Flash flooding is less predictable and is more life threatening than river flooding. River flooding is considered more of an economic problem as it threatens property and halts business that is often dependent upon a particular river.
Flash floods can also occur due to dam failure or an ice jam.
The aftermath of a flash flood Like a glacier deposits soil and silt as it recedes, a flash flood deposits whatever is in its way, but only after the flood subsides. The soil, streams, drainage areas, small rivers, and tributaries can usually take on the rainwater. However, these small streams, reservoirs, and creeks are not made to hold an exceptionally large amount of water. Heavy rain forces the water over the banks, and onto surfaces that aren't made for, or prepared for, such a flow of water. This could be your local road or highway, or maybe even your backyard.