Setting the Proper Water Velocity through a Sluice Box

As a general rule the optimum inclination when locating a sluice box is an inch of fall per linear feet of box. This may change depending on various factors, such as water volume being used or in the average configuration, size, volume and weight (specific gravity) of the material that one is processing.

There is no exact formula to verify the right speed of water through a sluice box so as to work under all the conditions for all the different types of rifles that are used at present. Therefore, instead of giving them the formula I will try to give you an understanding of which are the effects that an appropriate speed of water may cause in the box, and also what are the effects of the use of too much or too little speed of water. This way, you will be able to act through a direct observation to make sure the sluice box will recover gold at its maximum capacity. 

When placing a sluice, if possible, it would be good to have enough flux of water to move the material through the box as fast as you can shovel it (or dredge) in it at a maximum production speed.

Most of the riffles currently used are designed so that the action of concentrating takes place behind the riffles by the increase or decrease in the speed of the flux over the set of riffles. The amount of water in action behind each one of the riffles also increases or decreases, causing an effect on the amount of water, just enough to keep the concentrating activity behind each riffle, but not as much as have the riffles totally cleaned from the concentrated material, called “bailing.”  The amount of water and the speed at which it is directed through the box directly affects the amount of material that will stay behind the riffles. When put through the sluice, the amount and the right strength of water, riffles will go half filled with material, and the material can be observed dangling and vibrating behind the riffles (concentrating) when the water flows.

If there is less flow of water directed through the sluice box there will not be enough power to get between riffles and they will be “packed up” along with the material. In these cases, there will few or no concentrating and gold recovery will be minimum. When this happens one can observe few or no vibrating activity behind the riffles and the material will not go through the box fast enough so as to allow you to shovel the material inside at a production speed not being able to fill the box completely.