Pervious Pavements

From Swikipedia

Introduction

Pervious pavement is designed to allow percolation or infiltration of storm-water through the surface into the soil below where the water is naturally filtered and pollutants are removed. In contrast normal pavement is an impervious surface that sheds rainfall and associated surface pollutants forcing the water to run off paved surfaces directly into nearby storm drains and then into streams and lakes.

Brief Description

There are numerous types of pervious surfaces that can be divided into two categories:

1. Porous Surfaces

2. Permeable Surfaces

Porous surfaces are made up of a material that is itself pervious, while permeable surfaces are made up of impervious material that leaves spaces for water to flow through. Both work by allowing water to flow through the surface into the supporting sub-base, which either works to sift out impurities and allow the water to filter into the soil over a period of time or filters and slows the flow rate of water, while also directing it to another part of the drainage system. Often a combination of these techniques is used: if the rainfall is light enough, the soil can handle the water and all the water is dispersed into the ground, but if the flow gets too heavy, the ground can not hold it and some is directed to other parts of the drainage system.

Benefits of Pervious Pavements:

 Reduce storm water runoff. (Even when pervious pavement structure is saturated, its rough surface texture continues to slow surface flow of storm water)

 Replenish groundwater

 Reduce flooding which may over-load combined sewer sewage treatment plants

 Require less land set aside and cost for development of retention basins

 Reduce pollutants in run-off

 Reduce irrigation of area plantings based on the seepage of rain into the sub soil surfaces

 Reduce thermal pollution

 Lessen evaporative emissions from parked cars

 Reduce glare and automobile hydroplaning (skidding) accidents

Construction Considerations:

 Permeable surfaces can be laid without cross-falls or longitudinal gradients

 The blocks should be lain level

 They should not be used for storage of site materials, unless the surface is well protected from deposition of silt and other spillages.

 The pavement should be constructed in a single operation, as one of the last items to be built, on a development site. Landscape development should be completed before pavement construction to avoid contamination by silt or soil from this source.

 Surfaces draining to the pavement should be stabilized before construction of the pavement.

 Inappropriate construction equipment should be kept away from the pavement to prevent damage to the surface, sub-base or sub-grade.

References:

The Energy and Resources Institute. Sustainable Building Design Manual, Volume 2. p.p 32.

http://www.duluthstreams.org/stormwater/toolkit/paving.html

http://www.cabmphandbooks.com/Documents/Development/SD-20.pdf