In May 2005, floods affected the northern region of Tauranga
city resulting in the inundation of many properties. In
response to the flooding, Tauranga City Council implemented a
city-wide Storm Recovery Programme. A major component of the Storm
Recovery Programme was the Aerodrome Road Stormwater Catchment
Upgrade, which began in September 2006 with capital works forecast
at $5.6 million.
The Aerodrome Road stormwater catchment is
widespread, covering 26 hectares in Mount Maunganui. The
environment is particularly complex as the catchment’s drainage
flowed west via open drains and pipelines between buildings on
private property to the harbour at the Port of Tauranga. As
this drainage was in a developed area, the upgrade could not be
realistically undertaken without disruption to existing property
owners and occupiers, and at a considerable cost to ratepayers.
The planning for the project started in
September 2006. Working together GHD and Tauranga City
Council facilitated a feasibility study and options assessment
encompassing risk evaluation, hydraulic modelling and upgrade
alternatives. GHD was then commissioned to provide the
council with design options. Contract administration services
for the physical construction works of the project were also
provided by GHD.
Consents were obtained from Environment Bay of
Plenty, Transit New Zealand and Tauranga Airport. Consent was also
required from ONTRACK (part of KiwiRail Group - New Zealand
Railways Corporation) as the pipeline crossed a railway designation
in upper Aerodrome Road and required design alterations to
facilitate future railway crossing and pipeline
The scope of the project involved the
redirection of stormwater southwest from the Aerodrome Road
catchment via a pipeline running from Newton St, along Aerodrome
Rd, across Hewletts Road and passing through four industrial
properties, Harvard Way, crossing under Jean Batten Drive and
through Tauranga Airport. This involved a number of design
and construction challenges, in particular, the flat topography of
the catchment which imposed gradient limitations on the pipeline
and open drain.
GHD addressed client concerns via
comprehensive risk analysis and the expected cost of professional
Stormwater modelling utilised Tauranga City
Council’s MOUSE hydraulic model which was updated with sub
catchment boundaries based on Tauranga City Council GIS data and
maximum probable development information. The hydraulic model
was then updated with Tauranga City Council’s ‘high intensity
rainfall’ information and ‘tidal boundary conditions’ relating to
the proposed outlet in Waipu Bay. The ‘Brownfield Philosophy’
was also implemented to utilise the existing stormwater system.
The crossing under Hewletts Road (SH2)
presented challenges in relation to the structural integrity of the
box culvert, pavement and the management of existing services. It
was also paramount that two-way traffic was maintained at all
times. Initially, the plan was to tunnel under the road however
this plan was abandoned due to hydraulic flow restrictions and the
location of strategic services under the road.
In consultation with Transit New Zealand, a
decision to adopt an open cut methodology, by working 24/7 was the
best option. The crossing at Hewletts Road consists of 41
metres of 3.5m wide by 1.7m high box culverts and provides for
maximum stormwater flows and sufficient clearance under critical
Connell Contractors Limited carried out
construction work for the Stormwater Catchment Upgrade and Stage
One was successfully completed in February 2008. Connell
widened and installed erosion protection in the existing 800 metre
long open drain and upgraded both the structure at the harbour
outlet and existing stormwater outlets into the drain.
In March 2008 Connell began constructing the
new pipeline from the upgraded open drain to Newton St.
Construction was completed in June 2009 of the pipeline across Jean
Batten Drive, along Harvard Way and the pipeline that runs through
private industrial properties in and across Hewletts and Aerodrome
Roads and Newton St.
One of the council’s key objectives was to
minimise disruption to the general public in Hewletts Road as it is
the main arterial route that connects Tauranga central business
district with Mount Maunganui. Potential safety issues and
disruption at Tauranga Airport were managed in close co-operation
with the Airport and Civil Aviation authorities. The seasonal
nature of businesses was also a factor and pipeline installations
were scheduled accordingly.