Managing stormwater is one of Auckland City's many activities.
Auckland City aims to protect Auckland's unique and valued
environment and allow for future urban growth. It is Auckland
City's job to assist Auckland's residents to make sure stormwater
is managed properly on their land, and to safely remove stormwater
across the city.
Auckland Transport’s drainage assets consist
of approximately 27,500 catchpits, 2,300 soakholes and 550 manholes
within Auckland’s central city and the Hauraki Gulf islands.
The condition and performance of these structures is critical not
only to the city’s wider drainage and reticulation system, but also
to the efficiency, safety and reliability of the transportation
Auckland Transport has undertaken an
extensive drainage renewal programme. In 2008, GHD won a three year
asset management contract to assist Auckland Transport in
delivering its stormwater strategy through a road contaminant
The programme aim was to prevent the entry
of road pollutants to Auckland’s waterways and harbour via the
stormwater system and, in so doing, help Auckland Transport meet
its strategic goals for environmental protection.
Senior Water Engineer and Principal Asset
Manager, John Tetteroo explains what concerns him when the water
hits the road.
“Maintenance of these assets is
becoming increasingly complex as urbanisation intensifies.
Complicating factors include greater stormwater loading on the road
drainage network, large numbers of trees, utility services that
restrict installation of new drainage, and increased on-street
parking making it difficult to access structures.
From a broader environmental perspective,
stormwater run-off from new and infill housing developments is
affecting stormwater quality. With climate change predicted to
increase occurrences and intensity of rainfall events, there is the
potential for increased private property and carriageway
In recent years, councils have explored a
number of options for treating stormwater discharge from
carriageways. These include expensive end-of-line treatment
solutions, such as stormwater ponds and wetlands, and at-source
treatment devices such as sand filters, rain gardens, swales and
catchpit filter bags.
However in the urban context, these
solutions are not often practical due to space limitations,
retrofitting requirements and maintenance issues.
Historically, little development had occurred around the
performance of existing catchpits as the first point of opportunity
for stormwater treatment.
GHD has created innovative and sustainable
solutions to overcome stormwater issues within the road reserve,
implemented best practice asset management techniques, and develop
actions that are linked to strategies.
Best practise operational procedures such as
GIS spatial analysis have been applied to manage a range of
stormwater data. GHD is also working with Auckland Transport on
reducing pollutants discharging to the receiving waters of the
harbour, including specially designed soakhole filters and catchpit
pollutant trap devices.
GHD have developed, trialled and tested the
low maintenance “TetraTrap” catchpit pollutant trap. When
inserted in catchpits, increased sediment capture (75-175%)
together with an optimised road sweeping and catchpit cleaning
programme significantly improves the quality of stormwater
discharge into the receiving environment.
Working closely with Auckland Transport, GHD
has instigated an innovative and environmentally sustainable
initiative to help manage road stormwater contaminants within
The application of these new innovations
throughout the city will enhance the city’s stormwater assets,
reduce stormwater pollution and nurture a healthy
The significant achievements of the
programme were recognised by the industry when GHD received the
prestigious Institute of Professional Engineers New Zealand Arthur
Mead Award for Environment and Sustainability 2011.