nothing about waterway=flume in the osm wiki, so I created a proposal page for it:
http://wiki.openstreetmap.org/wiki/Proposed_features/flume
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HB: as long as folks are happy with waterway= instead of man_made=, it seems ready to go. see also flume_cl.
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uploaded by HB for the mainland 14 Jan 2011 in changeset 6964788