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CADDIS Volume 2

Urbanization - Hydrology

Flow Alteration in Urban Streams

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

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

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

STORMFLOW
  • Increased high flow frequency (Figure 33)
    [Roy et al. 2005, Schoonover et al. 2006, Brown et al. 2009]
  • Increased high flow magnitude (Figures 33 and 34)
    [Rose and Peters 2001, Burns et al. 2005, Schoonover et al. 2006]
  • Increased flashiness or rapidity of flow changes (Figure 33)
    [Roy et al. 2005, Schoonover et al. 2006, Chang 2007]
  • Decreased high flow duration
    [Rose and Peters 2001, Poff et al. 2006, Chang 2007]
  • Decreased lag time (Figure 34)
    [Arnold and Gibbons 1996, Changnon and Demissie 1996]
BASEFLOW
  • Decreased low flow magnitude (Figure 34)
    [Finkenbine et al. 2000, Rose and Peters 2001, Kaufmann et al. 2009]
  • Increased low flow magnitude
    [Burns et al. 2005, Riley et al. 2005, Poff et al. 2006]
  • Increased low flow duration (Figure 34)
    [Roy et al. 2005, DeGasperi et al. 2009]
Figure 33. Stream runoff during a dry period (Aug 2001-Feb 2002) at three study catchmentsFigure 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.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.

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.

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