How Running Water causes Erosion

Erosion occurs when elements, such as water flow or wind remove small particles of soil or rock from the surface of the Earth. These small particles are carried away and deposited in another location, leaving a degraded land, affecting agricultural production, due to the loss of fertile upper soil layers, and producing desertification in land regions. Water runoff on the surface of the ground develops when the intensity of rainfall exceeds the infiltration capacity of the ground, leading to erosion.

Water; erosional agent

Water can be an extremely effective erosional agent, especially when it pours down as rainfall and forms water runoffs along flowing paths. Rainfall begins its erosional process, since the very first time raindrops hit the surface of the ground. The impact of the raindrops hitting the ground dislodge small particles of soil and rock, carrying them away on flowing streams of water. Depending on how these streams of water produce erosion, they can be categorized into a number of distinct types of erosion.

Three types of erosion

There are three distinct types of erosion that originate from the effects of running water due to rainfall. These types of erosion are sheet erosion, which is the least severe of the three; rill erosion, which is more severe than sheet erosion; and gully erosion, which is the most severe type of erosion. During rainfall, the impact of falling drops of rain on the ground dislodge soil particles from the ground. The small particles can be ejected as much as a few feet off the ground and a few more feet horizontally away from the point of impact. When the rate at which the rain falls to the ground surpasses the rate of infiltration, water runoff develops, carrying away the dislodged soil and rock particles.

Sheet erosion

Sheet erosion refers to the removal of very thin layers of surface soil caused by currents of running water flowing on top of them. Sheet erosion if the first stage in the erosion process and it’s the least severe, since only very thin layers of surface ground are being removed. This type of erosion usually occurs over short distances. When the rain is persistent, sheet erosion concentrates into tiny channels on the ground and the runoff changes into streams of flowing water. The effects of sheet erosion are not easily noticed in the short-term; however, a significant land degradation may be perceived years later.

Rill erosion

Rill erosion is produced when small and closed channels form on the ground. The flow depths of rills may be of a few centimeters and they may develop on the slopes of very steep hillsides. Rills may form innumerable flowing water paths that cut one another and, when combined, form bigger waterways on the ground. They are more common in the slopes of unvegetated landscapes. Rills can often be the sign of major erosional soil events. Over time, rills may evolve to become larger flowing water paths, such as gullies, rivers and streams.


This type of erosion is formed by the combination of many rills, producing wider and deeper channels on the ground. Gullies are created by running water during intense storms. Gullies are like large trenches on the ground and may be from a few meters to tens of meters in depth. During their formation, rainwater cuts deeply into the soil. The eroded soil then is carried away by the flowing water, leaving a huge cut in the ground known as a gully. Gullies are very common on hillside slopes. Gullies can affect agricultural productivity when they occur near farmland.

During heavy rainfalls, streams can become extremely erosive, removing entire floodplains. The most severe eroding floods occur along streams between mountain canyons and rivers. Their erosive power increases when these streams of water reach high velocities downstream. Glaciers are very powerful erosional agents and sometimes can remove hundreds of meters of soil from land surfaces. Glaciers may carve deep mountain valleys and carry huge amounts of sedimentary soil in meltwater streams.

Vegetation determines the impact of erosion by water. Plants with extensive root systems offer more protection from erosion than those that are not strongly rooted to the ground. Deserts are more exposed to the danger of erosion than a rainforest, as the leaves and branches of trees greatly diminish the speed at which raindrops hit the ground. According to, the greatest measure to prevent erosion is adding vegetation and preserving native shrubs, trees and grasses on places that are being urbanized.