City, feds ponder next steps for protecting Boston from rising seas, including Providence-like flood barriers

A consultant hired by the Boston Water and Sewer Commission is recommending a new barrier system where Boston Harbor meets Fort Point Channel, to keep rising sea levels and more intense storms from letting the ocean reclaim what was once South Bay - a large swath of Dorchester, South Boston and Roxbury.

Separately, the Army Corps of Engineers, which last fall released a $52-billion plan to protect New York City from rising seas, said this month it's begun to look at how to protect Boston as well - focusing on East Boston, Charlestown, the North End, Downtown, South Boston and Dorchester.

The proposed Fort Point Channel barrier, topped by a new pedestrian bridge, would have gates that would be raised as a storm approached and could cost between $459 million and $767 million, depending on configuration, the BWSC consultant, Hazen says, in a report released earlier this month.

It's expensive, but could help protect billions of dollars worth of buildings and infrastructure from the effects of climate change on our coastal city, the consultant says.

BWSC hired Hazen to look at a particular problem Boston could suffer during the more intense storms predicted over the next few decades: Many of the storm sewers that now drain Boston, which rely on gravity, could stop working and become flood generators themselves when the level of salt water rises above the height of the sewers. Once that happens, rainwater with nowhere to go could begin to burst out of the storm sewers further inland - Hazen's report estimates a third of Boston could be at risk from this sort of flooding.

The report studied 37 storm-sewer outfalls, covering about 71% of the city, and concluded that many would need moveable barriers installed over their outflows to keep surging seas out of them, for a total cost of about $568 million.

In addition to a larger system at Fort Point Channel, the consultant also recommended storm-surge barriers in the area along Dorchester Bay.

In several locations, the firm recommended that gates be coupled with holding tanks and pumps to collect water from the storm sewers - and new, higher outfall pipes to get the water into the harbor. For example, it proposed building a large tank under the grass between the arbor and the harbor in Christopher Columbus Park, along with a small building to house an electrical - rather than diesel - generator and a berm along the water. A similar setup was proposed for Logan Airport, which, like South Bay, largely sits on reclaimed land at sea level.

The Army Corps of Engineers, one of whose last major Boston-area project was to buy up several thousand acres of land along the Charles River to act as sort of giant natural sponges to soak up spring floodwater, announced its plans to look toward the sea in a Feb. 3 meeting with city officials already studying ways to minimize the effects of flooding from a combination of rising seas and more intense storms.

The Corps estimated that more than 18,000 buildings and structures in the city's harbor-facing neighborhoods could be at risk.

The Corps says it will spend the next two years working with the city and residents to figure out the specific risks to different areas and how best to prepare for them and then release a specific plan in 2026 for Congress to consider funding.

Though its Climate Ready program, Boston has already begun work on a series of short- and long-term proposals for handling storm surges.

Martin's Park, on Fort Point Channel, for example, is designed to act as a reservoir after heavy flooding and storms. Moakley Park in South Boston is being redesigned to act the same way. The BPDA last week authorized spending $880,000 to study what can be done with Long Wharf to keep the harbor from roaring in along it into downtown Boston.

The Corps's plan for New York calls for construction of a massive series of storm-surge gates and seawalls to try to prevent a recurrence of Hurricane Sandy's destruction.

Eric Bender has more on protecting Boston - and the history of the harbor.