PROJECTED FUTURE DESIGN FLOOD ELEVATIONS (DETAILED)

The Massachusetts Executive Office of Energy and Environmental Affairs (EEA) developed a series of additional coastal data products from the MC-FRM to support the Resilient Massachusetts Action Team (RMAT) Climate Resilience Design Standards & Guidelines. RMAT coastal design parameters include Water Surface Elevations (WSEs), Maximum Wave Heights, and Maximum Wave Crest Elevations (MWCEs). These coastal design parameters were developed for six (6) selected annual exceedance probabilities (AEPs), including the 1%, 2%, 5%, 0.5%, 0.2%, 0.1% probability levels, and three (3) time horizons (2030, 2050, and 2070).

RMAT MWCEs (provided in units of feet referenced to the NAVD88 datum) are derived from the MC-FRM peak still water surface elevation and the maximum wave height that is projected to occur during storm events for any given location in the model domain at each AEP, and are used as a recommended design criteria in the RMAT Climate Resilience Design Standards & Guidelines Tool where projects are potentially exposed to future coastal flooding and wave action. MWCEs are computed by adding the maximum wave crest to the still water level, thereby producing the maximum wave crest elevation. In general, maximum wave heights are used for bridge design where no wave load is desired, so the MWCE may be too conservative for typical commercial and/or residential development within the project area.

For this project’s coastal design parameters, Woods Hole Group calculated Significant Wave Crest Elevations (SWCEs) based on the projected near-term (2050) and long-term (2070) peak still water elevation plus the significant wave height at the 1% AEP. The 1% AEP is a standard for building design in the floodplain. Significant wave height is approximately equal to the average of the highest one-third of waves, measured from trough to crest for a given AEP and time horizon (and is therefore lower than the maximum wave height). SWCEs (provided in units of feet referenced to the NAVD88 datum) for the project area are recommended to inform future development in this area and do not include any freeboard.