The position of flood debris, mostly river worn wood, perched on the top of housesized rocks, and the massive undercut banks showed that in flood this river would be horrific.
(the massive undercut banks; showed; that in flood this river would be horrific) Context(the massive undercut banks showed,List([98, 131))):(this river; would be; horrific; T:in flood)
the massive undercut banks showed,List([98, 131))
the massive undercut banks this river
showed would be
that in flood this river would be horrific
horrific T:in flood