Reducing floodplain development doesn’t need to be complex, say researchers

A paper, titled “How local governments avoid floodplain development through consistent implementation of routine municipal ordinances, plans, and programs,” published in Oxford Open Climate Change uncovers evidence suggesting that, contrary to expectations, most U.S. cities are not doing too badly in avoiding development in areas prone to flooding, and those that are effective appear to be applying existing tools and strategies well, rather than doing anything particularly novel.

Despite billions of dollars of investments and widespread mitigation efforts, the costs of disasters in the United States have grown dramatically. Floods are the most prevalent and expensive U.S. disaster, and while climate change plays a role, the primary reason for rising costs is the concentration of people, infrastructure, and economic activities in hazardous areas.

A 2018 analysis by Climate Central and Zillow found that eight US coastal states are building faster on flood-prone lands than elsewhere.

One of the most effective ways to limit flood damage is to avoid building new infrastructure and housing in flood-prone areas, yet there is little empirical evidence of how effective local governments are at limiting development there and how such governments might improve their efforts.

Numerous studies have researched the contextual factors that lead local jurisdictions to adopt more numerous, advanced, or better-quality floodplain management actions. However, whether more numerous, advanced, and higher-quality actions lead to less floodplain development is less established because few studies have assessed floodplain development outcomes directly.

In this study, researchers reviewed patterns of municipal floodplain development and management in New Jersey from 2001 to 2019. The investigators picked New Jersey because it represents an extreme case. Climate Central and Zillow found that housing growth in the New Jersey coastal risk zone was 3.4 times higher than in surrounding areas.

Five New Jersey cities made the top 10 list for zone risk development, and Ocean City, NJ, built more flood-exposed houses than any other city in the country.

First, the study examined the relationship between wealth and proximity to the coast in development projects. Second, the researchers analyzed how floodplain development relates to municipal capacity and management actions in 128 municipalities across four counties. Finally, they conducted in-depth case studies in four New Jersey towns: Lumberton, Aberdeen, Weehawken, and Woodbridge.

The investigation indicates that most New Jersey cities limit floodplain development more than prior research would suggest given their geographic and socioeconomic context. Between 2001 and 2019, 422 New Jersey municipalities (85% of them) limited the development of new housing in floodplains more than would be expected based on the extent of the floodplain within the municipality and rates of new housing construction.

Some 335 municipalities (68%) limited increases in impervious surface (such as pavement and concrete) in the floodplain. A full 126 New Jersey towns (25% of them) put none of their new housing in the floodplain between 2001 and 2019. Just 14% of New Jersey towns are building in their floodplains more than would be expected based on the size of their floodplains and rate of development.

In interviews with people from the New Jersey towns, practitioners repeatedly stressed practical, common sense behavior, rather than complicated new plans.

“They’re not doing anything special,” one person interviewed during this research explained. It appears most towns can limit floodplain development with a few conventional local ordinances and typical levels of government capacity—not radical innovations or Herculean efforts.

The keys seem to be having a few high-quality land use tools and consistently implementing them, which requires coordination and commitment by local officials.

The paper shows that limited floodplain development is the norm, not the exception, in New Jersey. Municipalities routinely limit floodplain development using land use management and hazard mitigation tools that have been in use for decades and do so with modest and existing levels of local government capacity.

There are multiple paths to limit floodplain development, rather than one best practice, and having a few strong floodplain management tools and focusing on the quality of the social infrastructure (collaboration, commitment, consistency) may be more important than having many tools and trying to implement complicated new plans.

“It’s surprisingly good news,” said A.R. Siders, the study’s lead author.

“There’s room for improvement. But most towns are already taking action. The challenge is how to help them do even more and how to motivate and support the small minority of towns that are still concentrating on new buildings in their floodplains. That’s a very different challenge.”