Stormwater Management on Site
Rainwater harvesting
Auckland’s rainfall is 1100 mm per
annum, with the average rainfall event contributing about 25mm. With
our rainwater harvesting system,
we expect to collect about 33 m3 during an average rainstorm.
The syphonic drainage system channels the roof water into a 25,000 litre main storage tank with two additional 25,000 litre tanks providing further detention capability. A small wind turbine provides sufficient energy to pump water back up to the header tank above the ethanol room.
The harvested rainwater is used for flushing ground floor toilets, urinals and for irrigating the glasshouses and gardens. (A mains backup is available for prolonged dry spells and for fire hydrants).
Stormwater detention
During prolonged wet spells, any overflow from the
detention tanks will flow into the raingarden area (still to be developed).
The
mix of soils
and organic matter acts as a giant sponge absorbing considerable
volumes of water preventing it from entering the municipl stormwater
system.
The car park has a pervious surface allowing the rainwater
to penetrate on the spot. Water in excess of what the soil can hold
will flow
through a treatment wall (to adsorb contaminants) then down
to the raingarden.
Water in excess of what the raingarden and the 10 litres /sec
soak pit can handle, will end up in the stormwater system but
this is
not expected
to happen very often.