Sediment is eroded from the landscape, transported by river systems, and eventually deposited in a lake or the sea. For example, the Fraser River carries an average of 20 million tonnes of sediment a year into the marine environment. The sediment cycle starts with the process of erosion , whereby particles or fragments are weathered from rock material. Action by water, wind, glaciers, and plant and animal activities all contribute to the erosion of the earth's surface.
Fluvial sediment is the term used to describe the case where water is the key agent for erosion.
Natural, or geologic, erosion takes place slowly, over centuries or millennia. Erosion that occurs as a result of human activity may take place much faster. It is important to understand the role of each when studying sediment transport. Any material that can be dislodged is ready to be transported. The transportation process is initiated on the land surface when raindrops result in sheet erosion.