[jgirard1]

On maps that show water depths, there has to be an adder to offset the current lake levels. Where can I find this information?

For example, if I look on the map and it says the water depth is 3, in actuality it's really something different. I need to know what the general offset is.

Can someone please elaborate on how this all works?

Thanks.

 

[Guest]

If you look at the chart, or the first page of the chart book, it will list the low water datum level that all of the depths are based on. I have a chart here at work from 1982 and the plane of reference (low water datum) is listed at 571.7 feet above Pointe-au-Pere, Quebec (also known as the International Great Lakes Datum, or IGLD)

Now you need to find out what the current levels are. Go to the Army Corps of Engineers site (Click Here) to see the current level. Right now it says that Lake St. Clair's June mean level is 574.5, so right now, the depth of the lake will be 2.8' (34") above the listed depths on the chart. You also need to subtract that same amount from any charted bridge clearance numbers to get the true height above the water.

 

[Guest]

QUOTE(Bill272 @ Jun 15 2004, 02:23 PM)If you look at the chart, or the first page of the chart book, it will list the low water datum level that all of the depths are based on. I have a chart here at work from 1982 and the plane of reference (low water datum) is listed at 571.7 feet above Pointe-au-Pere, Quebec (also known as the International Great Lakes Datum, or IGLD)

Now you need to find out what the current levels are. Go to the Army Corps of Engineers site (Click Here) to see the current level. Right now it says that Lake St. Clair's June mean level is 574.5, so right now, the depth of the lake will be 2.8' (34") above the listed depths on the chart. You also need to subtract that same amount from any charted bridge clearance numbers to get the true height above the water.
Very true.