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CADDIS Volume 2: Sources, Stressors & Responses

energy sources physical habitat hydrology temperature water and sediment quality stormwater runoff wastewater inputs riparian and channel alteration urbanization

Stream burial

Headwater streams are key habitats in terms of aquatic ecosystem structure and function, and they comprise a significant portion of total stream miles. In urban watersheds, however, these small streams often are filled in or incorporated into storm sewer systems (i.e., piped), altering hydrologic connectivity and physical habitat within the buried streams, as well as urban drainage networks. For example:

Drainage density of natural channels was approximately ⅓ less in urban and suburban vs. forested catchments in Atlanta, GA (Meyer & Wallace 2001).

Approximately ⅔ of all streams were buried in Baltimore City, MD (Elmore & Kaushal 2008).

93% of ephemeral channel length and 46% of intermittent channel length were lost to burial and piping associated with urbanization in Hamilton County, OH (Roy et al. 2009, Figs 8 and 9). As a result, drainage areas for remaining ephemeral and intermittent channels were larger in urban areas.

Interestingly, Roy et al. (2009) found that perennial channel length actually increased with urbanization (Fig 8), although approximately 40% of perennial channels originated from pipes. This increase in perennial channel length was due at least in part to increased baseflow stemming from reductions in forest cover and evapotranspiration.

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Figure 8. Total ephemeral, intermittent and perennial channel length within Hamilton County, OH for forested vs. urban catchments. Ephemeral streams are channels with distinct stream beds and banks that carry water briefly during and after storms; intermittent streams are channels that carry water during the wet season; perennial streams are channels that carry flow all year. Numbers above bars indicate absolute and % different in channel length between forested and urban catchments.
Figure 9. Conceptual representation of how urbanization affects headwater streams in Hamilton County, OH. Dotted lines indicate ephemeral streams, dashed lines indicate intermittent streams, solid lines indicate perennial streams; shading indicates drainage area for each stream type.
Figures 8 and 9 from Roy AH et al. 2009. Urbanization affects the extent and hydrologic permanence of headwater streams in a midwestern US metropolitan area. Journal of the North American Benthological Society 28(4):911-928. Reprinted with permission.

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