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Mining Gravel and Protecting Streams

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Published on: Oct. 2, 2001

Last revision: Nov. 9, 2010

Owners of streamside land have always faced flooding and erosion due to natural events, but damages caused by in-stream mining should not be an additional threat to personal property.

More than 500 in-stream mining sites exist in Missouri. Considering the potential harm any one gravel mining operation can cause, it is important that gravel mining occur only with proper safeguards.

Missouri's streams are vulnerable to huge problems caused by gravel mining. These waterways have formed within their valleys over thousands of years. During this period, the stream meandered across its flood plain. Because this movement of the stream channel happens very slowly over many years, natural erosion occurs at a rate to which the stream can adjust.

The characteristics of a given stream are not formed on hot summer days when there is little water flowing in the channel. Instead, our streams are carved out during periods when the stream channel is flowing at least half full. During high flow, the water has enough power to cause changes.

Streams are a series of alternating deep areas called pools and shallow areas called riffles. Riffles are high areas of the stream bottom that control the slope of the stream. It's because riffles help control the slope of the stream that they work to control erosion.

Generally speaking, erosion occurs on outside bends and silt, sand and gravel deposition occurs on the inside bends. This process produces the sinewy characteristics that we are accustomed to seeing as we float, fish or swim in our favorite stream.

Gravel mining often results in piles or pits that, during high water events, can rapidly increase the erosive process in streams.

Although many of our streams have plenty of gravel to spare, we also have many streams which cannot afford to have gravel removed from them. To ensure you are mining from a stream that has ample gravel, look for some key characteristics. Streams with excess gravel generally have gravel bars with little or no vegetation growing on them. The rocks are generally small (less than three inches in diameter) and are loosely packed.

Gravel bars that are vegetated or where the rocks are tightly packed (not easily loosened when kicked) are characteristic of healthy streams with just the right amount of gravel. These should not be disturbed.

When practical, rock aggregate should be acquired from non-stream sources such as nearby rock quarries, but if you must remove sand or gravel from a stream or its flood plain, at least do it in ways that will not damage your property or your neighbor's property.

Without a doubt, the worst damage caused by gravel mining is the extensive erosion that results when the mining operation makes the slope of the stream channel steeper than it was before mining. When a stream channel is made steeper, the water flows faster; and the faster it flows, the more power it has to cause erosion. In these situations, the bottom of the stream channel erodes away first, and then the stream banks fall in and wash away.

If the gravel mine is a pit dug in the stream channel and the miner continues to take gravel over a long period of time, the erosion can move far upstream and cause extensive property damage to many streamside landowners. Because of these potential problems, gravel should never be mined deeper than the water elevation at the time of removal. If the stream channel is dry, mining should not be deeper than the elevation of the stream bottom at the site. If you don't mine too deep, the natural slope of the channel will not steepen, and the risk of serious erosion damage to neighbors will be reduced.

Gravel should never be removed from riffles because breaking up the riffle threatens channel stability and important habitats for fish and other aquatic life.

Gravel miners need to get their equipment through the stream corridor and into the stream channel, but the wooded corridor along the stream protects the waterways and, itself, needs to be protected. This forested area slows erosion, filters excess nutrients and sediments, baffles powerful flood flows and provides important habitat for aquatic and terrestrial plants and animals. It also protects the waterway from our other activities in the flood plain and watershed and keeps stream temperatures cooler with its shade.

When mining gravel, maintain an undisturbed buffer at least 50 feet wide at the top of the high bank and that extends for the length of the excavation site. Construct access points from the high bank into the channel to minimize erosion of both the access road and stream banks. Make sure you replant areas disturbed for access once excavation is complete.

It's also important to leave a 20-foot wide buffer from which mining equipment is restricted between the mined area and stream bank vegetation. Keeping mining equipment out of this area assures that the stream will not change its course as a result of the mining. It will also prevent eroded material from causing siltation problems downstream and will protect the roots of plants that prevent bank erosion.

When gravel mining, never relocate or straighten stream channels. Doing so can cause instability that leads to excessive erosion of the streambed and banks.

Once mining is finished, unused material should be returned to the removal site and smoothed to mimic the original contours of the bar. Unused material should not be stockpiled in the channel, placed against the stream banks or deposited in a stream side wetland. Stockpiling material in the channel obstructs high stream flow, which can increase stream bank erosion. Pushing material against stream banks may actually increase erosion at the site. Remember, any sand, gravel, silt or other sediment eroded from one place will deposit somewhere else and may cause you or your neighbor serious problems.

Water quality is always a primary concern, so fuel, oil and other wastes should not be stored in the channel. Sudden high flows from rain storms may cause spills.

Fish, macro-invertebrates and other stream creatures rely heavily on the stream bottom to maintain healthy populations. The stream bottom provides food, spawning habitat, a place to protect eggs, nursery habitat and shelter from predators. It only makes sense that gravel mining can be harmful to these stream dwellers.

The smallest particles of sand and soil carried by a stream are called "fines." This is what makes a stream look muddy after a heavy rain. Normally, these fines settle as the water level in the stream falls after a rain and no harm comes from their presence. If we do something to cause an excessive amount of fines, then the water remains muddy and the bottom may become covered with this silt, causing many problems for fish and other aquatic life. We can prevent some of the risk by avoiding mining during the spawning season.

A common practice in gravel mining is to wash the gravel to remove these fines. Sand and gravel washing as well as gravel crushing and sorting should occur far enough away from the channel so that the warm, stagnant, silty wash water cannot enter the stream. This will protect water quality and prevent sedimentation (silting) of important stream bed habitats.

Using proper techniques and safeguards, it's possible to excavate sand and gravel without increasing erosion and with little or no damage to important habitats of aquatic plants and animals. If you have questions about proper ways to excavate sand and gravel from stream channels contact the Missouri Department of Conservation for guidance and a free brochure.

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