“Flash floods happen fast.”
Fairview NJ is pretty high altitude wise. Not far away is the Meadowlands which are fairly low. In Fairview cemetery there is a stream running along the bottom of a 25 foot deep streambed. The cut is just dirt but the bottom is cement. There is maybe six inches of water trickling thru there on a normal day. One day I was literally parked at the edge of that cut. I had to hug my truck to avoid falling in. Suddenly one of those monsoon like rainstorms whips up. Within seconds there is a roaring noise and the water is ten feet higher and whipping by at what looked like 30 mph or better. Fast ain’t the word. It took only seconds for that cut to start draining whatever it was draining.