Posted on February 11, 2025
The western end of Sampson’s Island (adjacent to Cotuit) was dredged by the County over a three-year period from 2018 to 2020. Over 135,000 Cubic Yards of sand was removed and piped to the eastern end of Sampson’s Island (Dead Neck). Since this project was completed in 2020, erosion and longshore drift continued moving sand from Dead Neck and collecting it at the western end of Sampson’s Island (Cotuit). Several major early winter storms in December and January (of 2022 & 2023) breached a section of the island adjacent to the eastern jetty at the Osterville entrance to West Bay removing a high volume of sand creating a wash-over area making it vulnerable to future wash-overs during extra ordinary high tides. This area of the island is also the nesting habitat for threatened coastal shorebirds including Least Terns, Common Terns and Piping Plovers.
This project started in the spring of last year but weather delays slowed the progress and the project was suspended on April 1st when the shorebirds arrived on the island. The project was restarted in October and it was completed on December 21st.
This was a very challenging project with over 2.1 miles (or 11,000′) of pipe required. A Booster Station (pump and engine) was also required due to the distance to the east end of the island where the sand was needed. In addition, some sections of the channel had very hard packed material which also slowed down the pace of dredging.
The chart below shows the four areas dredged and the volumes dredged at each area.
This project had several benefits. The first two were the dredging of the channel to remove shoaling, and the secondary benefit was placing the sand dredged from the channel to rebuild the ‘wash-over’ area.
Besides improving the coastal resilience of the eastern end of the island, all of the material dredged helped restore the critical nesting habitat for shorebirds (Piping Plovers, Least & Common Terns). In addition, as the dredging removed several hundred linear feet of the western end of Sampsons Island, it also widened the area between the spit and the mainland thereby increasing the water flow or flushing of the Cotuit Bay.
The target or planned volume for this project was 27,500 Cubic Yards. The actual volume dredged was 23,016 Cubic Yards.
There are several reasons why we didn’t hit the target volume for this project.
The Unknowns
These are the ones that are very difficult to plan for and every project will lose dredging time due to the following:
Mechanical Problems
It’s not a matter of if it will break, but when it will break. During this project, we lost at least 5 days of dredging due to various mechanical breakdowns. When hours are lost, they usually can’t be made up as other projects in the schedule don’t allow for extra days to be added. We have to move quickly to assess the problem and get it quickly repaired. This requires having the most common spare parts on hand and more importantly, having a skilled crew to make the repairs. Fortunately for us, our Dredge Superintendent Jason Bevis is our “MacGyver” and is incredibly talented at being able to get most if not all of our problems fixed with minimal downtime.
Weather
Depending on the location, each project has different exposure to the wind/seas which can make conditions unsafe and cause dredging operations to be suspended. In some projects, the channel is protected from the prevailing winds, but a swell can be running which makes the cutterhead (the big thing that spins and sucks the water/sand mix) come off the bottom. In the Cotuit project, ten days were lost due to weather (wind, seas and heavy rain). This mostly occurred as we started working in Area 3 and Area 4.
Mobilizing & Demobilizing
The two miles of pipe that was needed for this project requires a fair amount of setup or mobilizing time. For this project, we had to tow various sections of pipe to this site from several locations. Each section had to be connected once they were in place, and they are all were secured with 250 lb. anchors to hold the pipe in position. The booster station (a large pump and engine) was positioned on our barge which had to be towed from Falmouth. Fortunately for this project we were able to keep the barge inside of the channel and it didn’t have to be moved for the duration of the project.
Excluding delays caused by weather (winds/waves) a total of seven days were required to get this project ready to start.
Yet another variable that can affect the dredging progress for some projects is the hardness of the bottom (or how hard the sand is packed). If a channel is dredged routinely (at least once in a three-to-five-year period) the bottom is usually lightly packed and can be “easily” dredged. In the southern sections of the channel (Area 3 & Area 4), the dredging progress was very slow. It was determined that the blades on the cutterhead were wearing down and slowing the dredging efficiency. When we had a weather delay, we took the opportunity to ‘install’ new teeth on the cutter head which improved the ‘cutting’ of the bottom material.
Seasons Changed
The seasons changed during the course of this project. A later summer ‘heat wave’ brought air temperatures in the mid-70’s for a week or more, then as we stated to demobilize in late December, we had to break ice with the skiffs on several mornings before moving our equipment onto the next project.
