Modern rivers have become large drainage channels. The rain that falls on our living area is pushed away from the drains into the rivers as an obstruction. This is because there is no more space for the rain to soak into the soil in our living areas. The result of forgetting to return the rain to the ground is the excessive amount of water flowing into the rivers, and when the limit is exceeded, the rivers overflow and flood the city. This is not good, so we have raised the sides of the river and armed them with concrete to prevent the water from overflowing. It can be said, a forceful flood control. Hence, when the overflowing; limit is exceeded, we have to accept the enormous flood damage. River overflows are caused by narrow, shallow, or slow-flowing rivers. But what I think is important is the amount of water flowing into the river per unit of time, because if it is too large, the river cannot handle the amount of water flowing into it, and it will easily overflow. The key to ...