Lesson 4: Human influence
So, we’ve gone through the natural processes of sediments and rivers. Let’s look at how human activities influence these.
We humans change landscapes on a massive scale – sometimes these changes are even visible from space. Despite our technological progress, we’re still trying to understand the impact we’re having on other organisms and on the landscapes around us. This is true concerning rivers and sediment processes as well.
Let’s have a look at the many ways human activities interact with sediments in river systems.
The human touch
Rivers provide us with sources of food and water, electrical energy, improved environmental quality, means of transport, visual beauty, identity and recreational activities. There’s much to understand and protect.
At the same time, humans have a major impact on rivers. We build bridges, dams, factories, harbours and power plants, and we change riverbanks and floodplains. All of these activities can affect how sediments move.
As covered before, climate change has brought about more frequent and intense rain events which not only increase river flow, but often also increase erosion and thus sediment supply.
Click on the hotspots in the image to study some of the ways human activities influence rivers and sediments
Urban spaces are sources of a wide range of pollutants that end up as sediments. These may include plastics, wastewater content, construction materials and tyre particles.
Rivers often experience high loads of nutrient input from agricultural sectors. Some of this input also mixes with natural sediments.
Bridges are useful for transport and accessibility, but their construction and presence can disrupt river properties and thus also the sediment distribution throughout.
Many of us depend on driving for everyday transport and work. Tyre-wear pollution is unfortunately a widespread problem, and sediments in rivers and ocean have already shown to contain high amounts of tyre particles.
Rivers are excellent pathways for transporting people and goods. Though, ships and boats also disrupt ecosystems and sediment structures in rivers. Moreover, various forms of waste from these are of great concern.
Hydroelectric power has massive potential in reducing our dependence on fossil fuels. However, they can disrupt vital flows of sediments and thus impact ecosystems downstream. They may also block important migratory passages for fish.
Residential suburban areas can like urban spaces yield many forms of pollutants. We need to build homes for our growing populations, but also remedy the impacts expanding urbanisation has on rivers.
Reducing vegetation near rivers can have dire consequences, not only for local ecosystems, but also for us. Plants near rivers are great modulators of swelling river waters, but if these disappear we increase the risk of floods in our industries and urban spaces.
Dams, bridges and power plants
Structures controlling the flow of rivers can affect sediment processes along large stretches of a river. Earlier we discussed how low-energy flows can lead to deposition of large volumes of sediments, while high-energy flows can bring a wide range of sediments into suspension. Upstream of dams, the water slows down and sediments often settle and accumulate.
Since the transport of sediments is blocked, downstream of dams the river is collecting new sediments to carry, which can lead to erosion of riverbeds and banks. Therefore, humans can have a massive impact on sediment distribution over a large area.
Groundwater
Another point we haven’t touched upon yet is the interaction between our groundwater systems and rivers. Water also flows underground in rock and soil layers below us, and it’s often from these reservoirs that we draw our water for consumption and sanitation. Groundwater and rivers exchange water with each other. While groundwater usually does not carry much sediment, changes in groundwater levels can still influence river levels, habitats, and the way sediments are deposited or eroded.
Transport
Rivers are not only great at transporting sediments, they also help move people and goods seamlessly through entire regions. Many industries depend on rivers for transporting goods, while recreational sailors find downtime and action on their boats. There are different ways these activities can affect sedimentary processes. For instance, the wake of a ship can stir up sediments and slowly reshape the riverbed by the redistribution of sediments and local erosion, especially in shallow areas, near banks, or around piers.
In some places, rivers are dredged to keep shipping channels deep enough, which also changes sediment transport.
Pollution
Many human activities contribute to river pollution. While some impacts are difficult to avoid completely, they can and should be reduced. Some of the major concerns include:
- Agriculture: topsoil and nutrients can enter rivers through surface runoff and erosion, especially during heavy rain. Fertilizers can also leach through the soil into groundwater, which eventually reaches rivers. The problem is worse when there are no buffer zones, like tree lines or small forest patches, which help slow runoff and trap sediments.
- Cities: urban areas produce large amounts of plastic and wastewater, much of which ends up in rivers and can harm aquatic ecosystems.
- Industry: some factories release harmful chemicals or heated water. For example, power plants often use river water for cooling and return it at a higher temperature, which can negatively affect aquatic ecosystems.
Pollutants can stick to sediment grains, which unfortunately means that sediments can sometimes spread pollution along a river.
We need solutions
As you may have realised by now, rivers are already quite complex systems, and human activities make them even more complicated. And so, we need not only the attention of researchers and experts to study and investigate the issues and challenges of river systems, but also the involvement of local people and businesses who depend on the river in their daily lives.
