Streams, along with stream erosion, play important parts in the development of the land all over the world. Many important events happen from the result of erosion, including the construction of waterways, erosion of mountains and other natural things, and also deposition of particles.
What is Erosion?
Erosion is the transportation of loose sediments or rock produced by weathering. Moving water is the primary agent for erosion, although ice, gravity, and wind can also cause it. The many kinds of erosion shape the land and make it the way it is today. If it were not for erosion, most of the land would not be the way it is at this time.
Gully erosion is the erosion of gullies from high velocity runoff of water. Gullies are the “bigger” or more aged form of rills. Once the process of the running water occurs, the result becomes deep gullies. When water fills these gullies, a vast amount of water flows through it, therefore carrying many particles of soil. This type of erosion forms either a scour gully or headward erosion. A scour gully is when the particles are removed from the area and deposited, then usually being disintegrated after the next water contact. Headward erosion is when the gully extends upstream as a result mostly of waterfalls undercutting the sides. The bottom picture below shows how the waterfalls form and cause damage.
Rill erosion is the erosion of recently cultivated soils, often associated with sheet erosion. It is identified by small channels, also known as rills, after a high intensity rainfall. The rills usually are about thirty centimetres deep. If the rainfall exceeds infiltration, a film will begin to be produced (sheet erosion). This begins to form small depressions where the excess water flows. The flowing water soon removes all loose particles, therefore causing other particles to be transported down the rill. Rill erosion is most common in agricultural land, forming on cultivated fields and pastures.
Sheet erosion involves the removal of a layer of soil by either a raindrop splash or water run off. It most commonly takes off the top layer of soil. Sheet erosion is hard to detect at first because the results are not very noticeable. This is often overlooked until the subsoil is exposed. When this occurs, the soil is often compacted and/or removed. After this occurs, a small layer of film begins to form. This film is usually about two or three millimetres thick. When this type of erosion occurs, the soil becomes somewhat impermeable to air and water, causing the vegetation to die off for the time being.
Stream bank Erosion
Stream bank erosion is the direct removal of banks and beds by flowing water. Typically, it occurs during periods of high stream flow. It is sometimes confused with gully erosion (erosion of gullies). Flowing water causes lateral erosion. Lateral erosion is simply the erosion of the sides of a stream. When this occurs, sediments often fill the stream, later to be deposited elsewhere. This excess is often caused by heavy rainfall, which then overloads the stream. Areas with poor vegetation are especially susceptible to this erosion, mainly because the velocity and water content are so great that it causes excess run-off. Headward erosion is when gullies erode themselves far back into hillsides. This process occurs at the end of tributaries.
Wind erosion is the deposition and movement of soil particles caused by wind. This occurs when soils that are bare from any vegetation are exposed to high wind velocities. The wind, travelling at great speeds, picks up the soil particles and carries them in suspension. Particles that range from .1-.5mm in size are transported by saltation (particles moving in a bouncing or hopping fashion). Particles greater than .5mm are moved by rolling, known as soil creep. This type of erosion is most visible during the suspension. The particles being carried are often deposited onto roads or across fences.
Erosion is a major factor in the world these days. Without erosion the landscape all over the world would not be the way it is today. The many different types of erosion each play their own important roll in the environment. Running water shapes the land and transports material. It also deposits loose sediments, which form many things. Wind transports particles a long way. The velocity of it sometimes has capabilities to carry loose particles very long distances. These particles then form things or cause “disturbances,” such as the sediments being deposited on roadway. Erosion can sometimes cause bad events to happen, such as water eroding so far into areas that people are forced to move out. These are all natural events and for the most part cannot be avoided. Erosion is mostly predictable, but sometimes not. Since it is usually predictable, people can sometimes avoid being a victim of an erosion catastrophe, such as not live in an area where stream erosion might effect your lifestyle and force you to move out. Maybe in the future more will be learned about erosion and the effects of it.
“Alluvium”. Encarta Encyclopedia. CD-ROM, 1999
Class Notes. 1999/2000.
“Erosion”. Encarta Encyclopedia. CD-ROM, 1996