Have You Heard the Hammering? Emergency Dam Repairs
Have You Heard the Hammering?
Work progresses on the dam! I’m delighted to report that something is at last being done to ensure the most dangerous part of this embankment is made safe.
What has worried me for many months is the electricity pylon mounted right on the edge of the crest, (the towpath), and underneath it, there is a huge leak. Cat-tails and Red Twig Dogwood abound in the swampy ground, another good indicator there is a real problem here. If there was a breach, not only would there be a massive flood, the pylon would slide off the side off the slope and pull down the power lines.
The NYPA obviously realised the dangers of moisture not flowing under the toe of the dam as it should be. See diagram below.
The dark area is where the natural seepage of water soaks into the embankment. It flows under the toe of the slope, leaving the dry soil intact.
In the diagram above, the Phreatic Line is above the toe, which allows the dry soil above to slide over the wet, (below) causing a breach and subsequent flood.
The NYPA have contracted out the job of pile driving steel sheets some 40 feet long into the crest of the dam. These panels are approximately 2 feet wide, and they are installing this wall about 100 feet either side of the pylon.
Above – Here’s a 40 feet sheet being placed above the shallow trench.
The backhoe used for the trench.
Here’s the pneumatic pile driver on it’s side. It takes this monster about 20 minutes to hammer a sheet into the ground.
Welding two sheets together.
Here’ the first 2 days worth of pile driving. They’ll hammer them down about 2 feet below grade level and then back-fill the trench. It looks like the horizontal H girder is there simply to line up the sheets and will probably be removed before they drive them to below grade level.
This close up shows how the sheets are tongue and grooved so they interlock together, An indicator that this steel wall is preventing leaks.
Notice the line of sheets is very close to the canal, which leaves me to believe that the NYPA’s main objective here was to divert seepage below the Phreatic Line, stopping a potential breach.
I hope this demonstrates clearly how dilapidated and unsafe this embankment is.
It’s been a few weeks since I walked down the towpath from 31F, and I was surprised at the amount of trees that have been toppled in the recent storms.
This tree was very close to a deep gulley, which would make a breach very possible.
I saw at least five new large trees either felled or with large limbs detached. Some of the trees are six feet diameter,, rotted at the base so badly you can see right through them. They are over 80 feet tall and at end of life. They are a disaster waiting to happen.
I had permission to enter the site, but I have noticed numerous people actually climbing through the barriers and heard several were actually arguing with workers about passing through. This is a very dangerous site! Employees will not discuss the project with you, so just stay away and let them get on with the job.
The next stage of this operation is the removal of all vegetation from the slopes. They will be cut flush with the ground and depending on size the root balls will be ground up, or buried. The numerous gulleys will be infilled and finally grassed over as per FEMA recommendations. This could take several years to complete. So we are at the early stages of this work to ensure our canal is safe for everyone living under the embankment.