Slide 7 of 75
Notes:
Urban streams are often characterized as very "flashy" or "spiky" because of the increased quantity of stormwater runoff. This characterization translates into the sharp peaks that appear in hydrographs, usually expressed in a very short duration after the start of a storm.
The hydrograph shows the effects of urbanization on the flow of the Anacostia River in the Washington DC Metropolitan Area. The Anacostia is about 40% impervious. A value of 600 cfs (about 3" of rainfall) was computed for the two-year storm. As you can see, about 15 two-year storms occurred during this 18 month period clearly demonstrating the influence of impervious cover on the frequency and magnitude of stormwater runoff in urbanized areas.