Since before written history, man has coveted gold. He has used it to adorn his body, as currency and moulded it into the shape of his gods. Gold is heavy, heavier than most other elements that can be found on the Earth's surface. Prospecting for gold today usually means working small deposits in streams by panning or sluicing. Material from a stream bed is put into the sluice and washed down the trough with water. The riffles catch the material and the turbulence they create helps the gold settle to the bottom to be removed.
Cut three strips of plywood from the sheet, two eight inches wide and one 24 inches wide. Cut the 1-by-3-inch lumber in half to make two 4-foot-long pieces.
Screw a 1-by-3-inch piece to each 8-inch-wide plywood strip, 1/2 inch from the edge, to make the side pieces. Align the two 8-inch-wide pieces with the edges of the 24-inch-wide bottom piece. Drill pilot holes and screw the two side pieces to the bottom piece.
Cut four 24-inch braces of 2-by-2-inch lumber and screw them to the bottom of the sluice box. Place one at the top, one at the bottom, one 16 inches from the top, and one 16 inches from the bottom. These keep the plywood bottom flat.
Cut two rails, each 45 inches long from 1-by-2-inch lumber. Temporarily clamp or screw the two rails to the left and right sides of the sluice box with one edge against the bottom.
Cut five riffles from 1-by-2-inch lumber. Measure between the two rails--inside dimension--for each riffle, which will be close to 21 inches. Mark each riffle position on the rails.
Remove the rails from the sluice box. Assemble the riffles to the rails on a flat work surface. Drill a pilot hole through each rail into the riffle end and add 1-1/2-inch galvanised wood screws to attach the riffles to the rails.
Set the assembly into the sluice box and align the upstream end of the box with the upstream end of the riffle assembly. Drill pilot holes for the galvanised wood screws and add two hinges to the downstream end of the riffle assembly, one on each rail.
It is important that the slat bottoms and rails make good contact with the bottom of the box and that the slat rails fit snugly to the box sides, or material that should be trapped will be washed away instead. Add a set of removable wheels to make it easier to transport between locations. Allow the sluice to dry out thoroughly after using Seal the edges of the plywood pieces before assembly with primer and paint and it will last longer. This sluice box is four feet long and should drop 4 inches from the upstream end (where you add material and water) to the downstream end (where silt, sand and water exit, leaving gold behind). If your prospect stream has a lot of fines (small flakes of gold), you can add a piece of outdoor carpet to the bottom of the box to help catch them. This can make cleanup (collecting the gold) more tedious, but worthwhile.
Always wear safety glasses and a dust mask while using a circular saw or drill. Follow all safety precautions in the instructions that come with your power tools.