The coastal communities of N.H. have seen their share of recent flood events, including Mother’s Day 2006, Patriots Day 2007 and the March 2010 floods. With increases in land development, impervious surfaces and bigger extreme precipitation events, local towns are experiencing changes in their floodplain areas and are seeking up-to-date data to better prepare for flood events while keeping their risk of litigation low.

To that end, a new report written by faculty and students at the Vermont Law School in collaboration with UNH faculty and staff indicates that towns in the Lamprey River watershed can legally use recently updated 100-year floodplain maps to make land-use decisions.

With funding provided by the National Sea Grant Law Center, the report  “New Floodplain Maps for a Coastal New Hampshire Watershed and Questions of Legal Authority, Measures, and Consequences” provides examples, case studies and a review of judicial precedents to assess towns’ legal risks associated with adopting flood management regulations and policies.

“This legal report will likely be the go-to publication for many communities facing this issue,” said Cameron Wake, UNH research associate professor of climatology and glaciology, who was involved in the maps’ development.

The maps, created by a UNH-led team of researchers and funded by the NOAA/UNH Cooperative Institute for Coastal and Estuarine Environmental Technology (CICEET), are novel from the previous FEMA floodplain maps because they take into account both present-day and future projections of land use and precipitation patterns.

Compared to previous conditions, the updated maps show a significant increase in floodplain area, water surface elevation, and river discharge rates based on a suite of scenarios for land use and climate change projections over the next 90 years, Wake said.

“We’ve already seen significant changes in the Lamprey River basin, which should come as no surprise to people who experienced the major flooding events in 2006, 2007 and 2010,” he added.

During the process of developing the maps, the map team’s advisory committee — composed of community leaders and state, regional and federal agency representatives — noted  that communities might hesitate to make land-use decisions based on these floodplain data because of legal uncertainties of using — or not using — them, explained Wake. For example, if a town decides to restrict development in a floodplain based on projected precipitation rates and land use changes as indicated on the maps, could that restriction be challenged? On the other hand, can a town be held liable for failing to restrict development in a flood-prone area?

Upon identifying this need for more legal information, NHSG/UNH Cooperative Extension water resources specialist Julia Peterson coordinated efforts between the map team and legal researchers at the Vermont Law School to address five research questions — four of which involve legal authority and consequences, the fifth being the options and tools towns have to reduce the risk of flood hazards.

The report states that if towns have more up-to-date information about expanding flood zones, they can better prepare and thereby reduce threats to health, property and infrastructure from flooding. In fact, FEMA encourages communities to adopt more stringent regulations beyond minimum federal requirements that reduce flood hazards through a program called the Community Rating System, it adds.

The bottom line: as long as towns are using sound planning principles and a transparent decision-making process, their chance of litigation remains low, Wake explained.

Peterson said the team is currently trying to figure out the best way to get this information out to the communities who have the maps, but she believes the combination of the maps and legal report will help offer guidance and increased comfort level for community leaders faced with land-use decisions.

“This report empowers communities by helping to build confidence and competence with regards to floodplain management under current and projected conditions,” said Peterson.

For more information about the report and the maps, visit http://100yearfloods.org or contact Julia Peterson at julia.peterson@unh.edu or 2-6706, or Cameron Wake at cameron.wake@unh.edu or 2-2329.