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Harbor Dredging-Don’t get stuck in the mud!

Written By: Charlie Agro, E.I.T., Design Engineer

Erosion, transport, and deposition of soil in coastal areas is a major issue in the Cape Cod and South Shore of Massachusetts area. The erosion of soil along barrier beaches makes areas more susceptible to coastal flooding during storms, and the deposition of the eroded soils makes shipping channels and harbors less navigable. In the coastal engineering field there is a constant struggle to keep the soil where it needs to be. Solutions such as jetties, groins, breakwaters, seawalls, and revetments have been constructed to permanently stabilize coastal areas susceptible to erosion. The problem with each of these methods is the negative long term effects they have on areas adjacent to where these structures are implemented. Dredging is another method of coastal stabilization where soil is excavated in an area to make the water deeper. The spoils of the dredged material can also be used to renouirsh beaches that have been depleted as a result of coastal erosion. Dredging can be favorable in comparison to the implementation of coastal protection structures because it doesn’t interrupt the natural littoral process. The down side is that dredging projects are not permanent solutions and will require future maintenance work.

Recently there has been an increase in large scale dredging projects in our area. Last winter a large scale dredging project took place in the Cape Cod Canal, and another large scale dredging project is set to take place in Wellfleet, MA. As seen in the picture, Wellfleet Harbor has been negatively impacted by soil deposition. According to the attached article from the Cape Cod Times, the harbor is practically non-navigable for 8 hours each day (during lower tides). This causes a major issue for the town of Wellfleet because a lot of its revenue is based on commercial fishing, recreational boating, and tourism that are all centered around the harbor. The dredging project in Wellfleet Harbor is currently planned to excavate the harbor to a depth 6 feet below the mean low water line. This will theoretically provide boaters a water depth of at least 6 feet at any time and any place in the harbor. Although 6 ft of water at any tide sounds sufficient, the issue becomes how long will it take for soil to fill in the recently dredged area making the harbor non-navigable yet again.

Wellfleet harbor is just one of many harbors in Cape Cod and the South Shore of Massachusetts area that has become a navigational hazard to boaters due to soil deposition. Although dredging projects can be successful temporary fixeblog-1-photo-dredgings to coastal erosion/ deposition problems, it doesn’t take long for the dredged area to revert back its existing state prior to dredging. This can be seen from the beach renourishment phase of the Cape Cod Canal dredging project where the dredged material used to renourish the Town Neck Beach of Sandwich, MA has “disappeared” eroding back into the bay. It is the goal of coastal engineers to gain a better understanding of soil erosion, transport, and deposition in coastal areas to determine better long term solutions to protect the shoreline as efficiently and environmentally friendly as possible.

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