Rivers and waterways don’t follow the same course indefinitely. As your geography teacher will have told you back in school, rivers change course over time. This is perfectly natural, but it can cause problems in the local environment. Soil erosion can also cause problems further downstream, as we will examine in this post.
Why Do Rivers Change Course?
Water flows at different rates in different parts of the river. On one bank, water might be fast-flowing. On another, it could trickle along slowly. In a wider river, there will be various currents. This has an effect on how the river behaves. Faster-flowing water erodes the river bank, moving sediment downstream. When the water is slow-moving, sediment builds up. This causes the river course to drift in the direction of the faster-moving currents.
Rivers have been changing their course for millions of years. It was less of a problem before modern agriculture and transport infrastructure came along. Today, though, riverbank erosion can cause a number of problems.
River Bank Soil Erosion
Natural water flow leading to the erosion of the river bank is a slow process, often taking place over several decades. This is less of a problem, as agriculture can accommodate and adapt to the new course of the river. It becomes more of an issue when it affects bridges and roads.
Bridges are a simple engineering solution to the problems caused by a river traversing a valley or plain. In the old days, people had to travel significant distances to find a suitable crossing point. Today, we build bridges. A bridge is an immovable structure. It can’t accommodate a shifting foundation. So, if the river bank is eroding at a significant rate, whether this is caused by heavy rainfall or fast-moving currents, the bank needs to be protected to ensure the bridge remains safe to use.
Controlling Soil Erosion Using Geomats
Engineers control soil erosion with geomats. These form a permeable layer that allows water to pass through. At the same time, geomats prevent soil and sediment from shifting. There are different grades of geomat. Thinner geomats are suitable for slow-moving rivers whereas high-grade geomats can withstand high degrees of erosion and are used to stabilize a shifting surface.
Other Adverse Effects of Soil Erosion Downstream
Agricultural land often runs adjacent to rivers, as the soil in floodplains is very fertile. Modern farming techniques rely on widespread use of fertilizers, pesticides, and herbicides. When the soil is eroded from river banks, sediment containing chemicals is washed downstream. This can reduce the water quality in rivers, creeks, and other waterways, which has a knock-on effect on fish and other creatures living in the waterways. Much of the eroded material ends up in the ocean, where it continues to pollute and contaminate.
The Great Barrier Reef is one example of how river erosion has an effect on the greater environment. Polluted water from rivers has led to a decline in water quality around the reefs, which in turn has affected marine life.
One way to reduce the environmental impact of river erosion would be to reduce the use of chemicals in modern farming, but sadly this is unlikely to happen.