A flood is too much water in area. Like when a river, lake, or a streams overflow because it rains for days and days. This would be a flood below:
how does it form?
A flood forms when it rains really heavily in a short time period. That causes a flash flood or a flash flood warning. Melting ice and snow also causes this. Floods last long because the ground can't let the water soak in right away.
The Great Mississippi Flood of 1927. This flood was the most destructive flood for a river. It was the most destructive river flood in the United States. It had an area of 27,000 square miles and a depth of 30 feet.
How humans have prepared for this:
Humans prepare for this by watching the weather forecasts, get a first aid kit, and knowing your insulation for your house.