This dataset shows different flood maps with sea-level rise projections (1 foot and 20 inches), above the North American Vertical Datum of 1988 (NAVD88) along the Connecticut coastline and the adjacent inland. CIRCA research recommends that planning anticipates sea level will be 20 inches higher than the national tidal datum in Long Island Sound by 2050. CIRCA’s report on Connecticut sea level rise provided the basis for projections in Bill S.B. 7, which was introduced into the 2018 legislative session and was enacted into law as Public Act 18-82.
To view the data, zoom in on the map to your area of interest. Use the Layers menu widget at the bottom of the map window to select data to display. Different projections of sea-level rise/storm surge scenarios will activate automatically at different scales.
FEMA’s Limit of Moderate Wave Action (LIMWA) boundary is also shown on this viewer as a continuous red line. The coastal AE Zone is depicted on current effective flood insurance rate maps (FIRMs) with the landward limit of the zone labeled “Limit of Moderate Wave Action”. Any area seaward of the red LiMWA line is either coastal AE or VE zone and must meet new construction requirements outlined in the updated state building code. The LiMWA line in this CIRCA viewer was updated in December 2021 to reflect FEMA’s LiMWA Viewer release for New England states, including Connecticut. Click here to learn more about the FEMA Region 1 Viewer.
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Data Description and Usage
Two different sets of data are presented in the viewer. The Mean Higher High Water (MHWW) and 1 foot and 20 inches sea level rise layers are the modeled tidal water surface that has been created using VDatum (NOAA) and 2016 LiDAR topographic data. High probability areas of inundation are color shaded blue as well as low-lying areas, which are all shaded yellow. These low-lying areas need further evaluation due to the hydrologic complexity created by flood control structures, bridges, and culverts.
The second set of data, is the modeled storm surge water levels using coupled coastal circulation and wave model (FVCOM-SWAVE, finite-volume coastal ocean model with the version of the Simulating Wave Nearshore) to hindcast the 44 highest storms between 1950-2018. This model is calibrated for Long Island Sound to capture the complexity of Connecticut’s geology and landscapes and improve accuracy for effective flood risk design. The floodwater elevation for the different return periods is calculated empirically using a Poisson-GPD fit. The return period of the storm events is presented as 10, 30, 100, and 500 year flood events or 10%, 3.33%, 1%, and 0.2% annual exceedance probability storms, respectively. The anticipated sea level of 20 inches by 2050 is also added to these different flood events using the same data described in the paragraph above (2016 LiDAR topographic data). The vertical datum for all the datasets is NAVD88.
It is important to note that the 100 year flood event layer in this tool is different from FEMA’s 100 year flood map boundary for a few reasons:
- The modeled data is calibrated for Long Island Sound to capture the complexity of Connecticut’s geology and landscapes and improve accuracy for effective flood risk design.
- The FVCOM model has higher accuracy in predicting storm surge levels.
- The FVCOM modeled data only displays storm surge while FEMA maps incorporate both surge and waves.
Wave-related splash over along the Connecticut shoreline requires smaller-scale resolution modeling. CIRCA continues to work on developing total water level flood maps that include wave data for the Connecticut coast and will update tools as new information becomes available.
This information is provided with the understanding that it is not guaranteed to be correct or complete and conclusions drawn from such information are the sole responsibility of the user. Attempts have been made to ensure that this data or documentation is accurate and reliable; The University of Connecticut, nor the Department of Marine Sciences, does not assume liability for any damages caused by inaccuracies in this data or documentation, or as a result of the failure of the data or software to function in a particular manner. The University of Connecticut, nor the Department of Marine Sciences, makes no warranty, expressed or implied, as to the accuracy, completeness, or utility of this information, nor does the fact of distribution constitute a warranty.