Answer:
Grow if sand supplied from rivers or coastal erosion exceeds sand lost to deep water, and shrink if the sand supply is smaller than the sand loss.
Step-by-step explanation:
Sandy beaches expand and shrink over time. Sand concentrates on the beaches by several agents such as rivers, from various land areas to the seashore in the form of soil erosion, and so forth. But, sand also diminishes from the coast through the continuous stronger wave action.
Therefore, if the supply of sand by river water and coastal erosion exceeds from loss of sand to offshore water, the sandy beaches will grow, whereas they will shrink if the supply of the sand is smaller than this loss of sand.