Answer:

The red layer includes road surfaces, roof tops, parking lots, tennis courts, etc. These are all IMPERVIOUS SURFACES - surfaces that won't let water drain through. Research has shown that streams start to show negative impacts when 8% to 10% of the watershed is covered by impervious surfaces. Over all of Leelanau Township, impervious surfaces cover only 1.55% of the land, according to a study conducted in 2004.