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  • Writer's pictureLori Dee

Reading a River


How to Read a River


There are many good places to look for gold and I hope to talk about many of them. But first, I want to cover rivers because that is the place where you have your best chance of finding gold. Rivers, streams, and creeks all function the same, just with varying amounts of water.


Previously, I explained how gold erodes out of a lode deposit to end up in a river. I should point out that this also applies to desert areas where there is no water currently flowing. Dry gulches often get washed out and can even flash flood with enough rainfall. Some desert areas may not have been desert thousands of years ago.


It is important to learn how water flows in various conditions. If you understand what is happening in your river, you will know where to look. You might even discover someplace that no one else thought to look because they don't understand what you are about to learn.


As a general rule, water will try to flow downhill in a straight line. If it has no obstructions to divert it, that is what it will do.


The speed of the water is determined by the slope of the river channel, not by how much water is in it. A small amount of water can move very quickly down a steep slope, (think about raindrops on a windshield). Large rivers of water will sit almost completely still on near-level ground.


The faster the water moves over land, the more erosion it causes. A fast-moving river will cut a deep and narrow channel fairly quickly. It has a lot of force and can carry rocks and sediments with it as it travels downstream. As the slope of the river bed becomes less steep or less wide, the water has less speed and less force causing the heavier sediments to drop to the bottom. As the sediments build up, the bottom becomes less steep or creates sand and gravel bars that divert the water flow to the side. This will cause the river to meander from side to side. As obstacles like boulders divert the current to one side, the river will start developing bends and turns. The current is slower on the inside bend, which allows more sediment to drop because the flow has less force. As the river bed becomes flatter still (almost level), the water slows to a crawl and has almost no power, and the course of the river will follow the low points in the terrain, instead of cutting through them. With no power to carry them, heavy sediments will settle to the bottom.


Aerial view of Colorado River

Remember that gold is very heavy. Nineteen times heavier than water and twice as heavy as lead. That means it takes a lot of force to push it along the bottom of a river. Consequently, gold will try to travel in a straight line. If the water speed or power changes, it stops carrying gold and other heavy items because it lacks the force required.


So we need to know what causes the water to slow down. Obstacles. Big boulders in the river will cause the water to flow around it. That causes an eddy current behind (downstream side of) the boulder. Always look behind boulders. Any place the river widens, causes the water to slow down. Often you will find rocks grouped up in that area, showing you where to look. If the water slows, it drops its heaviest material, and that is a good place to search.


Gravel bar formed where creek widens

Another factor that is not always obvious is a change in the slope of the river bed. If it is steep, and then flattens out, the water will slow down and drop its heaviest materials. Sometimes, the bedrock on the river bottom is raised a little. That will slow the water flow. Frequently where rapids have formed, if you look carefully at the shore, you may see signs of a rock outcrop or mountain ridge pointing at those rapids. The ridge or outcrop extended out into the river bed where it was worn down through erosion. But the raised bedrock underneath caused rocks to stop in the slower water, and as they piled up, rapids were formed. Always check the rapids.


If you find large rocks on the shore sticking out into the water, look at how the water flows around them. Look for eddy currents that flow in any direction that is not downstream. If a rock points downstream, the gold will be dropped on the downstream side. But if the rock points upstream, it blocks the flow, so the gold will be dropped in front of it on the upstream side.


In the image below, I found no gold on the downstream side (right). The gold was in the pool in front of the rock ridge. I also found gold where I am standing, because the rocks forced the water (and the gold) over to this side of the creek.


Rock outcrop extends out into the creek.

In the image below, the river has deposited a sandbar on the inside bend because the water flow is lower on the inside of a curve. Remember that sand is light and gold is heavy. A sandbar is a sure sign that the water was not moving very fast and had little power. A good rule of thumb is that the gold you find will be the same size as the material you are digging. So any gold in a sandbar would be very fine, even tiny. If you want chunky gold, look in heavy gravel. If nuggets are still found in your area, look for them under and around big rocks.

Sandbar on inside bend of a river

Water will try to flow in a straight line. The very river, stream, or creek that you are scouting, flowed in almost a straight line at some time in its ancient history. As it eroded rocks, sand, and gravel, those materials got dropped somewhere in the river where the water flow was disrupted. As those materials build up into a gravel bar, they begin to divert the water flow. The river must now flow around the obstacle causing a bend in the river, and the water slows down, causing more material to be deposited. Because material gets deposited on the inside of the turn, the gravel bar gets bigger, pushing the river further over to the outside and making the bend even bigger. This can continue until the river bend is like a horseshoe, almost flowing into a circle.


Of course, terrain features will guide how the river flows. You could be standing where the bend first started a thousand years ago. Try to imagine the river in its past when it was a raging flood. Look at the image below. At one time it flowed in a straight line.


When you are scouting a river, pay close attention to how the water flows. Remember that fast water washes gold away and when the flow changes, the gold drops to the bottom. Try to find these "drop zones". If you see the water flow acting strange, try to determine what is causing it. There might be a boulder underwater that is changing the flow. If you see a gravel bar or sandbar, try to see if you can figure out why it is there. Is it inside a bend, or in a wide spot, or maybe a change in the bedrock? Now you know where to look. Good luck!


 

All content Copyright 2021- 2024 - Lori Dee


 


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