The definition of fluvial is of, relating to, or inhabiting a river or stream, or produced by the action of a river or stream, or other flowing water. You can make your own fluvial storm and see for yourself how sand dunes may be formed and destroyed by water.
Properly label and seal the finished product to keep it from being eaten.
Fill the small, clean, glass container to about 1/4th full using fine sand or glitter. Add several small beads, pebbles or similar items to help produce a rough scape. Fill the remainder of the container with water. (To eliminate any air bubbles, slightly overfill the container.) Carefully secure the lid.
Gently swirl the container. Then slowly swirl until only the finest sand is still swirling. Stop swirling. Observe the sand as it settles and creates a landscape inside the jar. Slowly swirl the container in the opposite direction. Change directions before the sand has completely settled. Repeat using faster motions.
Observe what happens to the landscape. Does the sand behave differently around the larger pebbles or beads?