EFFECTS OF STORM WATER DETENTION PONDS ON CHANNEL MORPHOLOGY

Five reaches of Apple Creek located north of Appleton, WI were monitored over a four-year period to assess the effectiveness of storm water management facilities (detention ponds) on protecting downstream channel morphology. Reaches downstream of urbanization, but without storm water management were wider and deeper than those that were downstream of less developed areas. In contrast, reaches downstream of the detention facilities (and development) experienced little change in their morphologies, suggesting that the management techniques used were successful. Previous work on Morningstar Tributary in Markham, Ontario, however, showed that detention ponds with similar design did not mitigate downstream erosion. To explain this discrepancy, samples of the bed and bank materials were collected for each reach and compared to the Markham study. Results indicate that Apple Creek runs through relatively resistant sandy loam to loam banks. The bed is composed of basal glacial lake clay beneath a 3-5cm layer of sand, gravel, and mud. These results are in stark contrast to Morningstar Tributary, which flows through a comparatively non-resistant silty sand soil underlain by a mixture of silt, cross-bedded sand, and fine gravel. Based on these comparisons we conclude that the stability of Apple Creek might have been due to the relatively resistant channel materials, rather than the particular storm water management technique employed.