When using a sluice box in streams where you expect to find flakes and, just maybe, nuggets, you can run about three inches of fast water through the sluice. On Clear Creek, however, we have a lot of flour gold and you're going to lose it out the end of the sluice if you run it with fast water.
Although you may trap and recover gold flakes, fast water in a sluice on Colorado's Clear Creek will cause the flour gold to become suspended in the flow and it will not have time to settle behind the riffles. Because we do not recover much in the way of larger flakes and nuggets over a quarter of an inch in Clear Creek, but do have an abundance of flour gold, you should adjust your sluice box to have only about two inches of water running through it with just a small wave over each riffle. The sluice may be even with the water or only tipped at a very slight angle of just an inch or two over the entire length of the box.
Prior to using your sluice, classify your material down to 1/4 of an inch. Use a trowel to feed the classified material into the sluice, two full trowels at a time. Then wait a minute or two for the material to run through the box before adding more.
You will not lose any gold if you run your sluice box this way in Clear Creek. True, you won't be moving as much material through your box, but will have all the flour gold and any flakes or nuggets that come along, too--it all adds up!
The way you know that your sluice is full and should be washed into a 5-gallon bucket, is when you have black sand packed behind the riffles and beginning to cover the carpet.
To check to see if you are getting all the gold you expect, fill your pan with the tailings at the end of your sluice and check them for any gold you might be losing. With this method, you are not likely to find anything that was not trapped.