Understanding Your Neighborhood's
Drainage System
Neighborhood stormwater systems are often "out of sight, out of
mind," but the systems play a key role in preventing flooding,
pollution and erosion.
Facilities in Older
Housing Developments
Runoff is usually sent directly into rivers and streams
If you live in an
older housing development -- built in the early 80s or earlier -- chances
are the stormwater runoff from your area flows through a storm drain (a
street grate) and into a catch basin (a tank below a storm drain). The
storm drains and catch basins are often located on roads within the
subdivision.
When water enters
the catch basin, polluted sediments settle to the bottom of the tank. Once
the water reaches a certain level in the tank, the upper layers flow
through an outlet pipe and directly into the nearest stream, lake or bay.
(Some older neighborhoods use "drywells," which are catch basins with open
bottoms and perforated sides that allow water to infiltrate directly into
the ground.)
Facilities in Newer Housing
Developments
Runoff is usually sent to a stormwater pond first
If
you live in a newer development, stormwater runoff usually flows into a
storm drain/catch basin or along a shallow ditch or swale. But unlike older developments, most newer developments send
water into a stormwater pond. (Click here
for a PDF on how to maintain your stormwater pond.)
There are two kinds
of ponds:
- Wet pond: A wet
pond has a clay-like bottom or synthetic-fabric liner that keeps the
water from seeping into the ground. This allows the sediments more time
to sink to the bottom of the pond. An overflow pipe carries the cleaner
water on top to a nearby water body (or, sometimes, to a dry pond). A
wet pond usually has cattails and other aquatic plants growing in it
which help remove pollutants. (Wet ponds are sometimes referred to as
"detention ponds" or "artificial wetlands.")
- Dry pond: The
second type of pond, a dry pond, has sandy soil on the bottom and allows
stormwater to seep into the ground. Dry ponds, also called infiltration
ponds, are usually seeded with grass and are sometimes used for
recreational purposes in the summer when there is no water in them. Some
newer developments have a dual pond system: a wet pond for cleaning the
water, and a dry pond for infiltrating the cleaned water back into the
ground. (Dry ponds are sometimes referred to as "retention ponds.")
Some apartment
complexes may have larger tanks, or vaults, under the parking lot. These
larger vaults may have water-quality treatment features like oil/water
separators or compost filters. If you have this type of facility, you
should already possess maintenance information from the developer who
installed the facility, or from the manufacturer of the facility. If not,
call the Thurston County Storm and Surface Water Utility at (360)
754-4681, for assistance.
