| aeration |
A process whereby air voids are introduced into soil for improved
fertility and water holding capability. |
| bio-remediate |
Bio-remediation uses biological processes to repair pollution
damage. For example, a grass swale can bio-remediate much of the
pollution caused by automobile use by holding heavy metals in the
soil at harmless concentrations as well as by the action of soil
bacteria, which gradually breaks down hydrocarbon waste such as
crankcase oil. |
| bollard |
A sturdy element, usually a post, placed in such a way as to prevent
automobiles from entering an area. |
| catchment planter |
A planting bed that has been specially designed to hold and absorb
storm flows from adjacent areas, usually from parking lots. |
| cistern |
Any tank or recess used to capture and store rain water for later
use. |
| drainage chimney |
Holes drilled into the ground sufficiently deep to allow rain
water to quickly flow back into the ground. |
| drainage flow deflector |
A ridge and/or a depression in a flat paved surface for the purpose
of re-directing sheet flow into a channel, thus changing the destination
of storm water. |
| dry flow |
The continuous flow in a storm drain system that occurs even during
extended periods without rain. |
| evapotranspiration |
The loss of water from the soil both by evaporation and by transpiration
from the plants growing thereon. |
| filter medium |
Any item or substance that is used for filtering impurities. In
many of the designs included in this planbook, soil, sand, and mulch
were used as a filter medium. |
| first-flush rain |
In the Los Angeles area, many months can pass between one rain
storm and the next. During this time, pollution and grime build
up on all of the city's outdoor surfaces, and in particular, on
its streets. When the next rain storm finally comes, it washes the
accumulated grime and pollution off of the streets and into the
underground storm drain system. This is the "first flush rain."
As you might expect, it carries a very large amount of suspended
and dissolved pollutants. |
| gabion wall |
A sloping wall used mostly to line streams made of rock filled
wire cages. |
| grass filter strips |
A grassy edge or swale which filters storm water in the root layer
before percolating the water into the soil below or discharging
the water overland. |
| graywater |
Water drained from household sinks, washers, tubs, and showers
- that is, all water not coming from toilets. This water carries
relatively few suspended or dissolved solids. Consequently, it can
often be used for such purposes as landscape irrigation. |
| green filter islands |
A grassy or planted landscaped island, usually in a parking lot,
that filters storm water in the root layer before percolating the
water into the soil below or discharging the water overland. |
| green link |
Green links connect various locations via generous planted "park
like" linear corridors. |
| groundwater |
Groundwater is water that saturates the soil at some distance
below the surface. The level of groundwater or "water table" varies
from soil to soil and from season to season. In rare instances,
and on particular sites, the groundwater table comes up to the surface.
This results in standing water on the surface of the ground. More
often, the groundwater table is located many feet below the surface.
|
| groundwater mounding |
In certain instances, where stormwater is returned to the soil
in one location at a faster rate than in adjacent locations, groundwater
mounding can occur. This means that the water table (where the soil
is saturated) can be higher under a recharge basin than in adjacent
locations. Occasionally this can create problems. Often it is benign.
|
| growing medium |
Any substance used to plant plants in. This is almost always soil.
Sometimes soil will be substantially amended with additives, fertilizers,
and organic material. Substantially amended soil is commonly referred
to as growing medium. |
| heat gain |
Heat can slowly build up in an object over time. This is called
heat gain. In a building heat gain is most often the consequence
of many hours of sunshine striking and warming the exterior walls
and roof. |
| heat island effect |
Many urban areas lack shade trees. In these areas the sun strikes
pavement and rooftops, heating them to very high temperatures. These
surfaces re-radiate heat back into the air, raising air temperatures
by five or more degrees. Urban areas that contain dense tree canopy
avoid the heat island effect because trees absorb virtually all
of the sun's energy without radiating heat back into the air. |
| high crowns |
Virtually all roads and parking areas have some kind of crown,
or high point, to insure that water flows off promptly. Usually
this high point is a ridge along the center line of the road or
parking bay. This ridge is ordinarily only a few inches higher than
the edges. "High crown" suggests a condition where this crown is
made artificially higher to allow the road or bay to hold more water
than it otherwise could. |
| holding pond |
A depression where rain water is directed and held temporarily.
Holding ponds function to slow the rate at which water is discharged
from a site to the rate more typical of undeveloped natural sites.
|
| humus layer |
The top layer of soil where there is the most organic activity,
fibrous root material, and recycling detritus from the plants above.
|
| hybrid cistern system |
A container for holding rain water, both as a resource for later
use and to help alleviate downstream flooding during time of flood
threat. |
| infiltration zone |
An area patricularly well suited and/or altered for directing
storm water back into the soil. |
| impervious pavement |
No water can penetrate through an impervious pavement. Almost
all asphalt and concrete pavement is impervious. |
| percolation rate |
The rate at which water can filter into the soil. Some soil types,
such as sand, have a very high percolation rate; other soils types,
such as clay, have a very slow percolation rate. |
| permeable pavement |
Permeable pavement is honey-combed with voids, or air-pockets.
These voids allow water to migrate down through the pavement into
the soil below. |
| potable water |
Water that is fit to drink. |
| recharge areas |
Certain zones in the landscape can accept water back into the
soil at higher than average rates. Such areas are often referred
to as recharge areas. |
| residential density |
The number of family units to be found on an average acre of land
in a residential area is referred to as its density. These densities
range from low (1-2 units per acre) to high (40 + units per acre).
|
| riparian retention and treatment area |
A retention or recharge area where plants native to rivers or
lakes are installed to consume and clean the water therein. |
| run off |
Stormwater that flows off of one surface or site onto another. |
| shade trees |
Trees large enough to shade a two-story building. In some climates,
shade trees lose their leaves in the winter. Some evergreen trees
are suitable shade trees, but they may shade the house or street
during the winter when people would prefer to have the light and
warmth of the sun. |
| sheet flow |
Sheet flow is storm water that flows in even sheets across a flat
surface, such as a parking lot. |
| soaker hose |
Soaker hoses are water conserving means of watering shrub beds
especially. These hoses contain small perforations that allow water
to flow gradually and continually onto the soil. They work particularly
well with cisterns as they operate well with the low water preasures
typically delivered by cisterns. |
| stormwater |
Stormwater refers to all rain water that hits the surface of the
ground. Stormwater either percolates back into the soil or flows
on the surface to the nearest storm drain inlet, stream, or other
wetland area. |
| subsoil |
The soil layer below the "topsoil" layer. |
| subsurface |
Below the surface of the ground. |
| swale |
A v-shaped depression in the land, usually lined with grass, designed
as a channel for moving storm water from one place to another. |
| trellis |
A small structure, usually made of wood, wire, or metal, designed
to support plants such as twining vines. |
| watershed |
A region or area bound peripherally by a water parting or ridge
and draining ultimately to a particular watercourse or body of water.
Most sites are now mini watersheds, with the property line constituting
the "ridge" and the storm drain system located in the street constituting
the "watercourse" to which it discharges. |
