What causes urban drainage problems?
One hundred and fifty years ago, our region was covered by dense evergreen forests. Only a small amount of the rain ever reached the creeks and rivers. Much of the rain evaporated from the forest canopy without ever reaching the ground. A large portion of the rainfall was taken up by the trees and shrubs (transpiration), and significant quantities of the annual rainfall seeped deep into the aquifers. As our area was developed, the forests gradually became neighborhoods, schools, shopping centers, and roads. Each year, a little less rainfall evaporates, is transpired by trees, or percolates into the aquifers. This shift, from forests to urban land uses, has increased the amount of surface runoff and decreased the time it takes for storm runoff to reach the nearest creek, and is the fundamental cause of most urban or neighborhood drainage problems. Other drainage problems occur because the drainage infrastructure has failed due to age and/or lack of maintenance.
