It's the name given to the piles of stones which run perpendicular to the banks of the Humber at places like Paull. I can find no reference to the word other than as a variation of crunch. It has been used in the area for as long as I can remember.
• (v. t.) See Craunch.Found on http://thinkexist.com/dictionary/meaning/cranch/
Cranch transitive verb
. Found on http://www.encyclo.co.uk/webster/C/180
No exact match found