about an inch of water flowing over the riffles...and since your after fine gold go ahead and classify down to about the size of the height of the riffles...3/8" 0r so 1/2 is fine.About one inch of drop per foot depending on volume of water available. Bring some split shot with you drop some on the flare you want a round piece of shot to roll over your inspection matt and land in the first drop behind the first riffle..thats what I do and I catch very fine gold. lead will move farther than gold due to spcifiv gravity so gold will tend to settle out before lead.You can also make some lead shavings as it will act like fine gold if you can catch it you are good to go.Use the lead as a tool to familiarize yourself with the way heavies are acting in your sluice...and don't lose sleep worring about losing fines...contrary to what some here will say stream sluices such as Keene, Jobe, proline etc....work very well at recovering gold....and do your full clean up at home as your more likely to lose fines panning into a creek when you clean up...especially when panning Cons.