Urban stormwater basin assessment
Introduction
Impervious surfaces are primarily man-made structures such as pavements (roads, sidewalks, driveways and parking lots, as well as industrial areas such as airports, ports, and logistics and distribution centers) that are covered by water-resistant materials such as asphalt, concrete, brick, stone and roofs "Roof (construction)"). Soils compacted by urban development are also highly impermeable.
Environmental effects
Impermeable surfaces have effects on the environment because their installation starts a chain of events that modifies the air in cities and water resources:
• - Impervious surface materials prevent water from passing into the soil, eliminating rainwater infiltration and natural groundwater recharge. This can cause urban flooding. A Seattle Times article states that “although urban areas cover only 3 percent of the U.S., their runoff is estimated to be the primary source of pollution in 13 percent of rivers, 18 percent of lakes and 32 percent of estuaries.”
• - Impermeable surfaces capture the sun's energy and use it to heat themselves (a plant surface partially uses solar energy for the growth of its plants, so it heats up less). When released, this heat raises the air temperature, generating urban "heat islands" and increasing energy consumption in buildings (due to air conditioning). When rain falls on these hot surfaces, the oxygen carried by rainwater decreases (the amount of gas that can be dissolved in a liquid decreases as the temperature of that liquid increases), and warm runoff reduces the oxygen dissolved in the water of rivers and streams, making life in aquatic ecosystems more difficult.
• - Impervious pavements deprive tree roots of aeration, eliminating the “urban forest” and the shade of their canopies that would otherwise temper the urban climate. Because impervious surfaces displace living vegetation, they reduce ecological productivity ('Productivity (ecology)') and disrupt the atmospheric carbon cycle.
The impervious surface coverage of an area, such as a municipality or a watershed, is generally expressed as a percentage of the total surface area. This coverage increases with the urbanization process. In rural areas, impervious coverage may be only 1 or 2 percent. In residential areas, coverage increases from about 10 percent in low-density subdivisions to more than 50 percent in multifamily communities. In industrial and commercial areas, coverage exceeds 70 percent. In regional shopping centers and dense urban areas, this figure exceeds 90 percent. In the contiguous 48 US states, urban impervious coverage totals 43,000 square miles (111,370 km²). The development adds 390 square miles (1,010.1 km²) annually. Normally, 2 thirds of this impervious surface are pavements and the remaining third is made up of building roofs.