Research & Commentary: Flood Mitigation, Levees, and Flood Maps

Published December 21, 2010

Flood insurance maps inform owners of property on U.S. coastlines and riverbanks of flood damage risks their properties might face. The Federal Emergency Management Agency (FEMA) is primarily responsible for drafting these maps, which are in the midst of a massive modernization effort.

The maps contain several different risk gradations, and “high-risk” designations have a major effect on the homeowners living there. Homeowners with federally backed mortgages (securitized by government-controlled Fannie Mae and Freddie Mac) are required to purchase flood insurance after a downgrade of status, even if the area has no previous history of flood damage. Wholly private mortgage securitizers generally follow suit.

Two things—changes to maps and changes to levees—can result in areas being designated high-risk. In general, risk is determined based on hydrological calculations rather than actual loss experience: When terrain changes (a body of water rises, for example) or, more importantly, when a levee gets decertified. When a levee is decertified (meaning mappers believe it no longer confers 100-year protection, even if it’s otherwise in good condition), the homeowners behind it generally have to purchase insurance.

Levee certification matters because, for more than a century, the United States has attempted to control water almost entirely with levees and other “structural” means. During that time, the cost of flood damage has more than tripled in inflation-adjusted terms. Groups such as, an alliance of environmental advocacy organizations and free-market groups, say flood mitigation policy should focus on moving development away from environmentally sensitive and high-risk flood plains instead of building new levees. Others, particularly organizations and individuals in heavily flood-prone areas that already have many levees, favor the construction of more levees.

Legislation allowing homeowners to delay the purchase of flood insurance in newly reclassified flood zones due to levee decertification has come before Congress. Proponents maintain the delay would allow more time for areas facing insurance rate hikes to repair or upgrade their levees and prepare for the higher flood insurance rates. Opponents say that although the current process could use improvements, a suspension of purchase mandates would make the problem worse.

The following articles examine the role of levees in flood mitigation, the importance of accurate flood mapping, and the effects of maps changes on flood insurance.

Levees: The Double-Edged Sword
This policy paper from the Association of State Floodplain Managers examines the use of levees in current flood mitigation efforts and makes suggestions on how levees should be used, primarily as a last resort, in the future.

Levees: The Good, the Bad, and the Ugliness of Certification
This presentation from the Army Corps of Engineers explains the levee certification process and some of the problems municipalities can face in dealing with it.

The NFIP and Levees: FAQ
This FAQ from FEMA explains the agency’s role in the certification process and the importance of examining levees in determining an area’s flood risk.

Mandatory Flood Insurance Purchase in Remapped Residual Risk Areas Behind Levee
This report from the Congressional Research Service examines mandatory flood insurance purchase requirements in remapped flood-risk areas.

Levees—Taking the Long View
This article from the Risk Institute suggests levees will provide better protection if we change the way we regulate and insure development in the areas protected by them.

Midwest Flooding Disaster: Rethinking Federal Flood Insurance
This report from the Congressional Research Service reexamines federal flood insurance after the 2008 Midwest floods. It includes discussion of levee failure and suggests changes in levee policies may be needed.