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Frank wrote:

"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."


Is "routinely go well below lake level" an understatement by an order of
magnitude or greater?   At the risk of taking the entertaining Chicago
River tours at face value (which I note have architectural factual errors--
based on my education), a least one company had gone under financially when
it's estimated of what it took to auger down to bedrock for skyscraper
pilings fell short.  Maybe 600'?

While I'm way off topic, in my three-year tenure in South Bend, IN (on the
Michigan/Indiana border) I've seen my share of sand mixed with compost
("blow dirt") over clay and poor drainage. As a side bar, some claim areas
south of Michigan City, IN were at one time in the not-to-distant past Lake
Michigan delta.  recent post seem to bear that out.

In an attempt to spin this into navigation, the lower lake level has made
some harbors inaccessible to mid 30' fin-keel and larger sailboats, and the
folks I know are going to wing keels when moving up or laterally for the
reduction of a foot, or foot and a half, in draft.  Regrettable IMHO from
the perspective of going to weather and leeway (in older boats).

Bill

   

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