The water cycle (also known as the hydrological cycle) describes the various states of water as it moves through the environment - falling as rainwater, infiltrating to groundwater, moving toward streams, evaporating to cloud systems, and so on.
As it moves through the environment, water interacts with
natural systems. Trees intercept rainfall, soil and humus layers attenuate stormwater
runoff and infiltrate it to ground, and terrestrial and aquatic vegetation captures and transpires water back to the atmosphere.
Land development disturbs these
natural processes through vegetation clearance and soil modification. The developed
site, with impervious surfaces and kerb and pipe systems, tends to bypass
natural systems and direct large stormwater volumes to lower catchment areas, resulting in flooding and potentially damaging effects to
natural stream and wetland environments.
A WSD approach to development protects and enhances existing '
natural' processes in the catchment. Where impervious surfaces do occur, stormwater
runoffis directed to vegetated landscapes and devices such as raingardens and swales, which mimic '
natural' processes through enhanced infiltration, transpiration and attenuation in floodplains.