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American Society of Landscape Architects


May 2008 Issue

Decreasing the Cost of Flooding
Accurate flood maps can save property and lives in landscape architect-designed projects.

By James L. Sipes, ASLA, and Kimberly A. Sipes

Decreasing the Cost of Flooding C/O FEMA And Denver Urban Drainage and Flood Control District

Floods inflict more damage and economic losses on the United States than any other natural disaster. Perhaps one reason is that more than 30 million Americans live in areas that have a high risk of flooding. 

During the 10 years from October 1992 through October 2001, flooding caused more than 900 deaths and resulted in approximately $55 billion in damages. The greatest loss was in 2005, when loss payments totaled $17.4 billion, in large part because of flooding caused by hurricanes Katrina, Rita, and Wilma.

Limitations with Flood Mapping

Why is flooding such a big problem? One reason is that Federal Emergency Management Agency (FEMA) flood maps, which are intended to define areas that are “safe” from flooding, are outdated and inaccurate. Flood maps have been produced and used for 35 years, and many have not been updated in years. According to FEMA, nearly 70 percent of the nation’s approximately 92,222 flood maps are more than 10 years old, and many of these maps no longer accurately reflect current flood hazard risks. As a result, development is occurring in areas that should be restricted because of flooding hazards. FEMA made an effort to transfer its paper maps to digital format in the 1990s, creating what’s known as the Q3 flood data. This Q3 data has been the foundation for many design and planning decisions over the years. But landscape architects using Q3 flood data are using outdated information.

To be blunt, there are many problems associated with Q3 flood data. The horizontal control of Q3 flood data is consistent with that used for 1:24000 scale maps, which is acceptable for community and regional scale planning projects but is not useful for site-scale projects.

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