City says it can flood-proof South Boston as seas rise

The city today released plans for keeping rising seas from reclaiming all the parts of South Boston that sit on fill - which is much of the neighborhood.

The plans, which stretch to 2070, call for spending between $513 million and $1 billion over the next 50 years on a series of berms, seawalls and dunes along the neighborhood's shoreline - and possibly even flood gates at the mouth of Fort Point Channel. It sounds expensive, but city planners say the work could stave off up to $19 billion in damage from floods that would far surpass the ones the neighborhood saw during this past winter's nor'easters, as sea levels rise from 9 to 40 inches due to climate change.

Ironically, some of the proposals call for even more landfill - to create dunes and other water-absorbing features that could double as parkland during sunny days.

Planners say it would be vital to work on most of the vulnerable areas at the same time. Because of the "floodways" in the low-lying parts of South Boston, much of the neighborhood would still flood if, say, Fort Point Channel got protected, but the area along Seaport Boulevard did not.

All that blue represents parts of South Boston that could flood in a storm with an expected sea-level rise of 40 inches by 2070:

Of most immediate concern, the report says, is Fort Point Channel, which already spills over its seawalls on a regular basis.

Coastal resilience in Fort Point Channel could protect over 100 buildings and 1000 people and reduce by over $300 million the expected losses at the 1-percent annual chance flood elevation with 9 inches of sea level rise. With 21 and 40 inches of sea level rise, coastal resilience measures on the east side of Fort Point Channel could be flanked from other flood pathways and must be combined with coastal resilience measures in South Boston Waterfront, Seaport Boulevard, Raymond L. Flynn Marine Park, and Reserved Channel to remain effective. ...

Flood risk is expected to increase rapidly along the channel, and there are opportunities to partner with property owners and others to incrementally implement solutions. Nearterm actions range from $3 to $16 million depending on design and consist of earthen berms and open park space. ...

Mid-term strategies are similar to near-term strategies and extend north from the 100 Acre Master Plan to Martin’s Park and south to the base of the east side of Fort Point Channel. Shoreline strategies include earthen berms and open park space. Along the existing Harborwalk, it would be possible to incorporate building structures into the line of defense or build new barriers in the water. Bridge guardrails would be converted to floodwalls. The many stormwater outfall pipes along the channel will require flap gates. Mid-term coastal resilience solutions range in cost from $56 to $73 million.

In the long term, earlier strategies can be further enhanced through expanded Harborwalk, possible increased fill and enhanced park space along the channel, long-term flood protection measures to the Arcade, and other improvements that increase the overall flood protection, social, and recreational benefits within the area. Such additional enhancements may cost around $49 million.

A modified, flood protected Fort Point Channel:

One of the more expensive parts of the proposal, because it's one of the longest, would be steps to protect the residential areas along Day Boulevard. There are two options there:

Option A includes perimeter protection of South Boston along Pleasure Bay and the seashore along Day Boulevard. Coastal adaptations would include elevating the Harborwalk along its current path or routing the line of protection down the right-of-way of Day Boulevard/ Columbia Road. It also would include converting the concrete wall along the southern edge of the Conley Terminal to a flood wall.

Option B includes berm adaptations in the Marine Park along Farragut Road rather than perimeter protection around Pleasure Bay. Along Day Boulevard, the line of protection would incorporate restored beach and dune features instead of elevating the Harborwalk.

The release of Climate Ready South Boston (41M PDF) follows similar plans for Charlestown and East Boston. City planners are also looking to launch similar efforts for the North End and Downtown and the Dorchester waterfront.