Differences in the permeability of urban and rural land surfaces lead to differences in their hydrographs. Urban streams have ‘spikey’ hydrographs, that is stream flow goes up quickly during a rain storm event and then down quickly when the rain stops. Rural streams have much more ‘gentle’ hydrographs, with stream flow going up slowly during a rain storm and falling over a long period after the rain event is over.

In the next page, the accompanying animation and sound files illustrate the difference between urban and rural hydrographs. Here, we have converted streamflow data to sound files. High-pitched tones of long duration indicate high stream flow and low-pitched tones of short duration indicate low stream flow. Compare the sound files (as tones or musical instruments) for an urban stream (the Rouge River in Detroit) and a rural stream (the Sturgeon River in the Upper Peninsula). Can you ‘hear’ the rain storms?

Rouge River

Sturgeon River