Comparison of Historic vs. Current Cross-Sections at Watts Branch Station

Historic cross-sectional area = 30.4 ft2

Current cross-sectional area = 70.3 ft2

Note: Cross-sections have been overlayed for illustrative purposes only. Actual sections do not share same datum.

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Notes:

Both anecdotal evidence and field research support the notion that the larger and more frequent discharges that accompany watershed development cause downstream channels to enlarge, whether by widening, downcutting, or a combination of both.

This graph compares past and current stream channel cross-sections in Watts Branch, an urban stream in the Maryland Piedmont that has been the subject of considerable development and study for more than 40 years. The historic cross-section is from 1953 (approximately 5% imperviousness) and the current cross-section is from 1999 when the impervious cover in the watershed had reached about 30% impervious cover. It is interesting to note that this channel enlargement occurred despite the fact that nearly half of the watershed development over this time period was built with two-year peak discharge controls.