Notes From an Environmentalist, Potential Unintended Consequences of Removing a Dam.

   Tough Choices on Removing the Ipswich Dam

Our problem is not so much the dam on the Ipswich River but that upstream the river has a fairly wide watershed with natural floodplains.

Below the dam we have an artificial canyon of manmade walls and no floodplains except the parking lot behind Zumis, where three seals were playing during the January 13^th floods.

The problem is that the artificial canyon of manmade walls focuses floodwaters so they scour the bedding below the Choate and County Street Bridges.

After the Mothers Day Floods receded there was a six-foot deep, hundred foot long sandbar of material that had been scoured from beneath the condemned bridges.

We wont know how badly the County Street Bridge was damaged during the January 13^th floods until the floodwaters recede and state divers can get down there and look. At the rate we’re going that might not be until February.

While they are at it I’m sure the divers will also inspect the Choate Bridge, and we might have two bridges closed the way we did in 2006.

Models were run to show how the river would behave during a 500-year flood both with the dam intact and with the dam removed. Such things are becoming more frequent. We have lived through at least three 500- year floods in the past 20 years.

The models showed that the flow of water would be more than enough to scour under the bridges but they failed to predict that the bridges would be damaged.

Other states have had similar problems and have proposed re-routing their rivers to avoid having them flow through such narrow gorges. In Ipswich one path to pursue would be to divert a portion of the river from the dam to the Basin so you would have a small herring stream flowing through town.

The problem is that there is no easily accessible pot of money to alter a small river like ours. Our only option is to take the money to remove the dam and run the risk of losing our bridges or run the risk of not availing ourselves of the environmental benefits of removing the dam. Tough choices, indeed.  

https://iopscience.iop.org/article/10.1088/2634-4505/abe639#:~:text=The%20unintended%20consequences%20of%20dam%20removal&text=Major%20changes%20to%20the%20groundwater,unintended%20consequences%20of%20dam%20removal.