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Impervious surface percentage in various cities. The percentage imperviousness, commonly referred to as PIMP in calculations, is an important factor when considering drainage of water. It is calculated by measuring the percentage of a catchment area which is made up of impervious surfaces such as roads, roofs and other paved surfaces.
Flooded streets in New Orleans Relationship between impervious surfaces and surface runoff Urban runoff is a major cause of urban flooding , the inundation of land or property in a built-up environment caused by rainfall overwhelming the capacity of drainage systems , such as storm sewers . [ 12 ]
Surface runoff often occurs because impervious areas (such as roofs and pavement) do not allow water to soak into the ground. Furthermore, runoff can occur either through natural or human-made processes. [5] Surface runoff is a major component of the water cycle. It is the primary agent of soil erosion by water.
The street has 11% less impervious surface than a regular street. There are 100 evergreen trees and 1100 shrubs along this 3-block stretch of road, and a 2-year study found that the amount of stormwater which leaves the street has been reduced by 99%. [38] 10,000 Rain Gardens is a public initiative in the Kansas City, Missouri metro area ...
Any activities that enlarge the impermeable surface areas in a city can increase the flood risk. Impermeable surface areas are generated through soil sealing as this reduces drainage options of floodwaters. [3]: 925 As the pace of urbanization accelerates around the world, urban flooding has the potential to affect more people. [3]: 925
For example, sheer vertical features are possible. Without nearby bare soil, or natural drainage channels, swales or culverts, hardscape with an impervious surface requires artificial methods of drainage or surface runoff to carry off the water that would normally be absorbed into the ground as groundwater and prevent premature wear to itself.
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 ...
Storm drain grate on a street in Warsaw, Poland Storm drain with its pipe visible beneath it due to construction work. A storm drain, storm sewer (United Kingdom, U.S. and Canada), highway drain, [1] surface water drain/sewer (United Kingdom), or stormwater drain (Australia and New Zealand) is infrastructure designed to drain excess rain and ground water from impervious surfaces such as paved ...