The flood wall is on the north side of the river, essentially between the Comeau and Basiliere bridges, and along Washington and Merrimack streets. It has protected the downtown from being deluged by the Merrimack River since the 1936 flood, which left the business district under several feet of water.
Regulators had set a deadline of last November for repairing and raising the 30-foot-tall wall by two feet, but granted the city an extension prior to the deadline.
The wall begins below the river bed and stretches above the level of the river.
The flood-control project has several parts. It is expected to cost $1.2 million to repair and raise the wall, $2.4 million to renovate and clean the Little River conduit, which runs underground and connects that smaller river to the Merrimack; and $1.4 million to repair the circa 1938 downtown pump station behind the Washington Square Post Office and buy three mobile pump stations.
The city estimated the full cost of modernizing the existing pump station at $3 million, so officials decided to buy the mobile units instead.
Officials have said the mobile pump stations can also be used in other parts of the city in the event of major flooding beyond downtown. The 16-foot-high Little River tunnel is partially blocked with trees and other debris, officials said.
The final $1 million of the project budget is to be set aside for engineering and contingencies, in case unforeseen expenses arise.
The city hopes to borrow the money for the project from the state’s revolving loan fund at 2 percent interest. Annual payments on the loan will be made from the city budget and a small increase in sewer rates, the mayor said.