Extreme water can come from several places
By Frits Ahlefeldt, Hiking.org

We need to know more about extreme water to protect our communities, cities and trails. Basic is that the water most often come from one or several of sources simultaneously:
- Water from above – extreme snow and rain can flood a place sudden and fast.
- Water from below – when water rise from the ground the result can come sudden or slow and have devastating consequences, rising ground water often cause mud-slides and even make houses pop out of the ground. Worse – there is nowhere the water can drain off to. So the effects can be long lasting and are very difficult to prevent
- Water from the sea – Sea surges and storm floods can cause huge tsunami like waves, that can destroy and cause destruction and erosion in hours, that under normal weather would take many years
- Water from the landscapes and rivers – places can be flooded from extreme weather days away, as rivers rise and the water start pushing through the terrain, destroying anything that stands in its way