Deposition is the geological process where material is added to a land (or a landform). This can happen in many places, such as a beach or river. Some parts of a shoreline build up and grow out, whereas other parts of the shoreline erode and fall into the sea.
In deposition, wind and water lay down grains of material that have been eroded and transported from another place. Deposition happens when the forces which transport sediments are weaker than the forces of particle weight and friction. This causes a resistance to movement, and the particles drop down.