Dam removal.

[gfen]

(captions belong to the picture ABOVE, not below)

Hello, dam!

If I cared, I'd tell you when it was built. Probably 1939, if the other CWA park is anything to base it on. I can tell you when it was removed, though, which was three weeks ago.

The next day, the work crew has removed all the dam and removed some of the "island" in the middle, and relocated things to the far bank. They're continuing upstream, shoring up and adding native rock structure along the CWA-made walls.

Three weeks later (or, like, this weekend), you can see the whole way up. Look, structure! Riffles! No more silty, ishty pool. The carp will need to find somewhere else to live, I guess.

Let's look the OTHER direction, for a change. Before.

The next day.

And three weeks.

Forgot a "before," but this was all once a slow, flat, section of unfishable crap. You can see where the water level was up to on the right side where a bank had formed inside the walls. None of this stcuture was there before. This is three weeks after.

The guys at Monocacy TU (who I think really got the ball rolling on this), have some more at their website, and I have additional pictures in the before/after vein over here. If you're [d]easily butthurt[/d] of sound moral fiber, just look at the pictures.

 

[Fishidiot]

Looks like a good project - thanks for the heads up. Show us some more pics a year from now.

 

[gfen]

I will, I'm interested to see how it all ends up once a good flood blows through and the banks have some time to solidify and grow in.

 

[Rolf]

Good news for a change. Thanks.

 

[afishinado]

Great post, G.

Interesting to see how it all works out in both the short and long term. I would bet the trout will appreciate the effort.

 

[ebroesicke]

thanks g.

 

[Van_Cleaver]

They removed a dam a couple years back on a local freestone stream. It's still relies on stocking, but turned into some decent riffles; especially for such a suburban stream. Smaller scale than what you showed but same result; huge forked stick, bait pool turned into actual trout water.

 

[Lonewolve]

Gary,
Was over to check it out pretty nice, still could use some things to keep the thalweg in order, below it still needs attention but nice non the less. I am tempted to go plant some willow along it.

 

[Maurice]

How in the world did they get approval to remove the dam without removing the sediment upstream of the dam first? Think about it. That dam is three feet tall, shallow pool carp water, probably 1,5-2 ft of sediment. After pics show no sediment and a nice gravelly riffle. Well thats all downstream now. I guess it woulda been anyway though.

I ain't knocking the efforts or merits of the project, more trying to wrap my head around way an agency would approve this and also make folks do pump arounds on small stream projects to prevent sedimentation.



Regarding the thalweg comment, Its a grade change/riffle. The point bar developing upstream of the dam via bedload deposit is demonstrating the rivers intent to develop some sinuosity albeit limited by the walls the This will change continually over time and unless some structural grade control is installed the entire stretch will be nothing more than a continuous riffle providing very little if any habitat for anything more than minnows and benthic population.

 

[ebroesicke]

In regards to sediment, the thinking was ( as it was explained to me) that:
the sediment exists in the system, its just blocked up by the dam pre- removal. When you release the dam, it is just distributed as it would have been if there was no dam in the first place. No sediment was created, just moved. If you visit the site you would also see that even with the current low flow, water moves through that area pretty well. They weren't releasing it into a big slow pool, only to choke that up. I had the same question when this was started.

As far as the nature of the stream bed now, I can only say that it probably needs some work, but I think it will be OK. There will soon be a push to do some plantings on the new banks to shore them up.

 

[RyanR]

It's not a large dam holding back many cubic tons of sediment load that would have detrimental impact downstream. That sediment will be transported down through & out of the system naturally now, just as it was meant to be. This area is not too far from the creek's mouth where it enters the Lehigh River, which will further carry it down throughout the system.

 

[troutbert]

What's a cubic ton?

I agree that the sediment is no big deal. It was sediment coming down from the watershed anyway. It just paused there for awhile.

I agree with Maurice that it looks like the stretch will end up being a shallow riffle. It's hard to tell everything from photos, but I don't see anything there that will cause pool formation.

The stream is straightened and constrained by the walls. So it's unlikely you will get meander bend pools. If you want pools, you'll probably have to design and build for that.

Rock cross vanes would do it.

The article mentions random boulder placements. That would help some, creating small holding areas in the riffle.

But some real pools would be better than a few small pockets. And for that you'd need some "non-random boulder placements."

 

[pcray1231]

This dam might have been too small to worry much about it. I dunno, I'll leave it to those more familiar with it than I.

But yeah, taking out a dam can ruin a stream downstream. Yeah, it's sediment that would have come down anyway, and just "paused", and will eventually get carried away. But "eventually" can be as long as decades. I see Maurice's point. Not familiar enough with the exact situation to come to a conclusion, though.

 

[troutbert]

If the stream below there has at least a moderate gradient, the fine sediment will move through pretty quickly.

That was the case with the McCoy Dam removal on Spring Creek. The quantity of sediment released was enormous.

And in the low gradient section below the dam, alongside those 2 houses, and down along the rr tracks, there was a lot of fine sediment deposited.

But it's gone now. It's hard to say what the exact time was for that to happen, but I think roughly about 3 years.

Even in that slow, low gradient section the fine sediment gets moved when the flow levels are way up.

 

[RyanR]

Decades for it to flow through the system? Hardly, not on small run of river dams like this. The first high water event or two will accomplish it. C'mon guys, do ya actually think these dams are removed without any planning? Sure some are better than others but they're all planned out. There's no denying these streams are healthier because of the removal. How many dam removal projects have you followed from start to finish? One thing I've learned is that in many cases after removal there is a period where the stream is left to define its own channel before any post-removal improvement is done, and that's often done in stages. The McCoy-Linn dam project was completed in this manner. A good friend of mine is a TU Home Waters coordinator, his job largely involves taking down numerous dams on one trout stream. For several reasons, lots of these projects are completed in stages. I congratulate the Monocacy Chapter and the City of Bethlehem and the other partners for this project. Look forward to seeing the final product.

Whether it's riffles or pools, who cares? I've never heard that a riffle isn't good habitat, especially for the all important macros.

And uh yeah, I think I was going for cubic yards there.

 

[troutbert]

RyanR wrote:

Whether it's riffles or pools, who cares? I've never heard that a riffle isn't good habitat, especially for the all important macros.

Pool habitat isn't important?

 

[ebroesicke]

^it is, and there are pools upstream and downstream from this. We are talking about 10-20 yards between pools, not a 1/2 mile of riffles. The area under the bridge in the first picture is about 5+ ft deep, and the engineer who was onsite supervising the whole project left part of the pool below the dam intact. It was to deep for a guy in chest waders. I am glad this project is getting so much attention, it is a big improvement over what it was, and it was done correctly.

 

[troutbert]

ebroesicke wrote:
^it is, and there are pools upstream and downstream from this. We are talking about 10-20 yards between pools, not a 1/2 mile of riffles. The area under the bridge in the first picture is about 5+ ft deep, and the engineer who was onsite supervising the whole project left part of the pool below the dam intact. It was to deep for a guy in chest waders. I am glad this project is getting so much attention, it is a big improvement over what it was, and it was done correctly.

What did they do to ensure that the pool below the dam will remain? Did they leave a "stub" of the dam in place so that there is still a bit of a drop there, to maintain the plunge pool below the dam?

I proposed doing that on a dam removal and was told that DEP would not allow it, that to get a permit to remove a dam, you had to FULLY remove it. You could not leave a low "stub" portion of the dam for habitat diversity, including pool habitat.

But you could come back in later and create rock cross vanes to create pools and other habitat diversity. Which seems kind of contradictory.

 

[ebroesicke]

No portion of the dam was left in- stream. There is currently nothing in-place to "guarantee" the pool will remain. I didn't mean to imply that the whole pool was intact, just that there is still a portion of deep water that was intentionally undisturbed. Only time will tell if it remains deep, but for now it is there.

 

[troutbert]

Where a plunge pool was formed below a dam, and you remove that dam, the plunge pool will disappear.

Unless there is something else going on there to create and maintain the pool, for example if the bridge abutments are influencing the flow in a way to maintain a pool there.

But generally speaking when you remove a dam, the plunge pool will disappear. That's predictable. The mechanics of it are very straightforward.