ABSTRACT
Running water dominates fluvial environments, which are widespread except in frigid regions, where ice dominates, and in dry regions, where wind tends to be the main erosive agent. However, in arid and semi-arid areas, fluvial activity can be instrumental in fashioning landforms. Flash floods build alluvial fans and run out on to desert floors. In the past, rivers once flowed across many areas that today lack permanent watercourses.
