Gloucester High School
Flood Protection Project

GZA was retained by the City of Gloucester to provide engineering design, permitting, bid, and construction phase services for flood protection improvements for the high school facility. The objectives of the project were initially to provide short term-flood mitigation but soon expanded to reduce the risk of increased flooding associated with predicted sea level rise and coastal storm frequency and intensification. Constraints on the project included: available funding; maintaining a public walkway along the canal; use of school facilities including athletic facilities; highly compressible underlying soils, an Activity and Use Limitation (AUL) associated with contaminated soils, minimal aesthetic impact to views, etc.; schedule and permitting; and consideration of “back door” flooding impacts.

One of the unique aspects of the project as it relates benefits to the New England environmental industry includes the well thought out balance to mitigate the hazards of coastal flooding and associated risk for important public assets, public safety, and infrastructure (current and those associated with climate change) with the need to permit and implement a flood protection project in a cost-effective and timely manner. This was accomplished by careful consideration of flood protection height based on the ability of the compressible soils to support a cost-effective solution as well as predicted back door flooding that would occur regardless of the proposed flood protection system along the canal.

The Effects of Climate Change and Sea Level Rise

Sea level rise and more frequent and intense storm events caused by climate change are issues threatening many areas of New England, leading to more severe and frequent inundations of coastal areas. These flood events can devastate entire communities, cause extensive property damage and disrupt local economies. Implementing cost-effective, environmentally sensitive and resilient infrastructure, such as flood protection systems and/or other shoreline protection systems is crucial in protecting communities. GZA’s design of the flood protection system was based on consideration of the Client’s objectives; our coastal flood modeling and metocean data analyses; and technical understanding of the relevant physical, economic, regulatory, and environmental site constraints. GZA’s flood protection design elements included: installation of 1,441 linear feet of steel sheet pile floodwall with modified segments to span shallow utility crossings and a bent plate cap, landward scour protection, installation of earthen levees, existing fence line modification, pavement restoration, professional landscape design, plantings, and access improvements.

As previously mentioned, the poor subsurface conditions at the Site as well as the back door flooding potential, and other factors limited the height of protection to less than the FEMA Base Flood Elevation (BFE) with the typical 3 feet of freeboard in the “AE Flood Zone”. However, the Project provides the following protection:

The implications of the above estimates are that the System will provide flood protection, except for wave overtopping, up to the 100-year recurrence interval in 2070. It is important to note that at that point, back-door flooding would inundate the protected area unless additional work to mitigate such flooding is performed. In addition, scour protection and a gravity drainage system was included on the landward side of the flood wall to manage wave overtopping. For higher recurrence intervals in 2070 or so, internal drainage including potentially a pump station could be used to help manage excessive overtopping as an adaptive measure.

Rock-filled Gabion mattress on landward side used to protect against overtopping and manage overtopping flow

Additional Information

The GZA project team demonstrated waterfront and flood protection engineering expertise by identifying vulnerabilities, using a risk-based approach to characterize the flood hazards, effectively communicating the corresponding implications to the Client, and successfully obtaining required environmental permit authorizations. GZA also identified an Activity and Use Limitation (AUL) associated with the presence of impacted fill at the Site and provided Licensed Site Professional (LSP) services to fulfill regulatory requirements. GZA assisted the City in securing a $2.4M grant for coastal construction services from the Executive Office of Energy and Environmental Affairs Dam and Seawall Repair or Removal Program that was used to fund the project. Some of the additional challenges GZA encountered and managed during the design and construction phases were the presence of several deep Horizontal Directional Drilled utility bores and frequent shallow utilities, relatively thick compressible organic soil deposits overlying very dense glaciofluvial deposits and rock, and construction access limitations.

The project was completed in the Summer of 2023.