Construction Plan Changes for the Leonard’s mill Dam Project

For those of you who are new to Chemo Pond or are unaware of the ongoing issues we have had with the water level in the pond, here is a brief refresher. There are two dams on Blackman Stream between Chemo Pond and the Penobscot River. The functional one is at the Maine Forest and Logging Museum, known as Leonard’s Mill. There is a semi-functional one located about a mile closer to the pond known as the roll dam. For years, residents on the pond have placed stop logs and other materials on top of the roll dam in an attempt to hold more water in the pond. We also relied on Leonard’s Mill to place stop logs in one opening in their dam to hold back water. This was an imperfect system as we had to ask for the stop logs to be placed at the dam every year and we had to wait until they got around to it. While we waited, we lost a large amount of water from the pond and made it more susceptible to drought. In July 2017, the water level in the pond dropped abruptly over one weekend. We discovered that a person from the Department of Marine Resources (DMR) had removed all the material from on top of the dam because it was preventing some of the alewives from leaving the pond after spawning. From that point until now, CPLA has been involved in negotiations involving, DMR, the Department of Environmental Protection, the Maine Forest and Logging Museum, and the Department of Inland Fisheries and Wildlife to come to some sort of solution that protected both the alewives and their migration in and out of the pond and our water level in the pond. Last year, an evaluation of both dams revealed that the Leonard’s Mill dam was near the point of failure. The left bank crib in the left spillway, which was made of wood, was rotting away and at risk for collapse. If this crib were to collapse the entire dam could fail. This would be catastrophic not only for Leonard’s Mill but also for our water level and for the alewife migration. A solution was proposed that would do four things: replace the wooden crib with a cement one to stabilize the dam, add a rock weir either across Blackman Stream or in front of each of the two biggest openings in the dam to replace the stop logs in the dam and stabilize our water level, improve the fishway so that the alewives were more likely to use it, and lastly to remove the roll dam to make alewife migration easier. Through March of this year, this was the plan. Once the engineering plans were finalized, it became clear that changes would need to be made due to circumstances beyond our control.

Construction began at Leonard’s Mill in the past week and is expected to last about two weeks, weather permitting. We were made aware of changes to the engineering plans shortly after the Annual Meeting on July 16.

The pros of the new plan are that there will be a rock weir in front of the left bank gate permanently. This will take the place of the boards that we have had to ask for permission to be placed each year and then had to wait for them to be installed while constantly losing water from the pond. This will allow us to hold back more water earlier in the year and slow water loss throughout the summer. Also, the many leaks through the left side of the dam will be plugged to further slow water loss. This section of the dam was never mortared and had developed numerous areas of leakage over the years. The rock weir in front of the left bank gate will also moderate water flow through the gate which will lessen water scouring that removes rocks from the upstream surface of the dam.

The cons of the new plan are that we will not be able to put a weir all the way across Blackman Stream or to block the center spillway. We have been told this is because the current permit for construction does not allow any new structures to be built. A weir across the full width of Blackman Stream or one across the center spillway would be new structures. The weir in front of the left bank gate replaces the boards in the gate so therefore it is not a “new” structure. In order to build a new structure, such as a full width weir or one across the center spillway, a new permit would have been required. Because of the amount of water that would be impounded by this new structure, a Level 1 permit would be required from DEP. Acquiring this type of permit is exceedingly difficult, can be expensive and is time-consuming. We could have protested the reduced size of the weir and insisted that the Level 1 permitting process be done so we could attempt to get the larger weir, but it is very unlikely that we would have succeeded. We were told that DEP would most likely not approve the permit and DMR would most likely not fund it. Also, the delays while waiting for the permitting process to take its course would greatly increase the likelihood of the left bank spillway collapsing, resulting in the failure of the dam.

The best option appeared to be to go along with the updated construction plan and get the work done this year. There is still a plan for a dam commission to monitor the dam, build up a reserve of money, and oversee any repairs to the dam in the future. CPLA will have a seat on this commission. This way we can keep an eye on what is going on at the dam and participate in the decision process should any repairs be needed or if problems arise with the operation of the dam.