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    Re: Illinois drainage
    From: Frank Reed CT
    Date: 2005 Nov 22, 01:56 EST

    George H asked:
    "And yet, in this book, the  author, having reached the Illinois River,
    comments after passing La Salle /  Peru, that "Its water may come from the
    cold, clear depths of Lake Michigan  but ... ".  Surely not, I surmise. If
    that had ever been the case, the  watercourse would have eroded over the
    millennia to become, by now, a  torrent. Is it even hydraulically possible,
    even if the ground West of Lake  Michigan is permeable to underground flow?
    That would require the water level  in the upper Illinois to be lower, with
    respect to sea-level, than is Lake  Michigan, at 580 feet? Is that the case?"
    The Chicago River famously was  reversed in 1900. The ridge that separates
    the Chicago drainage from the rest of  Illinois was supposedly only about eight
    feet high in places, but it's dense  clay and rock so there would not have
    been significant natural seepage. Building  foundations in Chicago routinely go
    well below lake level. Did you hear about  the "Great Chicago Flood" in 1992?
    There's plenty of info on the  reversal of the Chicago River on the web, so
    I'll just point you to a google  search that works  well:
    The  top results, from the Chicago Public Library, are particularly good.
    It  is true that, today, the waters of Lake Michigan flow both east towards
    the St.  Lawrence and southwest towards the Mississippi. The flow southwest is
    not very  great though.
    42.0N 87.7W, or 41.4N  72.1W.

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