Percentage imperviousness
Total impervious area
Natural impervious area
What does impervious material mean?
What are impervious surfaces? Impervious surfaces are any materials that do not allow water to flow through them. Examples include concrete, asphalt, and roofs.
What is meant by impervious soil?
Impervious soil means soil that has a minimum percolation rate slower than one inch in sixty minutes when the groundwater level is at least eighteen inches below the bottom of the percolation test hole.
Is Gravel considered impervious?
Gravel driveways are considered impervious because they prevent infiltration, which results in stormwater flowing off these surfaces at a higher rate than pervious surfaces. This is typically due to compaction of the underlying soil and stones by vehicles.
What is an example of a impervious surface?
An impervious surface is a hard surface that does not let water soak into the ground or greatly reduces the amount of water that soaks into the ground. Examples include: roofs. solid decks. patios.
What are impervious surfaces?
Impervious surfaces are mainly artificial structures—s uch as pavements ( roads, sidewalks, driveways and parking lots, as well as industrial areas such as airports, ports and logistics and distribution centres, all of which use considerable paved areas) that are covered by water-resistant materials such as asphalt, concrete, brick, stone —and rooftops. Soils compacted by urban development are also highly impervious.
How much does impervious cover increase?
In rural areas, impervious cover may only be one or two percent. In residential areas, coverage increases from about 10 percent in low-density subdivisions to over 50 percent in multi-family communities. In industrial and commercial areas, coverage rises above 70 percent.
Why do pervious areas behave like impervious areas?
Developed pervious areas may behave like impervious areas because development and subsequent use tends to compact soils and reduce infiltration rates. For example, Felton and Lull (1963) measured infiltration rates for forest soils and lawns to indicate a potential 80 percent reduction in infiltration as a result of development activities. Similarly, Taylor (1982) did infiltrometer tests in areas before and after suburban development and noted that topsoil alteration and compaction by construction activities reduced infiltration rates by more than 77 percent.
What percent of the US is impervious?
Homer and others (2007) indicate that about 76 percent of the conterminous United States is classified as having less than 1 percent impervious cover, 11 percent with impervious cover of 1 to 10 percent, 4 percent with an estimated impervious cover of 11 to 20 percent, 4.4 percent with an estimated impervious cover of 21 to 40 percent, and about 4.4 percent with an estimated impervious cover greater than 40 percent.
Why are impervious surfaces considered environmental?
Impervious surfaces are an environmental concern because their construction initiates a chain of events that modifies urban air and water resources: The pavement materials seal the soil surface, eliminating rainwater infiltration and natural groundwater recharge. An article in the Seattle Times states ...
Why are wetland areas considered impervious?
Barren ground in riparian areas may act as a natural impervious area during storms because these areas are a source of infiltration excess overland flows .
How much is urban impervious cover?
In the contiguous 48 states of the US, urban impervious cover adds up to 43,000 square miles (110,000 km 2 ). Development adds 390 square miles (1,000 km 2) annually. Typically, two-thirds of the cover is pavements and one-third is building roofs.
What is impervious layer?
Impervious layer or material is characterized as having a percolation rate slower than one hundred twenty (120) minutes per inch or having clay content of sixty (60) percent or greater.
What is a pervious surface?
Pervious surface means an area that releases as runoff a small portion of the precipitation that falls on it. Lawns, gardens, parks, forests or other similar vegetated areas are examples of surfaces that typically are pervious.
What is the thickness of an impervious layer?
Impervious layer — constant thickness, varying from 5 to 10 cm.; 6 to 8 percent asphalt; densely graded aggregate; high compaction to about 3 percent air voids content; and impermeable.
What is the floodplain in ARM?
The floodplain consists of the floodway and the flood fringe, as defined in ARM Title 36, chapter 15. (11) through (13) remain the same. (14) " Impervious layer " means any layer of material in the soil profile that has a percolation rate slower than 120 240 minutes per inch.
Overview
The Impervious Surface raster layer represents impervious surfaces covering the Commonwealth of Massachusetts. The surfaces were extracted using semi-automated techniques by Sanborn Map Company from 50-cm Vexcel UltraCam near infrared orthoimagery that was acquired in April 2005 as part of the A erial Imagery project.
Production
A standard semi-automated methodology for extraction of impervious surfaces was developed and adopted. A hybrid classification method was used to extract impervious/pervious features. The primary software tools used were Definiens eCognition and Leica ERDAS Imagine. MassGIS then added a rasterized EOT Roads dataset.
What MassGIS distributes
Because the entire statewide dataset totals almost 4.5 GB in size, MassGIS has chosen to tile the data for easier distribution and file handling. The data, in Erdas Imagine (.img) file format, have been broken up into 33 pieces based on the 2005 Color Ortho Mosaic Index.
What is impervious fill?
Impervious fill helps to prevent large amounts of water from running down behind the wall or getting to the leveling pad. Generally, compacted fine grained soil is used as impervious fill.
Why is it important to compact foundation and backfill soils?
It is important to compact foundation and backfill soils to prevent future wall movement. Compaction is often accomplished using a hand tamper or a vibratory-plate compactor (available at most rental stores). Course. A horizontal layer of retaining wall units.
How tall is a gravity wall?
A retaining wall without soil reinforcement where unit weight alone provides resistance to earth pressures. Gravity walls are generally less than four feet in height and do not support slopes or other loads above the walls.
Why are canted walls more stable than vertical walls?
Canted walls are structurally more stable than vertical walls because gravitational forces "pull" walls into retained soil. Soil Reinforcement.
How does a Versa Lifter work?
The VERSA-Lifter speeds installation of VERSA-LOK retaining walls by making it easier to lift and place units — especially on the base course. The two prongs of the lifter are inserted into pin holes in the VERSA-LOK unit. The action of lifting the handle secures the lifter to the unit and makes for easy, balanced lifting and placement.
Overview
Impervious surfaces are mainly artificial structures—such as pavements (roads, sidewalks, driveways and parking lots, as well as industrial areas such as airports, ports and logistics and distribution centres, all of which use considerable paved areas) that are covered by water-resistant materials such as asphalt, concrete, brick, stone—and rooftops. Soils compacted by urban development are also hig…
Environmental effects
Impervious surfaces are an environmental concern because their construction initiates a chain of events that modifies urban air and water resources:
• The pavement materials seal the soil surface, eliminating rainwater infiltration and natural groundwater recharge. An article in the Seattle Times states that "while urban areas cover only 3 percent of the U.S., it is estimated that their runoff is the primary source of pollution in 13 percen…
Mitigation of environmental impacts
Impervious surface coverage can be limited by restricting land use density (such as a number of homes per acre in a subdivision), but this approach causes land elsewhere (outside the subdivision) to be developed, to accommodate the growing population. (See urban sprawl.) Alternatively, urban structures can be built differently to make them function more like naturally pervious soils; exam…
Percentage imperviousness
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. An estimation of PIMP is given by PIMP = 6.4J^0.5 where J is the number of dwellings per hectare (B…
Total impervious area
The total impervious area (TIA), commonly referred to as impervious cover (IC) in calculations, can be expressed as a fraction (from zero to one) or a percentage. There are many methods for estimating TIA, including the use of the National Land Cover Data Set (NLCD) with a Geographic information system (GIS), land-use categories with categorical TIA estimates, a generalized percent developed area, and relations between population density and TIA.
Natural impervious area
Natural impervious areas are defined herein as land covers that can contribute a substantial amount of stormflow during small and large storms, but commonly are classified as pervious areas. These areas are not commonly considered as an important source of stormflow in most highway and urban runoff-quality studies, but may produce a substantial amount of stormflow. These natural impervious areas may include open water, wetlands, rock outcrops, barren ground …
See also
• Bioswale
• Hardscape
• Hydraulic conductivity
• Hydrophobic soil
• Permeability (fluid)
Bibliography
• Butler, D. and Davies, J.W., 2000, Urban Drainage, London: Spon.
• Ferguson, Bruce K., 2005, Porous Pavements, Boca Raton: CRC Press.
• Frazer, Lance, 2005, Paving Paradise: The Peril of Impervious Surfaces, Environmental Health Perspectives, Vol. 113, No. 7, pg. A457-A462.