Editing DnD Desert Raiders Campaign Natural Hazards (section)

==== Flash Floods ====
Storms or spring runoff from nearby mountains can send deadly walls of water through ravines or along low desert gullies. A flash flood can suddenly raise the water level of an area, filling a dry gulch to the top of its walls. A flood raises the water level by 1d10+10 feet within a matter of minutes. Water washes through affected squares, traveling at a speed of 60 feet or more, unless impeded by slopes or solid barriers. Treat a flash flood as stormy water (Swim DC 20 to avoid being swept away). An additional DC 20 Swim check is required each round to keep the head above water. Characters who stay below the surface might drown (as described on page 304 of the Dungeon Master's Guide), See Aquatic Terrain, page 92 of The Dungeon Master’s Guide, for more about the effects of being swept away.
Along with the hazards of fast-flowing water, the flow uproots trees and rolls enormous boulders with deadly impact. Characters struck by a wall of water during a flash flood must make a successful DC 15 Reflex save or take 3d6 points of bludgeoning damage. A flash flood passes through an area in 3d4 hours.