Environmental Engineering Reference
In-Depth Information
Figure 2.2. Schematic representation of
a grass filter strip along a road.
3.2.2
Catch basins
A catch basin is a runoff inlet chamber, which receives the storm water from the street
and conveys it into the drainage system. In contrast to ordinary inlet chambers, catch
basins are equipped with a sump at their base, which allows for the partial sedimentation
and retention of the heavy sand particles and debris, thus preventing the down stream
transport system from clogging and eliminating part of the pollution carried by the runoff.
The application of catch basins requires regular cleaning (desludging) of the sumps and
removal of retained material.
3.2.3
Grassed waterways and channel stabilization
The drainage system (separated sewer system), which conveys the runoff, usually
consists of open channels parallel to the roads/streets, which collect and transport the
runoff. In its downstream ends, or in specific topographic locations, underground pipes
might replace open channels. The design of the system requires the choice of an
appropriate size and type of channel and channel lining, based on the hydraulic and
hydrological data available, in order to transport the expected runoff quantity without
flooding and to prevent channel erosion. The most economic solution is to apply grassed
channels, where the grass provides for the necessary soil resistance to erosion. It should
be noted, that grassed channels provide not only the protection of the channel cross-
section, but also, as emphasized before, allows for partial infiltration and pollution
retention and assimilation. However, the grass should be cut regularly to avoid clogging
and the considerable reduction in the channel cross section. It is advisable to design the
grass channels with triangular and trapezoidal cross-sections and low slide slopes in order
to allow for mechanical grass removal, but this would increase the area requirements.
Measures to stabilize channels and to prevent erosion are necessary in specific
locations as sharp bends, channel drops and flow energy dissipators at discharge points.
