Policy Documents

Flood Risk Perception in Lands “Protected” by 100-year Levees

Jessica Ludy and G. Matt Kondolf –
August 2, 2011

Under the US National Flood Insurance Program, lands behind levees certifiedas protecting against the 100-year flood are considered to be out of the officially recognized‘‘floodplain.’’ However, such lands are still vulnerable to flooding that exceeds the designcapacity of the levees—known as residual risk. In the Sacramento-San Joaquin Delta ofCalifornia, we encounter the curious situation that lands below sea level are considered not‘‘floodplain’’ and open to residential and commercial development because they are‘‘protected’’ by levees. Residents are not informed that they are at risk from floods, becauseofficially they are not in the floodplain. We surveyed residents of a recently constructedsubdivision in Stockton, California, to assess their awareness of their risk of flooding.Median household income in the development was $80,000, 70% of respondents had a4-year university degree or higher, and the development was ethnically mixed. Despite thelevels of education and income, they did not understand the risk of being flooded. Giventhat literature shows informed individuals are more likely to take preventative measuresthan uninformed individuals, our results have important implications for flood policy.Climate-change-induced sea-level rise exacerbates the problems posed by increasingurbanization and aging infrastructure, increasing the threat of catastrophic flooding in theCalifornia Delta and in flood-prone areas worldwide.