Boston Harbor Flood Barriers

The Feasibility of Harbor-wide Barrier Systems Report of 2018 concluded that the cost of a harbor-wide flood barrier system combined with the problems of building and operating such a system precluded them from recommending it at this time. (The authors based their design upon the premises that the barriers would not affect shipping or pleasure craft uses of the harbor.) This should be re-evaluated taking into consideration the construction of the TMTs and by revisiting the basic assumptions of the report.

First, the barrier would be constructed utilizing the TMT tunnel spoils, eliminating the cost of constructing hard concrete barriers. The new made land would be sculpted to blend in with the existing islands. With the amount of tunnel spoils available, other necessary filling could be done for flood protection along the coast, recreational or shipping purposes. Use of the tunnel spoils almost eliminates the second largest cost of the flood barrier system.

Next, the openings in the flood barriers can be reduced in size. These are estimated to be 60% of the cost of the flood system. The size of the openings would be designed to restrict the water flow into the harbor to eliminate normal sea level rise flooding. The movable barriers would only be used for storm surge. This could reduce the size of the barriers by half and dramatically reduce their construction and operational expense. While this will have some minor effect on shipping and recreational use of the harbor, it would be an insignificant burden compared with the protect obtained by the city.

The report assumes that the main movable barrier at the entrance of the harbor must be over 1,500 feet long based on minimum shipping canal requirements of the Army Corp of Engineer. In the face of massive flooding anticipated by sea level rise the Army Corp would probably consider a smaller entrance to the harbor.

The Cape Cod Canal shipping canal is only 480 feet wide. It handles 14,000 ships per year. Over 80% of all commercial shipping entering Boston Harbor is destined for the Chelsea Creek petroleum tank farms. Chelsea Creek is only 400 feet wide at its widest. It narrows down to only 100 feet in some areas. The Post-Panamax ships (for which the Conley Terminal is being enlarged for) are designed to pass through the Panama Canal whose locks are only 180 feet wide.

So, a much smaller harbor opening can work (albeit with some traffic management) and thus the size and cost of the movable portion of the flood barrier could be reduced substantially.