Local strategy map
Urban flood susceptibility index

High

The high category of the urban flood susceptibility index identifies locations that are more susceptible to urban flooding than other portions of the region. While specific locations may not currently flood, streets and buildings within these areas could be more susceptible to surface ponding, overland flow, water seepage, and basement backups. That is because the physical conditions present in these areas are associated with a higher number of reported flood damages over time.  

The highest scoring areas of the index often have a combination of factors that make them more susceptible. High scoring locations tend to be older areas of the region that were not only developed without stormwater management systems, but are often served by combined sewers. These areas have a moderate to high percentage of impervious cover, where intense stormwater runoff can overwhelm the combined sewer system. The index also identifies low-lying or flat areas where water is likely to pond, especially if the existing sewer network has reached capacity. Learn more about the index methodology here.

A range of stormwater management activities should be prioritized in areas of higher flood susceptibility. County and municipal governments should prioritize watershed and sewer modeling efforts in these locations to better understand where flooding is occurring and identify potential solutions. Partners at the state and regional scale can help communities incorporate flood risk and corresponding solutions into land use and transportation plans, capital improvement plans, as well as development ordinances. Capital maintenance, investments, and retrofits, including site-scale green infrastructure, should be prioritized to locations with higher flood susceptibility. Larger scale green infrastructure restoration and acquisition could help reduce flooding in downstream areas.

Flooding does not affect all populations equally. Exposure to flood risks appears to be greater in populations and communities already facing vulnerability due to socioeconomic, demographic, and health factors. In the CMAP region, three out of four people living in economically disconnected and disinvested areas are also living in the areas most susceptible to urban flooding. While this correlation is due to a variety of factors, there’s a clear need for stormwater investments in these locations.

Moderate

This category of the urban flood susceptibility index identifies locations that are moderately susceptible to flooding. While specific locations may not currently flood, streets and buildings within these areas could experience surface ponding, overland flow, and water seepage. That is because the physical conditions present in these areas are associated with a fair number of reported flood damages over time.

The moderate scoring areas of the index often have a combination of factors that can make them susceptible to flooding but may also have other physical assets that help to reduce flooding risk.  Areas receiving a mid-range score in the urban index are often served with separate storm sewers and may have been developed with floodplain and stormwater management practices. However, some development may still be located in low-lying areas where water is likely to pond, especially if the existing storm sewer network has reached capacity. While these areas typically have less impervious cover than high scoring locations, some areas may still experience localized flooding. Learn more about the index methodology here.

A range of stormwater management activities should take place in areas of moderate flood susceptibility. Maintaining existing infrastructure, including green infrastructure, is a priority to ensure that these systems continue to perform. County and municipal governments should work to better understand where flooding is occurring and identify potential solutions. Partners as the state and regional scale can help communities incorporate flood risk and corresponding solutions into land use and transportation plans, capital improvement plans, as well as development ordinances. Larger scale green infrastructure restoration and acquisition could help reduce flooding in downstream areas.

Low

The low category of the urban flooding susceptibility index identifies locations that are less susceptible to urban flooding in the region. These areas may have been developed more recently and are therefore built with modern stormwater and flooding design practices. These practices are more likely to accommodate stormwater within a development site. They may also have lower levels of impervious cover and are served by separate storm sewers. Maintaining existing infrastructure, including green infrastructure, is a priority to ensure that these systems continue to perform these essential services. Larger scale green infrastructure restoration and acquisition could help reduce flooding in downstream areas.