Slope erosion, or hillside soil erosion, is the process whereby soil on a surface that has an incline is worn away by natural forces such as water, wind or even anthropogenic activities. Erosion is more pronounced in sloped areas since the force of gravity works on the soil particles causing them to move and making it quite difficult for plants to fix themselves to the ground. This may result in landslides, loss of soil, low agricultural yields, and water pollution with soil constituents.
In all agricultural, urban, and forested environments, slope erosion does not only cut down on land productivity but also has social and economic costs. For example, in a slope, the topsoil loss leads to lower agricultural productivity, lowers biodiversity, and causes floods in downstream areas. Therefore slope erosion control is important for proper land use and management. This is especially important because even more erratic rainfall due to climate change is expected and it will lead to additional stress to the already fragile systems.
What are the Causes of Slope Erosion?
Water Runoff
The driving force behind the erosion of slopes is mainly water. The rainwater cascading over a slope causes soil particles to shear off the surface hence the formation of rills and gullies over time. In many instances, especially during downpours, drops of rain striking bare, attained soil surfaces may be very erosive, in a ‘splash erosion’ effect, detaching loose soil aggregates which will subsequently be removed by effective water flow.
Wind
Where there is little or no vegetation cover, wind can also be the cause of erosion when there are loose soil particles. It is however more effective on flatter terrains than on steep slopes but wind erosion itself can still contribute to loss of soil.
Human Activity
Activities such as construction, logging, overgrazing, and improper methods of agriculture diminish the integrity of the soil, making it more prone to erosion. In particular, the removal of trees and other plants enhances the potential for soil displacement while construction may also cause the loss of fertile soil layers that protect the underlying earth.
Gravity
It is a well-accepted fact that gravity alone drags the soil down the slope in the absence of even water wind or any other external forces. This is more obvious in cases of landslides when the mass of soil gets moved suddenly in a large quantity.
Effective Methods to Prevent Soil Erosion on Slopes
Terracing
There are several ways to prevent erosion but Terracing is one of the finest methods. Terracing means constructing step-like formations on slopes to prevent water from running off the surface and losing soil to erosion. In general, terracing consists of splitting the slope into a set of flat or slightly inclined areas which helps in reducing the velocity of water flow and creates safe zones where plants can be grown. Terracing in agriculture has been embraced extensively, particularly in hilly areas. Besides controlling soil erosion, terracing enables agriculture in marginal areas by providing additional cultivable land.
Vegetation Cover and Ground Cover Plants
Among the various methods applied to control slope erosion, one of the most beneficial is vegetating the slopes. The roots of plants help to hold the soil in place, and in so doing, help to reduce the amount of soil that is washed away. Trees, shrubs, grasses, and other ground-cover plants are used for such purposes quite often. This is considered one of the best methods for preventing soil erosion on a slope.
Grass and Cover Crops
Deep-rooted types of grass like fescue help prevent the soil from being washed away. On the other hand, cover crops such as clover and alfalfa grow over the ground and help prevent erosion while at the same time enhancing the soil with organic matter.
Shrubs and Trees
The establishment of shrubs and trees contributes to a firm network of roots within the soil which assists in averting any soil slips and erosion. Native flora tends to be the best option because they grow best in their environments and enhance the ecosystem by providing shelter for certain animal species.
Contour Ploughing
Contouring ploughing (the practice of ploughing along the contours of the land) is imperceptible in agricultural practices. It is because this technique enables the farmers to follow the geography of the land water runoff where the cuts are made, allowing the water to percolate into the soil instead of carrying the soil off. On its own, contour ploughing is particularly effective in minimizing the soil wash in sloped regions since it is integrated with terracing. This typically helps in slope erosion control.
Retaining Walls and Gabions
The building of restraining systems and neotextilogical usually presents denser components that help hold the soil in equilibrium against the flank slope. Retaining structures are commonly found in roads and houses built on steeply sloped surfaces while geobags are mostly found in farms and road construction. These systems are important in soil reinforcement, landslide control as well as management of moist soils by encouraging flow to control soil erosion. The cage structure can allow free movement of water thereby facilitating drainage of the causes of water pressure on the slope.
Mulching
Using organic materials- for example, straw, wood chunks, or compost, in a layer over soil surfaces helps to know how to prevent soil erosion. Mulch has a cushioning effect on the rain and reduces water run-off by increasing the infiltration of water in the soil. Furthermore, due to decaying nutrients, the soil is enhanced through the application of mulch. Mulching method is suitable for young slopes after planting since vegetative cover is yet to be attained.
Erosion Control Blankets and Geotextiles
Soil stabilization blankets are usually made of biodegradable materials (for instance, coconut coir) or synthetic geotextiles and are placed on the soil horizon for a limited period of time. They serve to minimize soil erosion and facilitate the growth of plants by conserving moisture and protecting the seeds. Erosion control blankets are used in large areas in constructions, steep inclinations, and rehabilitated green surfaces.
Diversion Ditches and Channels
Preventing erosion on slopes can look very challenging but, diverse ditches and Channels are the most effective means. The construction of minor diversion ditches or channels deflects excess water from undesirable sites, thus avoiding direct discharge down a slope. Moreover, by regulating water movement, diversion ditches minimize the chances of erosion and landslips. These features are especially beneficial on extensive slopes where the natural drainage patterns tend to enhance the possibility of erosion.
Riprap and Stone Covering
Riprap is the technique of placing stones, or boulders on the soil slopes as a means of controlling erosion in that area. The boulders dissipate the energy of moving water and therefore help to hold the soil in place. Riprap installation is commonly seen along the banks of rivers, on the slopes of cut and fill valleys, and other high water run-off sections. Some places might not be suitable for the inclusion of this technology, but it is one of the best methods in places where vegetation alone cannot be relied on to combat erosion.
Contour Trenching
Contour trenching is the process of excavating less deep than normal trenches following the slope of a hill. These trenches help conserve moisture by providing a barrier and the excess water does not run off the area. These basins help in holding the water which in turn prevents the soil from being washed away. Contour trenching is frequently applied in projects aimed at reforesting and revegetating degraded lands, especially in dry and semi-dry areas.
Check Dams
Natural drainage lines can be modified by the construction of small check dams made of rocks, log pieces, or other materials to reduce the speed of water flow and facilitate sediment deposition. Check dams slow down the movement of water over a slope hence reducing any chances of creating large gulleys. Their effectiveness is most pronounced in areas where there is a steep slope and or there is a lot of water flowing, for example after a heavy downpour.
Agroforestry
One of the ways of slope erosion control is through agroforestry, which combines trees and shrubs with crops or livestock, providing balance. Soil is protected by trees and shrubs which provide roots to hold the soil in place, and such that crops can be planted in between them. This technique minimizes erosion and increases soil fertility and diversity as well as promoting environmental and economic welfare to the farmers.
Silt Fences and Barriers
Silt fences, more often than not constructed of fabric mesh or any other semi-porous material, are usually erected on slopes or construction sites to protect soil from erosion. These fences prevent the movement of soil in water, but at the same time, allow water to flow through. This is particularly true in the silt fence when constructed in the phase of construction or landscape enhancement.
Conclusion
Preventing erosion on a slope is important mainly to maintain the quality of soils, protect the ecological balance, and mitigate risk to infrastructure and farmland. Erosion can effectively be curtailed using several techniques which include vegetation, terracing, and engineered solutions such as retaining walls and check dams. Most of the time, however, the best approach is a mix of these techniques according to the conditions of the slope such as steepness, weather, soil type, and use.
If you would like to understand how to stop erosion on a slope, then adopting these erosion control measures will help landowners, farmers, and even municipalities maintain soil health, reduce the effects of environmental decay, and enhance the landscape’s potential to resist erosion and weather extremities.’