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.
It's a 19 1/2"x6" drum with 5/8" expanded holes it will run down over a 8x8 section of 3/8" expanded down into a water bed before dampered with a piece of rubber the sluice continues as 8" x 36" debating on added a 12"x 24" section as for pumps I want a honda but funding may cause dual 1100 bildge pumps lol