines such as those from FEMA and the American Society of Civil Engineers (ASCE). Similarities between these standards are as follows:

  • Flood vents should be distributed as evenly as possible in order to facilitate the even distribution of water entry and exit. If neighboring buildings or objects prevent even distribution across all wall, it may be possible to two opposite walls, if those vents are designed to accommodate the total flooding volume of floodwaters.
  • The floor, or grade of the lowest interior space must be higher that the surrounding exterior grade. This must be the case in order for water to flow out of the structure, lest flood water becomes trapped in basement areas.
  • Flood vents must be located less than a foot above grade.
  • Flood resistant materials must be utilized in areas that are floodable.
  • To avoid blocking of flood vents by debris, a 3-inch sphere must be capable of passing through flood openings.
  • Flood vents should have screens prevent entry by animals, bugs, and other pests.
  • Windows and air vents cannot serve a dual function as flood vent.
  • Garage doors cannot be assumed to be open at the time of flooding, as power outages associated with extreme weather may have rendered mechanical openers useless.
  • The function of flood vents must be available without any human interaction or preparation.[11]

Applications

FEMA documented a properly applied use of commercial wet floodproofing measures in Key West, Florida at a restaurant located within beach front property at The Duval Beach Club. The restaurant’s owner was interested in reducing the risk of future damage from storm surge and hurricanes after enduring major damage during Hurricanes Rita and Wilma 2005. Owners ensured that appliances and furniture would easily movable so that staff could transport objects to a safe area with short notice. Structural supports were reinforces while some walls were designed to break away with the force of storm surge. Utilities, service paneling, electrical outlets were installed several feet above floor level, out of range of anticipated flooding. Steps were also taken to ensure roof and building structures could endure extreme winds associated with hurricane-strength winds. Further information can be found on the FEMA website.[12]


Related Reports

References


  1. ^ FEMA. Wet Floodproofing | FEMA.gov. Web. 05 Nov. 2013.http://www.fema.gov/floodplain-management/wet-floodproofing
  2. ^











    New York City. A Stronger, More Resilient New York. By Special Initiative for Rebuilding and Resiliency. 2013. PlaNYC http://www.nyc.gov/html/sirr/html/report/report.shtml
  3. ^











    FEMA. Homeowner's Guide to Retrofitting: Six Ways to Protect Your Home From Flooding. 2nd ed. 2009. FEMA P-312. https://www.fema.gov/media-library/assets/documents/480
  4. ^











    "Storm Events Database." National Climatic Data Center (NCDC). NOAA, n.d. Web. 05 Nov. 2013. http://www.ncdc.noaa.gov/stormevents/
  5. ^











    New York Panel on Climate Change. Annals of the New York Academy of Sciences. Volume 1196, Climate Change Adaptation in New York City: Building a Risk Management Response: New York City Panel on Climate Change 2010 Report pages 41–62. May 2010.
  6. ^ AECOM. The Impact of Climate Change and Population Growth on the National Flood Insurance Program through 2100. Tech. 2013. http://www.aecom.com/deployedfiles/Internet/News/Sustainability/FEMA%20Climate%20Change%20Report/Climate_Change_Report_AECOM_2013-06-11.pdf
  7. ^











    New York City. A Stronger, More Resilient New York. By Special Initiative for Rebuilding and Resiliency. 2013. PlaNYC http://www.nyc.gov/html/sirr/html/report/report.shtml
  8. ^











    Extension. "Techniques for Wet Floodproofing." N.p., 24 Sept. 2012. Web. 05 Nov. 2013.http://www.extension.org/pages/13865/techniques-for-wet-floodproofing#.UnRksJQwbEh
  9. ^









    McGraw Hill Construction. Cost Analysis Comparison: Dry vs Wet Floodproofing Technologies. Tech. http://construction.com/CE/articles/2012/Smart_Vent_Cost_Analysis.pdf
  10. ^











    FEMA. Homeowner's Guide to Retrofitting: Six Ways to Protect Your Home From Flooding. 2nd ed. 2009. FEMA P-312. https://www.fema.gov/media-library/assets/documents/480
  11. ^
  12. ^











    FEMA. "Wet Floodproofing Reduces Damage to Popular Beach Restaurant." Lessons Learned Information Sharing. Web. 5 Nov. 2013.https://www.llis.dhs.gov/content/wet-floodproofing-reduces-damage-popular-beach-restaurant