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Where Did All the Streams Go? Effects of Urbanization on Hydrologic Permanence of Headwater Streams
Citation:
ROY, A., H. R. Lubbers, K. M. FRITZ, AND A. L. Dybas. Where Did All the Streams Go? Effects of Urbanization on Hydrologic Permanence of Headwater Streams. Presented at Annual Scientific Symposium of the Ohio River Basin Consortium for Research and Education (ORBCRE), Oxford, OH, October 25 - 26, 2007.
Impact/Purpose:
To inform the public
Description:
Headwater streams represent a majority (up to 70%) of the stream length in the United States; however, these small streams are often piped or filled to accommodate residential, commercial, and industrial development. Legal protection of headwater streams under the Clean Water Act has been under scrutiny in recent court cases, leading to renewed interest in the extent of non-perennial tributaries and their connections to downstream navigable waters. In Hamilton County (Cincinnati), Ohio, we assessed 1) the extent of ephemeral, intermittent, and perennial stream channels, and 2) the effects of urbanization on the location and length of these streams of varying hydrologic permanence. We randomly selected 150 of the 6,686 stream origins mapped on Cincinnati Area GIS for field assessment. Of the points visited, 63% had no stream channel, primarily because they were piped downstream. We determined the average catchment size necessary to support stream channels (0.05 km2 ± 0.01), intermittent flow (0.11 km2 ± 0.03), and perennial flow (2.38 km2 ± 1.15). In forested landscapes, the catchment areas for stream channel origins were smaller than origins in developed areas, reflecting the loss of stream channels in urban areas. Land cover did not explain much variation in the location of intermittent and perennial streams, suggesting that other variables (e.g., geology, channel slope, relief, etc.) may also be important in predicting the origin of intermittent and perennial flow. Urban land use may result in opposing influences on hydrologic permanence, thus confounding the relationship with land cover. For example, while impervious surfaces may decrease flow permanence by reducing rain water infiltration, septic outflow pipes and stormflow pipes may increase the permanence of flow in urban streams. We need to better understand how human alteration has affected stream permanence, as this has direct consequences on the health of headwater streams and their downstream waters.
