For General Public Works FAQs
What is Stormwater?
Stormwater is rain, snow or sleet that is a direct result of
precipitation. It flows in concentrated forms (pipes, gutters, ditches, streams,
etc.) and diffuse forms (sheet flow) over or within all land forms. Stormwater
soaks into the soil and becomes ground water, is used by vegetation, evaporates,
or flows into lakes or streams as surface flow. Stormwater collects pollutants
and debris as it travels down to our local waterways. For more information visit
our What is Stormwater page.
What is a watershed and how do I know in which
watershed I am located?
A watershed, also called a drainage basin, is the area of land where all
of the water within it drains to the same place. John Wesley Powell, scientist
geographer, put it best when he said that a watershed is: "that area of land, a
bounded hydrologic system, within which all living things are inextricably
linked by their common water course and where, as humans settled, simple logic
demanded that they become part of a community." Watersheds come in all shapes
and sizes. They cross county, state, and national boundaries. No matter where
you are, you're in a watershed! More information is available at
www.epa.gov/watershed/.
The City of Redmond is divided into 68 small watersheds that drain to
Lake Sammamish, the Sammamish River, or directly to Lake Washington. A
map of those watersheds is available on the City’s
GIS
Maps page. All of these watersheds lie within the Sammamish
Watershed which is in turn a part of the WRIA-8 Cedar-Sammamish
Watershed which is described in more detail at
www.ecy.wa.gov/programs/eap/wrias/08.html.
Why do we need to manage stormwater?
Urbanization causes significant changes in stormwater runoff
characteristics. As the natural landscape is cleared, graded, and covered with
buildings and parking lots, rainwater can no longer filter into the soil to
become groundwater. As a result, more rainwater enters our lakes and streams,
and it enters more quickly. As it flows across parking lots, streets, and hard
surfaces, it picks up pollutants and debris and carries them to the lakes and
stream along with the water. This increased volume and rate of run-off increases
erosion and formation of gullies in upland areas, increases scour and erosion in
streams, increases sediment deposition in lower areas, degrades water quality,
causes more frequent flooding, and negatively effects stream ecology. These
impacts on both man-made and natural systems require continuous management,
maintenance, repair and replacement and careful planning to mitigate existing
and future problems.
Federal law requires that Redmond participate in activities to manage
stormwater as part of the NPDES program.
What is NPDES?
NPDES stands for National Pollutant Discharge Elimination System, which
is a regulation of the federal Clean Water Act. NPDES requires that all
stormwater discharges that enter waters of the United States meet minimum
federal water quality standards. This is accomplished through an NPDES permit.
The goal of NPDES permitting is to improve and protect the quality of our
nation's waterways by eliminating pollution from stormwater runoff to the
maximum extent practicable.
What is considered to be an impervious surface?
An impervious surface is any surface that prevents water from soaking
into the ground. Examples include roofs, driveways, parking lots, swimming
pools, patios, paved areas, tanks, pads, and other features that are impermeable
to rainfall.
What is a catch basin?
A catch basin is a concrete box that is typically connected to a pipe
system or open channel. Water enters the catch basin through a grated opening in
the top and is eventually carried to a stream, river, lake, or groundwater. A
catch basin is typically located in the street, on the curb or in a yard A catch
basin typically has a “sump” in the bottom. The purpose of this sump is to allow
sand, gravel, and sediment to settle out instead of being carried to the stream
or lake. Routinely, the sediment and sand must be cleaned out.
Do catch basins and storm drains get cleaned out?
Yes, the City of Redmond's Stormwater
Maintenance Operations Center (MOC) cleans catch basins and storm drains as needed.
The City also inspects
private systems to make
sure they are maintained and operating properly.
Why doesn't the City of Redmond install filters or
screens in front of catch basins?
Installing a filter or screen in front of a catch basin is not a
practical solution to curbing the amount and type of pollution entering the
storm sewer system. They are hard (labor-intensive) to maintain and can cause
street flooding when they clog up with leaves and other debris.
Why doesn't the City of Redmond build a stormwater
treatment plant?
The variation in rainfall amounts and runoff volume would make a stormwater treatment plant economically infeasible. Rainfall not only falls in
varying amounts, but also falls in varying quantities from one side of the City
of Redmond to the other. In many storm events runoff volumes can be excessive.
In particular, in developed areas small rainfall events can generate large
amounts of runoff. We also have hundreds of outfalls to miles of streams.
What is the City of Redmond doing about illegal
dumping into the storm drains?
There is an ordinance that prohibits dumping and litter. Enforcement of
this ordinance is part of the City of Redmond’s NPDES permit requirements. Code
enforcement officers are authorized to cite any person or persons caught
illegally dumping any material other than rainwater into a storm drain.
What is a stormwater pond?
When rainwater lands on rooftops, streets, driveways and other impervious
surfaces, the runoff flows into the storm drains around your neighborhood. In
most developments, pipes and ditches carry the water into a nearby stormwater
pond. Stormwater ponds are manmade depressions in the land that store rainwater
until it can drain into the ground water -- our source of drinking water -- or
slowly release it into streams, lakes, wetlands, or the river.
Stormwater ponds help prevent flooding. They also protect rivers,
streams, lakes and ground water. Stormwater runoff carries litter, oil,
gasoline, fertilizers, pesticides, pet wastes, sediments and anything
else that can float, dissolve or be swept away by moving water.
Stormwater ponds serve as a filter, screening out some of these
pollutants before they enter our ground water aquifer, lakes or
streams..
A stormwater pond in your neighborhood might be located in your back
yard or, if you live in a housing development, down the street or on
nearby property. The City constructs and maintains large regional
stormwater ponds to manage stormwater from larger portions of the City.
Isn't a stormwater pond supposed to have standing water in it?
Not always. In fact, many stormwater ponds are designed to go dry within
a certain period, typically two to six days. These "dry" ponds often look like
shallow bowls in the land. The ponds store stormwater and gradually allow it to
filter into the ground. That's why dry ponds are usually located in areas that
have porous or sandy soil.
"Wet" ponds are often lined with plastic or clay to prevent water
from infiltrating into the ground, and they have water in them most of
the time. When the water in a wet pond reaches a certain level, it
typically flows through a pipe, much like the overflow drain in a sink.
The pipe sends the water either to a dry pond to soak into the ground,
or into the nearest lake, river, stream, or other "surface" water body.
Dry ponds and wet ponds differ in their treatment of polluted
stormwater. Dry ponds are not designed to treat water, but rather, to
get rid of it. By contrast, wet ponds treat polluted stormwater by
allowing sediment to settle out before the water is released.
Wetland-type plants in the pond also help remove impurities. Sometimes
an underground vault or pipe is used to store and treat stormwater,
instead of a pond. Detention vaults and pipes are usually located
beneath the street and parking lots. Most of Redmond's ponds are wet
ponds, lined to protect our
groundwater aquifer.
The ponds share two features in common: Both are designed to help
prevent flooding and to protect streams and lakes from receiving high
volumes of fast, polluted runoff during storms.
Why do we need to maintain our stormwater pond?
Flooding, pollution, soil erosion, and destruction of wildlife habitat
may result from poorly maintained stormwater ponds. Ponds that are choked by
yard debris or overgrowth can cause water to spill onto adjacent property.
Additionally, ponds that send water too quickly into streams and rivers can
worsen soil erosion along the banks, harming wildlife habitat. Ponds that are
not maintained properly do not adequately filter pollutants from the stormwater
before releasing it to streams, lakes, and wetlands.
Letting your stormwater pond fall into disrepair can also cause
damage to your wallet. Small problems escalate into large repair bills,
and other property owners can take you to court to repair flood damage.
Also, the entire community bears the cost when valuable aquatic habitats
are damaged or destroyed. This damage often cannot be reversed.
Who is responsible for maintenance?
Businesses, individuals or homeowner's associations are responsible for
regularly maintaining privately owned ponds, pipes, ditches, swales and other
drainage systems. Local governments take care of stormwater facilities that are
located in public right-of-ways or on public property. If you are unsure of who
is maintaining a facility, contact the City’s Drainage System Inspection Program
at 425-556-2825 or
nr@redmond.gov. More information is available at
the
Drainage Inspection Program page.
What stormwater facilities are potential breeding
grounds for mosquitoes that carry West Nile Virus?
Catch Basins
Mosquitoes that carry the West Nile virus can breed in standing
water. Many of the catch basins in Redmond are designed to trap
pollution and hold a small amount of stormwater after a rainfall event.
These catch basins can be breeding grounds for mosquitoes that carry
West Nile virus.
Stormwater Ponds and Water Quality Facilities
Stormwater ponds and water quality facilities are designed to filter
pollution from stormwater runoff and reduce flooding. Most of the
facilities built into residential and commercial developments since 1990
are designed to drain in a few days, which prevents mosquito larvae from
completing their development.
Some stormwater ponds and water quality facilities are designed to
hold water most of the year or may retain small pools of water. These
facilities are generally designed to provide habitat for many species of
frogs, birds, fish and aquatic insects that feed on mosquitoes and their
larvae. The City of Redmond will evaluate the maintenance of these
facilities to reduce mosquito-breeding habitat and improve the habitat
for natural mosquito predators.
Wetlands
Although healthy wetlands can provide habitat for mosquitoes, typical
water conditions, water quality, and natural predators deter mosquito
use and minimize larval success if egg laying occurs. Predators -
including other aquatic insects, amphibians, and birds - feed on any
mosquitoes present. Wetlands are a critical element in a healthy
ecosystem that benefits people, water quality and wildlife. Wetlands
clean and slowly release rainwater and provide flood protection and
wildlife habitat. Many wetlands recharge groundwater and prevent streams
from drying up during the summer. We will not eliminate mosquitoes by
draining wetlands. We could actually increase the mosquito population if
their natural predators are destroyed by draining a wetland. Many
mosquito species need only a small puddle or depression in which to
breed.
Rivers and Streams
Under normal circumstances, mosquitoes cannot breed successfully in
flowing water, and therefore streams and rivers can only produce
mosquitoes when they dry up and leave shallow, stagnant puddles in the
stream bed or in backwater areas. Streams and rivers provide good
habitat for predators that feed on mosquitoes and mosquito larvae.
I live near a stormwater pond or a wetland and worry
about my family's safety.
We will never be able to eliminate all habitats for mosquitoes and not
all mosquitoes are carriers of the virus. Stormwater facilities,
greenways, and wetlands provide numerous health and quality of life
benefits. They clean pollution from air and water and reduce flooding
and erosion. Local and federal health experts recommend the best
personal protection is to reduce mosquito habitat, prepare your home and
take personal protection measures.
Reducing Mosquito Habitat
Mosquitoes lay their eggs in standing water. The eggs only need a few
ounces of water to grow into adults. Take these steps to reduce mosquito
habitat around your home.
- Eliminate places where water can stagnate in containers such as
buckets, flowerpots and tires.
- Change water at least once a week in birdbaths and wading pools.
- Clean clogged rain gutters, and put mosquito screens on rain
barrels.
-
Dispose of old tires or cover them so they don't collect water.
Prepare Your Home
- Put tight-fitting window screens on all your windows, and repair
rips or tears in existing screens.
- Consider adding a screen door to outside doors that are often left
open.
Personal Protection
We will never be able to eliminate all mosquitoes. Personal
protection is a way to avoid getting bitten. These particular mosquitoes
bite from dusk to dawn.
- Wear long sleeves and long pants.
- Consider wearing insect repellent that contains DEET. Read
repellent instructions carefully. Repellent should not be applied to
children under the age of two.
What is Redmond doing about West Nile Virus and
Mosquitoes?
Please refer to our
West Nile Virus Page
for
information.
If you have any further questions, please feel free to contact the
Natural Resources Division at 425-556-2825.
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