When things erode, they wear away due to some force acting on them. Just look at any coastline, and you will notice how the constant pounding force from wind and waves causes erosion of the rocky structures, leaving behind all kinds of interesting cliffs, caves and structures. Soil is not immune to erosion, and like rocks along a coastline, soil can erode due to the effects of forces, such as water, wind and farming practices. In this article, we will learn about soil erosion and the factors that cause it.
Soil is naturally created when small pieces of weathered rocks and minerals mix with organic materials from decaying plants and animals. Soil creation is a slow process, taking many years and impossible to control. However, the soil that is created is constantly subjected to natural and manmade forces that disrupt it. Soil erosion is defined as the wearing away of topsoil. Topsoil is the top layer of soil and is the most fertile because it contains the most organic, nutrient-rich materials. Therefore, this is the layer that farmers want to protect for growing their crops and ranchers want to protect for growing grasses for their cattle to graze on.
Water Erosion and Surface Water Runoff
One of the main causes of soil erosion is water erosion, which is the loss of topsoil due to water. Raindrops fall directly on topsoil. The impact of the raindrops loosens the material bonding it together, allowing small fragments to detach. If the rainfall continues, water gathers on the ground, causing water flow on the land surface, known as surface water runoff. This runoff carries the detached soil materials away and deposits them elsewhere. There are some conditions that can accentuate surface water runoff and therefore soil erosion. For example, if the land is sloped, there is a greater potential for soil erosion due to the simple fact that gravity pulls the water and soil materials down the slope, there is no controlling it. Also, water will have an easier time running across the surface, carrying topsoil with it, if the ground is already saturated due to heavy rains or the soil lacks vegetation to keep the soil in place.
There are different types of soil erosion caused by water. Sheet erosion is erosion that occurs fairly evenly over an area. As raindrops loosen soil, the surface water runoff can transport topsoil in a uniform fashion, imagine a bed sheet sliding off of a bed. This can be so subtle that it might not even be noticed until much of the valuable, nutrient rich topsoil has already been washed away. If a gardener heads out to his patch and sees an accumulation of soil and crop residue at one end of his patch, he should be worried about sheet erosion.
Rill erosion is erosion that results in small, short-lived and well-defined streams. When rainfall does not soak into the soil, it can gather on the surface and run downhill, forming small channels of water called rills. You can use this fact as a memory jogger if you remember that ‘a little rill will run downhill.’ A rill will dry up after the rainfall, but you may still see the stream bed that was created by the temporary stream.
Gully erosion can be thought of as advanced rill erosion. In fact, if rills are not addressed, they will grow into larger gullies. Gully erosion can spell big problems for farmers because the affected land is not able to be used for growing crops, and the big ditches create a hazard for the farmer driving his farm machinery over the fields.
Soil erosion can be avoided by using land within its capability. The land’s position, soil type and slope determine how vulnerable it will be to erosion. It may not be suitable for agriculture because you can not control the crops, or suitable only for an activity which limits erosion. There are a number of resources to help determine how land should be used to avoid erosion: for cropping lands and land management field manuals map and describe the land types in many districts and provide advice on land use and management for each soil type. Go to our library catalogue and search for land management field manuals to view manuals available in the state you reside in. For grazing lands, maps of soils and land types are available for most areas. These give graziers an indication of what soils their property may have and are a useful planning tool. Search for soils maps and reports in your region to prevent soil erosion.
Surface cover and runoff
Surface cover is a major factor to control soil erosion because it reduces the impact of raindrops falling on bare soils and wind removing soil particles. It also reduces the speed of water flowing over the land. Erosion risk is significantly reduced when there is more than 30% soil cover. Total cover is achievable for many grazing and cropping systems. Runoff concentrates as it flows downslope. By the time rivers draining large catchments reach the coast, they are usually just a few hundred meters wide. Even though surface cover encourages runoff to spread, runoff concentration is inevitable. The relationship between cover and soil loss coordination across the catchment is important when implementing runoff control measures. Runoff may pass through several properties and cross several roads (sometimes railway lines) as it passes from the most remote part of a catchment to a major drainage line or river.
Vegetation can be used to control shore erosion by planting appropriate grasses into the existing tidal and parameters. This strategy is generally limited to sites with very limited fetch. At sites with a larger fetch creation of a marsh fringe will require the addition of elements such as sand fill with or without some type of sill to attenuate wave action. This procedure for addressing erosion is not limited to the shore zone, but can be used elsewhere, such as on upland banks or bluffs. Various forms of bioengineering techniques can be employed to control groundwater seepage and surface runoff. Vegetation also can be used to stabilize banks or bluffs roots from plants (trees, bushes, grasses) bind soils and form a living, adaptive barrier. Vegetation can be used in combination with graded banks to provide an effective approach to reduce erosion. See more visit: Lake and Wetland Management