FLOOD09481

• County: Statewide
• Community: State
• Stream Name: All
• Basin: Statewide
• Title: Practices in Detention of Urban Stormwater Runoff
• Date: 1/1/1974
• Prepared For: American Public Works Association
• Prepared By: American Public Works Association
• Floodplain - Doc Type: Educational/Technical/Reference Information

practical solution to problems of urban
stormwater runoff management.
Categories of Maintenance and
Operation: There are several categories into
which maintenance and operation of
storm water detention facilities can be
classified. These include:
1. algae and aquatic vegetation control,
2. mosquito control,
3. pollution problems,
4. debris removal
5. sediment removal,
6. safety features,
7; maintehance of hydraulic facilities and
equipment such as pipes, channels
control gates and pumps, and
8. general maintenance.
Algae and Aquatic Vegetation
Control: Problems of algae and other aquatic
vegetation can plague all types of detention
facilities, whether they be rooftops or
permanent wet ponds. If the detention
facility is designed to be dry during most of
the time, the best method of vegetative
control is to design the facility to dry out
quickly and completely. A small puddle
standing for weeks on a parking lot will allow
algae growth to become a problem and such
depressions should be regraded to eliminate
standing water. In a large pond with a grass
bottom, natural drainage might allow pockets
of water to remain for long periods of time,
and the use of drain tile can assist in drying
out the pond to prevent such problems.
In ponds which have a permanent body
of water, algae problems will be more difficult
to control. The stormwater may be rich in
nutrients, acting as fertilizer for the algae.
Minimizing the pollution content of the
runoff by controlling erosion and practicing
gnod street cleaning habits will reduce the
algae problem. Although there are chemicals
available to kill the algae, the subsequent
decay of the algae produces odors and returns
the nutrients to the water, providing fertilizer
for further algae growth. In continually wet
ponds there are also problems of cattails and
other vegetation growing in the pond. Water
depths exceeding four feet will effectively
prevent these growths.
The major purposes of preventing
growths of aquatic vegetation are for
aesthetics, to minimize organic decomposition

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of plant material, to facilitate recreation, and
to minimize clogging of the outlet drains.
Even with proper management of detention
ponds, there will be some aquatic plant
growth, but such growth can be minimized.
Mosquito Control: Control of mosquito
breeding is similar to the control of algae
growths. Dry storage facilities should be
managed to prevent any water from standing
for a long enough time, usually four days, to
allow mosquitoes to breed. In permanent
ponds of water, mosquito breeding problems
can be controlled by stocking fish which will
eat the larvae. Other methods include using
chemicals to kill the larvae and the
maintenance of sufficient water flow to avoid
the stagnant conditions that are necessary for
mosquito breeding. With the latter method, it
is particularly difficult to insure satisfactory
results, as the water near the shoreline will
provide a suitable area for breeding.
Pollution Problems: Pollution problems
of stormwater detention facilities will be
limite d to those ponds that contain a
permanent body of water. The pollution will
result from runoff which picks up street
debris, oils from automobiles, other street
contaminants, fertilizers and pesticides, and
wastes contributed by users of the ponds. A
large pond of about 20 acres might allow the
use of boats with motors. In this instance, oil
and gasoline will be found to pollute the
water. Because of the nature of the water
source, it cannot be expected that the water
in a detention pond will be of high quality;
but recognition of the sources and types of
pollution is important nonetheless. Detention
storage of runoff would be expected to have
favorable consequences for downstream water
quality because of dilution provided along
with some in-storage treatment by natural
processes.
Debris Removal: Debris removal is a
maintenance requirement for all types of
detention facilities to prevent blockage of the
drains. Litter, grass clippings, leaves, tree
branches, and miscellaneous debris can find
its way into any type of facility although
some facilities will be affected more than
others.
Surface drains in a parking lot detention
facility at a shopping center will be especially
susceptible to blockage by litter. Although

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