When talking about ports, this depth is referred to as minimum under-keep clearance.
Calado is draft, as I'm sure you know and draft + under-keel clearance gives you the minimum required depth.

see
Issue. Presently, deepdraft vessels arriving and departing Hawaiian commercial ports, with the exception of non-double hull tankships, have no Federal requirements regarding Minimum Under-Keel Clearance (MUK). The State of Hawaii has established guidelines for maximum drafts and MUK for all of its major deep water ports and harbors, which are set forth in State Harbor Master Notices.
http://hosthawaii.org/sop0497.html
http://meeting.helcom.fi/c/document_library/get_file?folderI...


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Note added at 5 hrs (2010-05-04 07:55:18 GMT)
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I meant keel not keep!

and sorry, quandt, I only just noticed your answer (I was too quick with my response, as this was something I knew about). I do I agree with your answer, although I think 'under' is usually used. Especially as ports have an M.U.K. - minimum under-keel clearance.