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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

Flow alteration in urban streams

Alteration of natural hydrologic regimes is a consistent and pervasive effect of urbanization on stream ecosystems, as discharge patterns—the amount and timing of water flow through streams—change with urban development. Key aspects of urbanization affecting hydrology may include:

  • ↓ infiltration and ↑ surface runoff of precipitation associated with impervious (and effectively impervious) surfaces
  • ↑ speed and efficiency of runoff delivery to streams, via stormwater drainage infrastructure
  • ↓ evapotranspiration due to vegetation removal
  • ↑ direct water discharges, via wastewater and industrial effluents
  • ↑ infiltration due to irrigation and leakage from water supply and wastewater infrastructure
  • ↑ water withdrawals and interbasin transfers

Commonly reported effects of urbanization on stream flow regimes include (but are not limited to):

STORMFLOW
BASEFLOW

These hydrologic changes can reduce habitat quality in urban streams, and adversely affect stream biota. For example, high flows can scour organisms and substrate from streambeds, while low flows can reduce habitat area and volume. See the Flow Alteration and Physical Habitat modules for further details on biotic responses to these changes.


Click below for more information on specific topics

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Figure 33. Stream runoff during a dry period (Aug 2001-Feb 2002) at three study catchments: UND = undeveloped, MED = medium density residential (1.6 houses ha-1, 6% impervious), HIGH = high density residential (2.8 houses ha-1, 11% impervious).
From Burns D et al. 2005. Effects of suburban development on runoff generation in the Croton River basin, New York, USA. Journal of Hydrology 311:266-281. Reprinted with permission from Elsevier.
Figure 34. Hypothetical hydrographs for an urban stream (yellow) and a rural stream (green) after a storm, illustrating some common changes in stormflow and baseflow that occur with urban development. Other changes are listed at left.

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