I was actually responding to a previous post seeking information on these -- 
the term is unfamiliar to me, but it sound like you're more knowledgable 
than I on this topic.  We documented a crib dam on the Rappahannock River, 
and found a number of these and other dams documented at HABS-HAER. The 
concrete dam that had inundated the crib dam was an Ambursen dam -- very 
interesting in itself, but completely off-topic [we -- the Corps of 
Engineers, with the help of an Air Force demolition unit, blew the concrete 
dam up and now the Rockfish can spawn upstream for the first time in over a 
century)
Tim T.