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WEB-BASED HANDBOOK (Legacy Edition). CLICK HERE to submit comments.
Because of staff changes and Randolph Langenbach's retirement from FEMA, these handbooks were never published on the FEMA website.  These are the only copies available.


 

Chapter 4: BUILDINGS

A. Floodwater Inundation

Introduction

Problem:

Damage to buildings, equipment, and other components are most commonly caused by floodwater inundation. Floodwater inundates the building, saturating the building materials and its contents. The floodwater is usually contaminated by a number of substances, such as sewage and other hazardous materials.

Mitigation Objective:

The most effective mitigation is fully protecting the building facility from floodwaters, such as through relocating or elevating the building.

A.1 Relocate Building

Relocate the entire building out of the area subject to flooding and to a safe area, outside the 100-year floodplain or a 500-year floodplain if a critical facility.

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Effectiveness:

  • The most effective mitigation possible, as the structure will no longer be subject to flooding.

Limitations:

  • Appropriate receiving site must be obtained

Considerations:

A.2 Elevate Building

Elevate the building facility on fill or a structure above the design flood elevation or above the 100-year flood. Buildings can be elevated on perimeter walls, piers, piles, or fill. If walls are used to elevate, they must be vented to accommodate hydrostatic forces.

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Effectiveness:

  • Very effective
  • Area under the building (if built on piers) may be used for storage, parking, or access.

Limitations:

  • Building access will be impeded during flood events.
  • Fill should be compacted and protected from erosion.
  • May require additional mitigation considerations for areas of heavy debris loading.

Considerations: 

A.3 Wet Flood-Proof Building

Allow floodwater to inundate selected portions of the facility in areas that are not vulnerable to damage from floodwater saturation by using water-resistant construction methods, designing openings for flood water passage, and elevating vulnerable systems, such as electrical equipment above the design flood elevation. Design should include the construction of openings to equalize hydrostatic pressure, and construction of the walls to resist hydrostatic pressure.

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Effectiveness:

  • Very effective

Limitations:

  • Portions of building vulnerable to floodwater will be inaccessible during flood event.
  • Not practical in areas of high velocity or debris impact.
  • Advance warning needed so that stored materials can be removed

Considerations:

A.4 Dry Flood-Proof Building

Seal the building so that floodwater does not enter. Components of dry flood proofing may include: 1) Constructing exterior floodwalls; 2) Constructing an impermeable berm around the facility; and/or 3) Sealing the building with water-proof material.

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The buoyancy of the building must be considered.  Hydrostatic and hydrodynamic forces must be taken into account.

effectiveness:

  • Very effective in preventing damage to building contents.
  • Berms and floodwalls can be integrated into landscaping.

Limitations:

  • May not be practical in areas of high velocity flows or heavy debris loading.
  • May require access gates be maintained and closed prior to floodwaters reaching structure
  • Site should be designed to resist the forces of floodwaters and accommodate on-site drainage needs.
  • Slopes exposed to moderate or high velocity flows should be armored

Considerations:  

A.5 Install Backflow Devices on Sewer Drains

Install backflow devices, including one-way and ordinary valves, on sewer lines and floor drains. These devices prevent sewage and/or storm water from being forced back into the facility.

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effectiveness:

  • Very effective, particularly for buildings outside of the floodplain.

Limitations:

  • One-way valves may become blocked by debris and fail to close
  • Gate valves require that the valve be manually closed prior to inundation.

Considerations:

 

 

NOTE:  None of the mitigation measures in these Handbooks should be considered ‘pre-approved’ or otherwise automatically eligible for FEMA funding. Only FEMA staff can determine eligibility, once they have determined that an applicant is eligible and they have reviewed a project proposal.

FEMA HAZARD MITIGATION HANDBOOKS                                                                        Updated: June 13, 2002