DEED-MAPPER-USERS-L ArchivesArchiver > DEED-MAPPER-USERS > 2000-10 > 0972907429
From: John Lyon <>
Subject: [DMU] A matter of geology
Date: Mon, 30 Oct 2000 07:03:49 -0500
Message text written by Lee Nelson:
>So, on to my issue de jour. What (if any) effect have you seen of
processes in your projects? Have streambeds changed due to erosion?
How about entire watersheds? DNR geologists here in GA tell me that
in the "peidmont" region of the state, streambeds may change (to a minor
degree) but the watersheds shouldn't.
I can certainly speak for tidewater streambeds on the eastern shore of the
Chesapeake Bay. In many cases this isn't much of a secret, as several
well-known colonial landmarks are awash or well under water nowadays.
Mostly this seems to be erosion or subsidence rather than actual change of
stream course. But in low-lying country this often makes a notable
difference in the land-water boundary. A fair number of early patents now
extend out into the middle of a river or creek. Early patents involving
small islands have gone poof. I've encountered only minor local changes
to waterway courses by the cutting of new channels and/or silting over of
the old, etc.
It takes a mighty heave of Nature - or geologic time - to change
watersheds. But one can see in the Mississippi - easiest on Landsat
imagery - the dramatic influence of old floods (and probably earthquakes
like the amazing New Madrid event early in the 19th century) on the River
course, with old oxbows now prime bottom land, but still very visible from
above. The Corps of Engineers has slowed this process down - or at least
changed how Nature gets her licks in.
|[DMU] A matter of geology by John Lyon <>|