Great Lakes Communities and Ecosystems
Water Cycle How the cycle works Added human pressures

SURFACE & SUBSURFACE RUNOFF
Water flows from areas where the water table is higher to areas where it is lower. This flow can be either surface runoff in rivers and streams, or subsurface runoff infiltrating rocks and soil. The amount of runoff reaching surface and groundwater can vary significantly, depending on rainfall, soil moisture, groundwater storage, evaporation, upstream use, and whether or not the ground is frozen. The movement of subsurface waters is determined largely by the water gradient, type of substrate, and any barriers to flow.

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Water Cycle diagram

© 2003 Union of Concerned Scientists Riparian ZonesGreat LakeWetlandsGroundwaterForestsSurface and Subsurface RunoffSurface WaterInfiltrationEvaporationWatershed BoundaryTranspirationPrecipitationCondensation