Prospecting for Gold - Building a Sluice, High Banker, or Rocker Box - Learn About the Riffles First

Everything you could want to know about how big to build your riffles. We use them in rocker boxes, high bankers, sluices, etc. This site has all the facts and details. For instance, did you know that the deeper the riffle, the more water force required to keep it from getting packed up? Turbulence is created behind the riffle so the material should be dancing. You need to pay close attention because if the material at the bottom of the riffle isn't, you need to increase water pressure or make the riffle shorter. When you increase the water flow smaller flake doesn't settle out as well, therefore shortening the riffle is usually preferred.

It isn't a plan, but it is valuable information if you are contemplating building a machine that uses riffles. This comes from the New 49er's Gold Prospecting True Life Gold Prospecting Adventure.
http://www.goldgold.com/the-size-of-riffles-2.html