The formation of a sand dune in the desert or a delta near the water is based on how sediment is dropped and arranged. this process is known as

The formation of a sand dune in the desert or a delta near the water is based on how sediment is dropped and arranged. This process is known as -  Deposition

Deposition is defined as a geological process in which sediments, soil and rocks are added to any land form. Factors like water, ice, wind and gravity transport the surface materials, resulting in building up layers of sediment.

any abiotic or biotic factor in an ecosystem that causes a population's size to slow or decrease is a limiting factor.