[JohnRPollard]

The Eastern Channel has a clearance of only 58 feet. Along with the Chesapeake Channel (186 feet), those are the only heights my chart provides.

I think one of the reasons for this is the slope of the bridge. The roadway above the two designated channels is relatively flat, so it is easier to have a minimum height figure.

I think the other reason is that there are many spans and it would be very easy to confuse which is which. Given the slope between them, confusing which span you're passing under could be a big problem.

I expect there are some engineering drawings somewhere that would answer the question. But I doubt they'd ever put the info on a chart out of concern for causing a mishap.