Jump to main content or area navigation.

Contact Us

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

Stormwater runoff & impervious surfaces

Perhaps the most defining characteristic of urban streams is the increase in the amount and rapidity of stormwater or surface runoff to those systems. Impervious surfaces associated with urbanization reduce infiltration and increase surface runoff (Fig 16), altering the pathways by which water (and any associated contaminants) reach urban streams.

Common impervious surfaces include:

  • Roads
  • Parking lots
  • Rooftops
  • Driveways and sidewalks
  • Compacted soils

How does stormwater runoff affect streams?

It alters natural hydrology, generally leading to more frequent, larger magnitude, and shorter duration peak flows.

It alters channel morphology, generally leading to changes such as increased channel width, increased downcutting, and reduced bank stability.

It alters in-stream hydraulics, affecting biologically important parameters such as water velocity and shear stress.

It disrupts the balance between sediment supply and transport, generally leading to increased sediment transport capacity and channel erosion.

It increases stream temperatures, due to the transfer of heat from impervious surfaces to stormwater runoff.

It increases delivery of pollutants from the landscape to the stream. Pollutants commonly found in stormwater runoff include:

  • sediment

  • nutrients
  • pesticides
  • wear metals
  • organic pollutants
  • oil and grease

Click below for more information on specific topics

effective vs. total imperviousness button imperviousness and biotic condition button thresholds of imperviousness button
Three common types of impervious surfaces in urban watersheds: roads, roofs, and parking lots.
Courtesy of U.S. EPA.
Figure 16. The shift in relative hydrologic flow in increasingly impervious watersheds. Note the large increase in stormwater runoff as imperviousness increases, at the expense of infiltration.
From Paul MJ & Meyer JL. 2001. The ecology of urban streams. Annual Review of Ecology & Systematics 32:333-365. © 2001 by Annual Reviews. Reprinted with permission.

Jump to main content.