HAVERHILL — Right under the feet of downtown shoppers and workers, a hidden world exists.
In a mysterious area beneath busy Washington Square, workers are making repairs to the Little River Conduit. It’s a giant tunnel that allows the river to safely flow under downtown streets, sidewalks and buildings and into the Merrimack River without risk of flooding the area.
The 2,000-foot-long tunnel — covering more than a third of a mile — was built in 1937. It begins just north of Washington Square. Above the Tunnel’s entrance are railroad tracks that carry freight trains and the Amtrak’s Downeaster commuter train. The tunnel zig-zags in a few spots and ends at the flood wall behind the MVRTA bus station in Washington Square.
In some spots, the tunnel is big enough to drive a large truck through.
Repairs began in August — a delay of about two months due to high water levels in Little River — and are expected to be completed by the end of this month.
“They’ll still have other work to do, including landscaping (adding vegetation next spring) by the entrance of the conduit, as well as additional work on the flood wall, where some parts need to be fabricated,” City Engineer John Pettis said. “That work should completed in December.”
The massive underground tunnel is part of the city’s flood protection system, which also includes the flood wall along the north bank of the Merrimack River and a pump station. The flood wall protects the city’s downtown between the Basiliere Bridge to the east and the Riverside Place condominium building to the west.
The wall was built after the flood of 1936 caused the Merrimack to overflow, resulting in severe damage to the downtown.
In addition to carrying the water of Little River to the Merrimack River, the tunnel prevents Little River from flooding the area behind the flood wall and the properties along the original path of the river back to Lafayette Square.