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Cold climate urban drainage issues

January 4, 2014

It all becomes MORE complex in cold weather months
than in the warm weather months of the year.

Snowfall and low temperatures cause problems
to the urban drainage systems around town.

Cold temperatures

Cold temperatures

Storm runoff is affected by:
a) frozen ground surfaces
b) frost penetration
c) snow on ground
d) rain-on-snow
e) snowdrift
f) Man-made snow redistribution
g) snow removal

Additional problems are caused by frost heaving,
freezing in pipes, ice on ground surfaces,
clogging of gutters and inlets,
icing in manholes and in storm sewers,
ice in open watercourses such as urban creeks.

There are also changes in the transport of
urban runoff and stormwater pollutants,
the operation of runoff control facilities
and sewage treatment plants.

Snow may be stored on the catchment and produce
runoff during warmer weather.
Frozen ground thaws slowly and high runoff rates
may occur when rain falls on frozen ground.

Other problems are due to flooding,
combined sewer overflows (CSO)
and overloading of wastewater treatment plants.
Pollutants may be accumulated in the snow in streets.
When the last 10–20 % most polluted part of
the accumulated snowmelts and enters the sewer system,
a shock load of pollutants may occur.
The sewer system is filled up from previous inflow and
a part of the concentrated pollutants may be discharged
in overflows to local recipients.

The wastewater conveyed to the treatment plants is ice cold,
due to high inflow/infiltration in rain-on-snow
and melting periods. Problems to the urban surface runoff
are caused by the snow redistribution on sidewalks etc
or temporary surface water storage because of clogged inlets.
In cold climate areas the planning and designing procedures
for urban drainage often do not consider the
presence of the snow and even not the operation
and maintenance procedures and guidelines.

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