Alluvial (or fluvial) parent materials were deposited by moving water bodies such as rivers and streams. The texture of the deposit depends on the energy of the water body. Fast-moving water deposits only coarse material such as rocks and gravel. If the water velocity decreases, finer particles (sand and silt) are deposited, while fine silt and clay particles are deposited by slow-moving water such as that found associated with deltas. Alluvial type of parent material is associated with such landforms as old streambeds, flood plains, deltas, fans, and levees.
Alluvial materials often have very thick layers (strata) of different size material. This occurs over time, as the speed of the water transporting the material changes. Inside strata materials moved by water are well sorted and coarse fragments are rounded.