As stated earlier, current building practices result in large amounts of any building
lot being covered with impervious surfaces such as asphalt, concrete and the house
or commercial building itself with its metal, shingle, or membrane roof.
According to Environmental Health Perspectives, reprinted on-line by the National
Institute of Health, as much as 10 percent of a two acre home site and 65 percent
of a 1/8 acre lot will probably be covered with some sort of "paved"
On a community level, local authorities must be encouraged to cut back on the
width of streets required in new subdivisions. Many communities insist that
builders put in paved streets that are thirty to forty feet wide even in subdivisions
with little traffic, a practice described as "insane" by Robert Bannerman, a
researcher with the Department of Natural Resources for the State of Wisconsin.
He maintains that 25 to 28 foot widths are adequate. Citizens could make a difference
by checking out local subdivision regulations and lobbying for change where
Beyond the size of the paved area is the composition of the materials. There
are many alternatives to the impervious materials typically used in residential
Porous concretes and asphalts provide solid surfaces for foot and vehicle traffic
but allow rainwater to seep down into subsurface soils. These porous materials
are made with a lower concentration of fine aggregate in the coating and can
be mixed at a regular asphalt plant. This porous material is laid over a bed
composed of the uniformly sized aggregate materials which minimize voids and
allow water to filter through. Under this layer is a special fabric layer which
allows water to filter down but prevents soil from moving upward where it could
penetrate and clog the aggregate. Such material is suitable for use on both
streets and driveways and could be required by local building code.
Individual homeowners can increase the porosity of driveways and sidewalks
by using any number of other materials other than concrete or asphalt; crushed
shells and wood mulch are popular. Areas, such as auxiliary parking, that do
not receive a lot of vehicular traffic can be planted with a hearty turf.
Increasingly popular are pavers with open joints that can
be filled with aggregate or turf. Laying pavers is labor intensive but results
in a very handsome finish and now there is a method available that allows concrete
to be poured into a grid and finished to look like stone. When the grid is removed
it leaves open spaces that can be filled with aggregate or planted with turf.
In order to most effectively control runoff, pavers must be installed over
a multi-layered aggregate system, but even if laid directly on gravel without
any special preparation, pavers will reduce runoff by some 20 percent.
Another major source of water loss to runoff is the roof of a house or a commercial
building. Here a catchment system can substantially reduce this loss and its
potential contribution to flooding.
The simplest rainwater catchment system is composed of a container
to catch and store rainwater coming from a downspout before it has a chance
to run into a driveway, sidewalk, or the street. The container can be anything
from a new 20 gallon trash can to an above ground or buried cistern made of
metal, wood, plastic, concrete, or other materials. A cistern measuring six
feet high by six feet in diameter can hold an impressive 1,269 gallons of water.
In a commercial development a 20 x 18 foot container will store over 38.000
gallons of water for reuse and keep that amount from adding to the runoff already
pouring from roads and parking lots.
Note: It is important to provide a lid on any type of storage container and
to screen downspouts leading from the roof to prevent the breeding of mosquitoes
in the stored water.
At its most rudimentary level this saved water can irrigate planting beds using
gravity feed or a simple pump such as a submersible sump pump attached to a
garden hose. It is estimated that the typical home may dedicate as much as 40
percent of its water usage to lawn and garden irrigation so
any amount of water collected and reused will lessen pressure on the well or
lower municipal water bills.
In rural areas, where annual rainfall is sufficient and consistent to justify
what is a large initial expense, roof collection systems can be engineered to
provide the water needs for an entire household including drinking and sanitary
water. Installation of such systems is not initially cost-competitive with hooking
up to city water service but may be comparable to the cost of drilling a well.
Total water service systems require first-flush diverters that allow the early
part of a downpour to remove dust, leaves, bird droppings and so forth from
the roof, diverting that water to outdoor irrigation. Systems may also require
roof washers, filters, and various kinds of water treatment systems.
Above and beyond conserving water, mitigating runoff, and saving on household
utility bills, rainwater is typically much softer than water coming
from city systems or from local wells. This lack of "hardness" means that less
soap and detergent is needed to wash clothes, dishes, and people. Using water
that is relatively free of the mineral deposits that make water "hard" will
also increase the life of appliances such as washers and dishwashers and reduce
the cleaning and cleaning products necessary to keep toilets, showers, and tubs
Rainwater, having not traveled down driveways and streets, into rivers and
streams, and then into city surface or groundwater supplies, is free of many
contaminants such as fecal coli form bacteria, industrial chemicals,
and pesticides. Because it doesn't have to be treated, pumped, or distributed
back to the home from whence it came, it saves energy and the use of treatment
chemicals such as chlorine. Another benefit; garden plants expect rainwater
not the stuff that comes from city pipes, and thrive when they get it.
According to Mother Earth News, "a state-of-the art rainwater harvesting system
for a typical family and containing sophisticated filtering and purification
components can cost $15,000 to $20,000". Rainwater harvesting systems
costs depend on whether an appropriate roof surface already exists,
how big and what kind of cistern is used and what level of filtration and purity
is required. Some state and local governments provide tax incentives
to property owners who install some types of rainwater recycling systems.
And, of course, we all know that there is nothing new under the sun, and so
we have the rediscovery of the "green roof." Green roofs date
back hundreds of years but began to emerge in alternative construction about
30 years ago in Germany. Today there are green roofs, mostly on commercial or
large scale residential buildings throughout the world and the concept is becoming
increasingly attractive as an environmentally terrific installation for individual
homeowners. Because green roofs have applications and benefits well beyond,
but certainly including inhibiting runoff and recycling water, we will describe
them in later articles dealing with energy conservation.