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The NLCD [19] provides land-cover statistics that can be used as a qualitative measure of the prevalence of different land covers that may act as natural impervious areas. Open water may act as a natural impervious area if direct precipitation is routed through the channel network and arrives as stormflow at the site of interest.
As stormwater is channeled into storm drains and surface waters, the natural sediment load discharged to receiving waters decreases, but the water flow and velocity increases. In fact, the impervious cover in a typical city creates five times the runoff of a typical woodland of the same size. [9] [clarification needed]
Surface runoff (also known as overland flow or terrestrial runoff) is the unconfined flow of water over the ground surface, in contrast to channel runoff (or stream flow). It occurs when excess rainwater , stormwater , meltwater , or other sources, can no longer sufficiently rapidly infiltrate in the soil .
In hydraulic engineering, a nappe is a sheet or curtain of water that flows over a weir or dam. The upper and lower water surface have well-defined characteristics that are created by the crest of a dam or weir. [1] Both structures have different features that characterize how a nappe might flow through or over impervious concrete structures. [2]
Stormwater can soak into the soil and become groundwater, be stored on depressed land surface in ponds and puddles, evaporate back into the atmosphere, or contribute to surface runoff. Most runoff is conveyed directly as surface water to nearby streams, rivers or other large water bodies (wetlands, lakes and oceans) without treatment.
The total volume of water in rivers is estimated at 2,120 km 3 (510 cu mi), or 0.49% of the surface fresh water on Earth. [2] Rivers and basins are often compared not according to their static volume, but to their flow of water, or surface run off. The distribution of river runoff across the Earth's surface is very uneven.
Water that comes into contact with impervious surfaces, or saturated surfaces incapable of absorbing more water, is termed surface runoff. As the surface runoff travels greater distance over impervious surfaces it often becomes contaminated and collects an increasing amount of pollutants. A main challenge of stormwater harvesting is the removal ...
Cross section showing the water table varying with surface topography as well as a perched water table The vadose zone , also termed the unsaturated zone , is the part of Earth between the land surface and the top of the phreatic zone , the position at which the groundwater (the water in the soil's pores) is at atmospheric pressure ("vadose" is ...