When the sea loses energy, it drops the material it has been carrying. This is known as depositionWhen material is deposited or left behind, eg when a river loses its energy and is unable to carry its load any further, or waves move sand onto a beach but lack the energy to carry it away.. Deposition can occur on coastlines that have constructive waveWaves which help build up material on the beach. They tend to have a low frequency and strong swash..