Tutorial:Water Erosion

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SASSA Home Page ⇒ Soil & Sediment Tutorial Home ⇒ Weathering and Erosion ⇒ Water Erosion

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Contents 1 Processes of Water erosion 1.1 Rainsplash 1.2 Sheet flow 1.3 Rills and Gullies 1.4 Stream/river erosion 1.5 Coastal erosion

[edit] Processes of Water erosion

Water is a powerful force for the weathering and erosion of rock and soil material.

[edit] Rainsplash

Erosion is caused by the impact of raindrops hitting the soil surface. Although the large volumes of soil material may be moved in this way, particles can only be moved a few cm’s causing on-site redistribution, only on steep slopes will there be a net downslope movement. Rainsplash can give the soil surface a dimpled appearance.

[edit] Sheet flow

If rainfall arrives too quickly for it all to infiltrate, particularly if the soil is already saturated or frozen, the excess rainfall will flow downhill over the soil surface as run-off. True-sheet flow, in contrast to concentrated flow in rills and gullies, can only move very fine particles.

[edit] Rills and Gullies

As run-off moves downhill the microtopography of the soil surface causes overland flow to concentrate in depressions. This results in preferential flow paths that concentrate flow further increasing the potential of the water to detach particles and resulting in the formation of rills and eventually gullies.

In extreme cases gullying can result in the formation of badlands.

[edit] Stream/river erosion

Streams and rivers erode their valleys in three ways. Down-cutting into the river bed deepens the valley and can create paired terrace sequences. Lateral bank erosion in meandering river systems affects the outer edge of a [meander>Main.Glossary.M.Meander] and can act to widen a valley and cuts across floodplains resulting in unpaired terrace sequences. Finally, there is headward erosion whereby valleys are extended upstream towards or beyond their drainage divide.

[edit] Coastal erosion

Most erosion along the coast occurs through wave action, the impact of the water and compressed air within breaking waves can dislodge fractured rock and other loose particles, whilst particles in the water act to abrade the shoreline.

The shore is also subject to physical, chemical and biological weathering processes; exposure to sea water results in salt weathering, and repeated wetting and drying causes water-layer weathering extending from the low to the high water mark. Many molluscs and other creatures also weather and erode rocks by boring into them either physically or chemically.