CADDIS Volume 2: Sources, Stressors & Responses
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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