Challenge
The National Hall site is located in a Historic Design District (HDD) in Westport, CT. Located on the western bank of the tidal Saugatuck River, the historic buildings are vulnerable to coastal flooding. The office complex has experienced flooding from localized intense precipitation (LIP) in the past, which results in flooding from onsite stormwater and stormwater that flows onto the site from off-property, upstream areas.
Solution
GZA performed engineering analysis to characterize the current and future flood hazard and evaluate the flood risk at an office building in Westport, CT. GZA conducted a review of existing flood hazard data from several sources including the Federal Emergency Management Agency (FEMA), U.S. Army Corps of Engineers (USACE), and the National Oceanic and Atmospheric Administration (NOAA) to determine the flood elevation at the site for storm events with various recurrence intervals. GZA also relied on 2-dimensional numerical flood modeling results for LIP flooding, completed for a Resiliency and Recovery plan developed for the Town of Westport, CT to determine the flood depths for precipitation related flooding.
GZA reviewed federal and state regulatory codes, design standards, and local guidance to determine requirements for flood protection and mitigation measures. GZA used Connecticut State Sea Level Rise (SLR) projections to determine the impacts of climate change on future coastal flood elevations.
GZA utilized information from site reconnaissance and survey data collection to perform a vulnerability assessment of water entry points and essential building systems. GZA identified vulnerable building systems and water entry points that are expected to be flooded by the present day local intense precipitation event, present day coastal flood event, 2050 coastal flood event, or 2070 coastal flood event, based on the project’s planned service life.
Benefit
GZA recommended flood elevations to the design team to for the present-day flood hazards, as well as coastal resilience design elevations for future flooding. We are currently (as of August 2022) preparing a flood mitigation alternatives analysis that will identify flood mitigation measures to prevent flooding from entering the building interior and protect critical building systems located within the building.
