Dredging is currently taking place in Boston Harbor to maintain the shipping channel near its narrowest point off Castle Island. This seems to occur every three to four years. Since several rivers flow into Boston Harbor -The Charles, Mystic, and Neponset to name a few- a great amount of sediment flows into the harbor over time. This can build up and create underwater obstructions that could damage the hull of a ship, or at least get it stuck. This problem can be fixed via dredging- a process of basically shoveling underwater rocks and muck out of the channel to keep it deep and wide. If you pass by Castle Island, you will likely see a barge with the big yellow crane pulling up rocks and muck off the bottom. Sometimes a tug boat comes along to move the barge around.
Buildup of sediment is a particular problem with the Mississippi River, which as a strategic port, needs to be dredged regularly given all the flow from the great plains watershed ends up in it.
Here is a chart clip of the general area being dredged- the end of the inner harbor and the start of the outer harbor. As you can see, the channel is very narrow in these areas, and depths of less than 10 feet occur just a short distance from the edge of the channel- especially on the South side near Castle Island. In order to safely accommodate cruise ship and cargo ship traffic, these channels need to be kept wide, and at a depth of generally at least 40 feet. Remember to be careful when boating in this area due to these dangers- see our post about the dangers of Boston Harbor for more details!www.charts.noaa.gov” and please see terms of service at “http://www.charts.noaa.gov/