Flood study, with fresh approach, measures downside of pavement
Rather than soaking into the ground, the water is swept quickly into rivers and streams where it increases flood hazards. But how much of a hazard are these impervious surfaces? A new study has estimated the size of the effect. For every additional percentage point of impervious surface in a watershed — going from 5 percent coverage to 6 percent coverage, for instance — the peak of the highest flood flow of the year increases by 3.3 percent.