Mapping the Floods

Posted in Vol 13 No 2 by bsaab on April 28, 2010

Detail, Flood Insurance Rate Map, Middlesex County, Massachusetts

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They’re from FEMA and they’re here to help. Really.

In 2003, the Federal Emergency Management Agency, perhaps best known for its response to the New Orleans floods of 2005, began remapping flood plains nationwide, digitizing and updating elevational data that had remained on government maps since the 1970s, and generating new data for densely populated and high-risk areas. This large-scale government effort has several aims: to determine what properties should carry flood insurance, to produce more-accurate assessment tools for flood hazard, to create maps that can be tied to GIS databases and used as planning tools, and, at its core, to guide future development away from high-risk or environmentally sensitive areas.

As the new maps have been released over the past year, they have had sometimes dire financial and design consequences for landowners, developers, and municipalities. Being in a flood zone increases construction and insurance costs substantially, and residents and business owners in a flood zone, whether it is classified as high risk or not, are required to buy flood insurance if they have a federally backed mortgage. Government officials take the maps into account when they establish zoning and building standards, plan infrastructure and transportation, and prepare for and respond to floods. In Massachusetts, about 50,000 properties carry flood insurance, a strong indicator of the number in flood zones.

At their best, the new digital maps factor in topography, hydrology, erosion, and changes in population density, but they ignore climate-change projections. Flood-prone areas are generally defined by one of two hazard levels: 1-percent-annual-chance flood (also known as the 100-year flood) areas and 0.2-percent-annual-chance flood (also known as the 500-year flood) areas. FEMA defines a flood as a condition where two or more acres of normally dry land or two or more properties are inundated by water or mudflow. The previous paper maps were often based on 1960s- and 1970s-era US Geological Survey 10- and 20-foot-interval contour maps, with additional surveying by engineers performed only in those areas historically known to be flood prone.

The maps do not become official until the public-appeal periods expire and FEMA releases them in their final form, but their impact already is being felt across the Commonwealth even in this preliminary phase. For any new construction or substantial improvement (work totaling more than 50 percent of the purchase value of the property), developers or owners are required to build to current flood-zone standards, which usually means raising the lowest level to above the flood level. In Hull, a builder renovating an old rooming house was told that, in order to go forward with the work, he would have to elevate the house by 3 feet and place it on piers. In Provincetown, an estimated 600 properties, including the Town Hall, are being reclassified. In the Alewife area of Cambridge, more than 100 properties have been newly determined to be in a flood plain. In Newburyport and Salisbury, hundreds of properties on both sides of the Merrimack River are affected, and town officials are challenging the FEMA flood map designation. The maps have gone into effect in Suffolk and Bristol counties, and about 80 homes in the Savin Hall neighborhood of Dorchester are now officially in a flood plain.

The impact of the new flood plain maps is already being felt across the Commonwealth.

Following the law of unintended consequences, even structures intended to prevent flooding can subject nearby property owners to FEMA scrutiny. Dams, levees, dikes, and hurricane barriers need to be certified as meeting federal standards. Without this certification, properties adjacent to these public works are officially considered flood prone. In Chicopee, a 7-mile-long riverfront levee system protects the town from floods, but it has to be repaired and recertified by FEMA, at a cost of roughly $6 million, or approximately 5,000 properties will be classified as being in a flood plain. New Bedford’s hurricane barrier, a 3.5-mile-long steel and stone structure from 1966, will have to be recertified as well, and city officials are struggling with how to pay for the necessary engineering studies and recertification of the hurricane barrier. (Similarly, in parts of New Orleans, map certification will be delayed until 2011 due to the ongoing levee reconstruction project.)

As FEMA’s Mike Goetz, chief of New England Risk Analysis Branch, explained, the National Flood Insurance Program (NFIP), of which FEMA flood maps are an integral and necessary part, “tries to make risk management and assessment a part of the everyday life and calculus of communities.” The program, established in 1968, encourages communities to exceed the minimum requirements for flood plain management — building at higher elevations and buying up properties in high-risk areas to create open space. Towns and cities can participate in the NFIP’s voluntary Community Rating System and earn points that reduce their flood insurance premiums. Goetz described its intentions: “We are trying to incentivize communities and show that doing these good things can actually not only improve the environment, but also that those who have to purchase flood insurance won’t be hit as hard financially.” Richard Zingarelli, the NFIP Coordinator of the Massachusetts Department of Conservation and Recreation, commented, “The flood insurance program does not want to burden homeowners, but we don’t want someone to take a summer cottage on a barrier island and turn it into a mansion.”

Thus far, FEMA mapping methods have not been without controversy. At this time, 92 percent of the US has been mapped by the agency, but only 21 percent of the country has maps that fully meet FEMA’s own data quality standards, according to a recent report from the National Research Council. The report, which the Research Council produced at the request of FEMA and the National Oceanic and Atmospheric Administration, argued that the agency could more accurately determine flood risk with newer mapping technologies such as LIDAR (Light Detection and Ranging), which measures elevation using aircraft-mounted lasers. Even more significantly, it noted that the maps must be continually updated to reflect natural and development-related changes.

The findings of the National Research Council point to a larger issue lurking in the muddy waters of the $1 billion FEMA project. Flood plains are dynamic entities, constantly shifting, with every new development producing runoff and erosion capable of impacting rivers and streams for many miles downstream. Just as the original FEMA flood maps of the 1970s were intended to be revised regularly but instead were left in place for 30 years due to the exorbitant cost of sustaining a massive, ongoing, nationwide mapping project, the new maps — already less accurate than they could be due to the reuse of outdated maps — will become increasingly inaccurate as time goes by. According to Zingarelli, “The intent is for the mapping to be a continual, ongoing process,” but this depends on funding from Congress. The maps’ inaccuracy over time will be accelerated by climate change, as sea-level rise (which some current predictions put at 6 feet by the end of this century) will affect not only shoreline sea levels, but also inland river and stream beds and hurricane frequency and severity.

To address these issues, FEMA has launched the next phase of its mapping project: Risk MAP (Mapping, Assessment, and Planning). It has begun to use LIDAR in coastal areas and along rivers and levees to produce more accurate maps, and now has fairly extensive data for parts of New England. As Goetz explained, “Risk MAP is being used to plan mitigation activities: it might mean purchasing flood prone areas (as a community or city or region), or elevating buildings. We’re not trying to add levees and dams. We’re trying to do fairly soft mitigation techniques with less impact on the environment.” In addition, FEMA is beginning to think about stormwater management as an issue that extends far beyond the flood zone itself, taking “a more comprehensive and holistic look at what’s happening in a watershed.”

The proactive, watershed planning approach FEMA is advocating suggests that, in order to keep up with the changing landscape, perhaps it is time to consider new, alternative modes of occupying the water’s edge that are capable of withstanding change and water infiltration. Architects, engineers, and landscape architects may be able to provide guidance and insight into the issue. American Institute of Architects’ Latrobe Prize winners Catherine Seavitt, Guy Nordenson, and Adam Yarinsky, the co-authors of the forthcoming book On the Water: Palisade Bay, have begun to investigate new ways of building on the waterfront. In their publication, they introduce the concept of “resilience,” a strategy focused on soft infrastructure such as constructed islands, reefs, piers, and wetlands that can absorb the impact of natural disasters. (Their work inspired the Rising Currents project and exhibition at the Museum of Modern Art.) As Seavitt explained, “Reframing the debate can create openings for action…. It is interesting to think that you can design something in such a way that it becomes beautiful, or a great amenity to a community, and somehow goes beyond the arguments or the entities that are there. More than just a strategy for mitigation or adaptation, it’s giving something back that’s even better.”

2 Responses

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  1. joseph said, on January 29, 2011 at 3:57 am

    Where are the flood plain maps simply showing?

  2. bsaab said, on January 31, 2011 at 10:13 am

    @joseph, FEMA maintains a solid online library of maps. Try the ‘flood maps’ link on

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