![]() The general rule of thumb is 1" drop per foot of length of your box. The perfect flow allows the gold and other heavies to drop out of suspension and the lighter material to flow out of the box. On the flip side, too little flow, while allowing the gold to drop out quickly, also allows lighter material to drop out, filling the space between your riffles, eliminating the slow spots entirely, and allowing the rest of your gold to flow right out of the box. While the lower layer is rolling behind the riffle, the upper is flowing right over the eddy, and while the eddy itself can slow the upper layer some, it's not as effective as the riffle itself. The science might be tricky to explain, but basically the upper layer of water is not affected by the riffles as much as the lower layer. Too much water, moving too quickly will carry gold higher in suspension. Getting the flow right is the key to running a sluice. The gold drops out of suspension as the water slows on the back side of the riffles. Material is placed at the top of the box and carried in suspension down the channel. Each riffle creates an eddy, a backflow of water that allows the gold to settle out. Sluice boxes work by essentially creating a straight, consistent channel, with regularly spaced slow spots created by riffles. Anywhere the water slows, material will drop out of suspension and that's where the gold will be. These irregularities mean the water flows at different speeds at different points. Even the Los Angeles River, in its concrete channel, has seems in the concrete, bridge footings, bends, shopping carts and other debris, side channels joining the flow, etc. Rivers flow through channels with irregularities, rock outcroppings, bends, narrow spots, wide spots, intrusions of bedrock, etc. Rivers aren't like plumbing pipe, with smooth walls to guide the water at a consistent speed. Gold settles wherever the water slows enough to allow it to drop out of suspension. That means the material is suspended in, and flowing with the water. This material is carried downstream in suspension. Stand by a river in flood stage and you can often hear the larger rocks and boulders bouncing down stream and cracking into one another. So the force of flood water is enough to pick up and carry not only silt, sand and gravels, but also gold, large rocks and even boulders. The Rogue River in flood nearly matched the mighty Mississippi for water volume!!! All that water driving down a narrow canyon moves pretty much everything it comes across, gold included. To put that in perspective, the normal flow of the Mississippi River at New Orleans is 600,000 cubic feet per second. The mark is about head height and the river is.way down there?!?! The Rogue River reached 500,000 cubic feet per second at Agnes during the '64 flood. Many go from peaceful little creeks to raging torrential rivers.Īt one spot on the Rogue River Trail in Southern Oregon, you hike past the high water mark from the famous 1964 flood. Most mountain streams undergo major transformations during the spring thaws, and times of heavy rains. ![]() ![]() A single gold bar in Fort Knox weighs about 42 lbs, but if you're just starting out you might not consider that, in order for gold to concentrate where it does in a stream, it must first be carried by water. We all know gold is heavy - really heavy. To understand how sluice boxes work, you first want to think about how gold deposits in the river. Powered equipment is fun too, but nothing beats a sluice box for production in lightweight, hand-fed equipment. Sluices also have the advantage of being hand fed, non-powered equipment, so no gas to pack, no smoke to inhale and no noise to spoil a quiet afternoon on the stream, plus the added advantage of far fewer regulations. With relatively little equipment to pack in, a prospector can move a lot of material and develop a good amount of concentrates in a day. Running a sluice box is one of my favorite methods of prospecting.
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