How Does Running Water Cause Erosion?

How does running water cause erosion? Erosion happens most commonly through the elements water, wind, and ice. Water in the form of raindrops or overland flow can cause erosion by dislodging small particles of soil or by transporting particles of Earth in running water.

Running water causes erosion a couple of different ways. To understand them we have to establish the distinction between erosion and weathering because they can often be confused for one another. Erosion is basically the transportation of regolith from one place to another. Regolith are the loose layers of rock and mineral fragments that cover most of the Earth. Weathering is simply the abrasion of a material like rock, for instance. Erosion, then, is the transportation of the broken up parts of a material –such as rock-- caused by weathering. Simple!

Now we can better answer the question: “How does running water cause erosion?”

Running water causes erosion by two processes: suspended load and bed load. Suspended load uses the velocity of running water to carry sediment particles like silt or clay. But if there’s not enough velocity to the water then the sediment will just sink. The flow of water depends on the smoothness of the channel.  Laminar water is slow which tells you that its channel walls are smooth. Bed load refers to sediment too large or heavy to be kept in suspension; these particles move down bodies of running water by sliding, rolling or sometimes jumping short distances. Turbulent water, unlike laminar water, is fast and its channel walls are rough.

So there you have it, running water will erode by either suspended load or bed load. The higher water velocity, the larger and greater quantity of particles can be lifted while less turbulent running water carry less suspended loads.Reference

References:

National Geographic. Visualization Geology. Wiley Publishers since 1807. Murk Skinner Mackenzie 

Chapter 7 Weathering and Erosion. Section "Erosion and Mass Wasting"