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Questions about the Dam removal project

(87 posts)
  1. spatny
    Member

    I'm concerned about the Dam removal project. Here is what Wiki says about the Hoffman Dam.

    "Hoffman Dam, also known as Lyons Dam is a gravity dam. Its height is 6 feet with a length of 240 feet. Its capacity is 156 acre feet. Normal storage is 156 acre feet."

    My questions are: If the dam is removed or notched and this 156 acre feet of water goes on down the river, what will be the effect on the river above the dam? How much will it be reduced in width and depth? Will Coonley Bay exist? How wide will the river be, and how wide will the exposed banks be and what will they be like? I took pictures today all along the river from 26th Street to the Little (Weir) Dam which is slated for total removal. The banks all along are mostly made of rubble - broken concrete, brick, etc., and will that all be exposed. Surely, the water level will drop - but who knows how much?

    Will we be left with a mere trickle (comparatively) in times of low water? Remember, the Indians used to walk across right upstream of the Little Dam. Now, right today, there is a large pile of rubble sticking out of the water just below Hoffman Dam. When it is removed, what will we be looking at? Will there be wide, muddy banks full of dead trees carried there in time of flood? Will we have mud flats or broad swampy banks of visible rubble? When the river rises and inundates these areas - as it surely must - will it recede and leave stagnant pools to breed mosquitos? Will you be able to cross these muddy, marshy banks to get to the river?

    What will happen to the purportedly toxic material that is supposed to be behind the dam, and is probably now covered by silt? Will this be removed and trucked away? Will the broad river view we now have at the Scout Cabin be gone? Does anyone know, for sure, what the river will be like when this transpires?

    How will this help flood control? Presumably the same amount of water will flow into the river at time of storms, melting or flood. Won't the river rise to the same height it does now? What will the river be like along Maplewood? These, and many more questions need to be looked at before this monumental change to our familiar environment goes forward.

    I'm not saying it shouldn't be done, but all of the above should be clearly and irrefutably explained to the residents before we destroy something that is irreplaceable. The Corps of Engineers has not been infallible in the past, and the river as we know it is the thing that makes Riverside what it is.

    I have not heard any explanation of how, in times of storms, less water will flow into the river. I believe that if the same amount of water enters the river, it will rise just as it did before. When it overtops the walls or berm that contain it, it will flood, just as it does now. before. How will removing these dams change that situation? Answers please? Thank you.

    Posted Thursday Sep 9, 2010 16:35 #
  2. JamesMarsh
    Member

    Ask Gorman. He seems to be taking all the credit for the dam removal.

    Posted Thursday Sep 9, 2010 23:30 #
  3. ChrisHajer
    Member

    These pictures are from Spatny:



    Posted Friday Sep 10, 2010 09:41 #
  4. spatny
    Member

    Yesterday I walked along the river bank from 26th street to the Little Dam - where I could get access. The banks are mostly rubble and construction debris. After speaking to the Army Corps of Engineers this morning I learned that the river level will drop considerably. On a day like today with the water guage below the dam at 3.2 ft - almost four feet below flood stage - the lake-like lagoon above the Hoffman Dam will be gone and wide (20-40 ft.) mud flats covered with construction debris, junk and dead trees will be exposed. The more I see of this project the more I think it will be a disaster for Riverside.

    I was told today that the effect of mitigation of flooding by this removal is very minimal. This whole project is about ecological concerns - enabling fish to get past the dam and supposedly removing some toxic waste from behind the dam. Both of these are specious claims - won't invasive species also get on up the river? And just how will this purported toxic waste, now covered by silt, be safely removed? And to where? I requested the engineering report but I'm going to need some help to check it out. Any volunteers?

    If this project will do nothing or next to it to prevent flooding, and in fact will still flood periodically as it does now, why are we moving to destroy the appearance and maybe the health of the river? I wonder how the people that live along the river now will like it when the river goes down and the debris is exposed, as stagnant pools and marshes impossible to get to breed mosquitos and the smell of the river bottom pervades their back yards.

    Remember this - with a 50 ft wide breech in the dam the river will lose 156 acre feet of water that it now contains. We better look at this very carefully.

    Posted Friday Sep 10, 2010 10:20 #
  5. TS
    Member

    Being a homeowner that is impacted by flooding, I welcome the removal of the dam. The removal of the dam along with other initiatives is an effort to reduce the flooding I and others experience. There is not one project that will magically stop the flooding in Riverside. However, a number of projects together will help alleviate the damage done to our homes. Taking out the dam is one part of an overall plan.

    Posted Friday Sep 10, 2010 10:58 #
  6. JohnM
    Member

    Don stated:

    If this project will do nothing or next to it to prevent flooding, and in fact will still flood periodically as it does now, why are we moving to destroy the appearance and maybe the health of the river?

    If you take a bit of time to research the topic, you'll find that, despite what Don posits here, dam removal is one of the most effective means of enhancing both the health and appearance of a river. Dam removal has been used to great effect throughout the country--here's a link to a 1999 report that includes some comprehensive case studies-- http://www.americanrivers.org/assets/pdfs/SuccessStoriesReport6f14.pdf

    While the main purpose is not to alleviate flooding, it seems that this will--when taken in the context of an overall plan--have some impact, which I'd think is a benefit we can all get behind.

    I'm not suggesting that this not be discussed and that we ask no questions. However, it seems to me that the dam serves no useful purpose at this point--it doesn't generate electricity, it doesn't power a mill, it doesn't do anything. There is no reason that we shouldn't embrace this opportunity to restore our river to what it could be, while doing something that can help alleviate flooding in the bargain.

    Posted Friday Sep 10, 2010 11:25 #
  7. TS
    Member

    What should not be overlooked is the safety factor. Dams of this type are lethal. I look forward to being able to canoe past the Scout Cabin without fear of the dam.

    Posted Friday Sep 10, 2010 11:35 #
  8. spatny
    Member

    Everyone may be right - I'm wading into the reports I'm getting - electronically - from the Army Corps. Three large PDF files, so bear with me. I did see this - no mention of flood control.

    Based on communication with the various project stakeholders, a summary of project
    goals, as MMI understands them, is as follows:
    • To restore the areas upstream of the existing impoundments to a free-flowing aquatic
    ecosystem, allowing the Des Plaines River to flow unobstructed from the Devon
    Avenue Dam to the confluence of the Illinois River.
    • To provide for fish passage from the lower reaches of the Des Plaines River to at least
    the Devon Avenue Dam.
    • To improve the biodiversity and quality of the aquatic communities in the Des Plaines
    River through alteration and/or removal of dams, with supplemental environmental
    amenities such as wetland, stream, and pond restoration.
    PRELIMINARY DESIGN REPORT
    DES PLAINES RIVER RESTORATION
    JANUARY 2002; REVISED MAY 2002 1-6
    • To alleviate stream bank erosion on the banks of the Des Plaines River through
    proper channel design and stabilization.
    Secondary Goals
    • To improve safety conditions, particularly in the area surrounding the Hofmann Dam,
    where a number of drownings and injuries have occurred.
    • To make use of the recreational opportunity at Swan Pond and maintain it for active
    and passive recreation and preservation.
    • To improve aesthetics and public access in the areas surrounding the Fairbanks,
    Hofmann, and Armitage dams.

    I also see where it predicts about a two foot drop in water level at Salt Creek. The shape of the bottom of the river will determine how much it recedes - but I'll guess that translates to some pretty big mud banks being exposed on both sides. I'll try and copy this stuff and post it here.

    Posted Friday Sep 10, 2010 12:07 #
  9. spatny
    Member

    I found this, which doesn't seem to match with their tables...

    "The elevation of the water surface immediately upstream of the Hoffman Dam
    would drop about seven feet with removal of the dam. This would return the river (upstream of Hoffman
    Dam) to an approximate 3-foot depth and more like its original pre-settlement condition which is shallow
    water running over an exposed bedrock bottom."

    So what will be left between the stream and those concrete walls?

    Posted Friday Sep 10, 2010 12:53 #
  10. spatny
    Member

    I just got to opening the drawings for the riverbank construction above Hoffman Dam and down to the Swan Pond. It takes time to read and digest, but based on what I've read so far this project looks to do a lot for the river area - if the numbers are correct. I still don't see how the river can lower three feet at Salt Creek and not change at all north of Forest, but maybe someone with a proper background can explain that.

    This will be a quite extensive re-do and from many aspects looks like a great improvement. One thing is troubling - it mentions we may lose mature trees due to construction and the regrading of the Swan Pond. Hopefully this will be minimal. They talk about resculpting the shape of the river banks and using some technique where they "shoot" willow branches in to pin it down and they grow. I've always though weeping willows look great alongside any river - probably the largest tree in Riverside - perhaps 5-6' in diameter is an old willow near the water across from Fairbank Road. Willows - by their configuration, also help reduce sound coming across from Ogden. We could use some to help mask the sight and sound of Chicago's newest crosstown expressway - First Avenue.

    Posted Friday Sep 10, 2010 16:18 #

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