If the lower section is going to be the sluice then how big is your pump? Looks like you're classifying from 4" to 1¼", where 4" to ¼" would work for a small 1500gph bilge pump. If you're running it off of a Honda WX15 that should be more then enough but a WX10 may not be enough to move the rocks out of the sluice.