PERMANENT FLOOD BARRIERS: LEVEES AND FLOODWALLS
INSIDE THE FLOODPLAIN

What Is It?

Cost: Varies by height above ground.
Levees/berms:
-2 feet: $60/linear foot
-4 feet: $106/linear foot
-6 feet: $170/linear foot
Floodwalls
-2 feet: $92/linear foot
-4 feet: $140/linear foot
-6 feet: $195/linear foot
Applications: Levees are most practical for new construction as they require excavation and a large amount of space. Floodwalls can be more easily retrofitted to existing sites.
Service Life: Extensive (up to 50 years). Regular maintenance required.

Vulnerable building sites can be protected from floods through the use of levees and floodwalls. Levees and berms are structures made of compacted earthen materials with interior cores of impermeable soil (i.e. clay). Construction typically begins with excavation to ensure subsurface soil conditions are taken into account in design. Floodwalls are typically engineered structures made of reinforced concrete. Floodwalls can be built up to 20 feet in height and can be designed to be aesthetically pleasing architectural and landscape features. Floodwalls are typically more expensive to construct than levees, but require less space and landscaping and are more resistant to erosion. Construction of all floodwalls and levees should be undertaken by licensed engineers.

Due to the large amount of space needed for construction, the use of levees andfloodwalls may be difficult and cost prohibitive in urban environments and may only be suitable for integration into new construction. In particular, levees and berms require a large quantity of earthen fill, and a lack of readily available, nearby fill may cause transportation costs to be prohibitive. Higher levees and floodwalls require significantly more support to withstand the greater water pressure exerted on the barrier. Strengthening levees and floodwalls requires increases in size, which may exceed the amount of space available on a building site and become impractical. Levees are typically limited to 6 feet in height and floodwalls to 4 feet to maintain cost-effectiveness. Sites with expected flood depths that exceed practical barrier heights should consider using alternate methods (e.g. elevation or floodproofing) instead of or in addition to permanent flood barriers. Barriers must be located a sufficient distance away from structures with basements to prevent damage to basement walls from the additional pressure from saturated soils. Regular maintenance is crucial to maintain service life.

Benefits

  • Floodwalls and levees will protect a building site from floodwater damage. As a result, protected structures will not need additional modifications for flood protection.
  • Site aesthetics can be preserved or enhanced. Floodwalls can utilize decorated bricks or be built into garden areas.

Drawbacks

  • Levees and floodwalls cannot be used alone to bring substantially damaged or substantially improved structures into compliance with floodplain management ordinances and laws.
  • The amount of excavation and space required for levees may make them impractical for existing sites and most building sites in urban areas. Floodwalls may be applicable in these sites, but are more expensive to construct.
  • The use of levees and in some cases floodwalls may affect drainage in the area, potentially worsening flood damage in adjacent sites.

Regulatory Impacts and Requirements

A summary of regulatory touchpoints follows below:
Levees-and-Floodwalls

Financing Options, Incentives, And Rebates

Additional Resources

PROJECT EXAMPLES

  • Lourdes Hospital, NY: 11 FloodBreak passive floodgates combined with 11-foot floodwall at a cost of approx. $7 million
  • New Orleans, LA: After the infamous design failure of the levee and floodwall system in 2005 during Hurricane Katrina, a $14.5 billion civil works design
  • Haverhill Floodwall, MA: $5.4 million in repairs to a 30 feet floodwall along the Merrimack River.

SAMPLE OF SUPPLIERS

  • Building/landscaping contractors

SOURCES

Photo credit: CC BY 2.5 (http://creativecommons.org/licenses/by/2.5)], via Wikimedia Commons