Detailed Stormwater Management Practice Design - Tauranga City ...

SMG-9 Figure 14c Raingarden at Mount Club Bowling Greens Car Park
SMG-9.4.4.1 Basic Design Parameters
The main components of a Rain Garden include:
a) Grass filter strip for minor pre-treatment (where space is available).
b) Ponding area in the extended detention zone.
c) Planting soils.
d) Ground cover or mulch layer.
e) Plant material.
f) Underdrain system.
Depending on the natural soils in the area that the Rain Garden has been placed,
final discharge of stormwater can be to ground or through a drainage system to
surface waters. This will depend on the permeability rates of the underlying soil,
depth to groundwater or bedrock and the stability of any slopes that the additional
water may be discharged within. In the situation where the eventual disposal of
stormwater is to ground, testing of infiltration rates needs to be done consistent with
infiltration practices shown in the next section.
It is not recommended that geotextile filter cloth be used between the different media
layers in the rain garden, as that will become a point of clogging in the filter. Proper
installation of the various layers of media (including the drainage layer) will reduce
potential migration of contaminants to the drainage system.
Rain Gardens are designed as water quality practices and will generally not be used
for water quantity control. If peak control is required and cannot otherwise be
provided then consideration should be given to a constructed wetland that also
provides peak control.
Page 29 Updated 01/11/2012