If you live near a river or stream, you know water levels rise and fall without concern. It’s always wise, however, to keep an eye upstream, wary of conditions that can cause waterways to breech their banks and flood low-lying regions below. Watch for persistent rain and thunderstorms, and excessive spring snowmelt. Also, be aware of debris or ice jams downstream that can cause flooding in areas above.
Those living along the coasts are trained to watch the moon, the barometer and weather maps. The highest tides occur during new and full moons, when the combined gravity of the sun and moon pull most upon the seas and oceans. Combine these high tides with low atmospheric pressure and wet and windy weather, and you have the recipe for coastal flooding.
Flooding during a storm surge is extremely dangerous, capable of inundating large coastal regions. When a hurricane strikes land during a new or full moon, the high tide, the winds, the waves, and low atmospheric pressure combine to create a surge that can flood areas lying as high as 20 feet above sea level.
When rain or excessive snowmelt accumulates over several days, or severe rains fall over a short period of time, normally safe areas away from lakes and rivers can become flooded by rising water tables. Even homes on hillsides are susceptible to basement flooding when heavy rains become rivulets running through streets and yards.
Flash floods are characterized as raging torrents of muddy waters ripping through riverbeds, urban streets, mountain canyons and desert washes. They sweep away most everything in their path, including cars, livestock, homes and people. Flash floods can occur within minutes or several hours after torrential rains, or after the sudden break of a debris or ice jam.
As if summer wildfires were not damaging enough, they often deliver a second wave of destruction, ironically, in the form of flooding. When a hillside or mountain has had extensive fire damage, waters from a normally harmless rain or thunderstorm collect in the “burnscar” and come crashing across highways and into buildings and homes as violent, black floods.