2. Mangatawa catchment consents for earthworks, storm water ...

NZ Transport Agency and Tauranga City Council
Mangatawa Drain Flood Bypass and TEM Stormwater AEE
• Species of vegetation used in swales
• Source of the fill for earth works
• Volume of water in the Mangatawa Drain
Mitigation measures addressing these issues are as follows:
i. Planting strategies for the TEM swales will include wetland vegetation appropriate for the swale
environments which will assist in the treatment of the stormwater prior to discharge to the receiving
watercourses.
ii.
Planting within the riparian margins of the Mangatawa Drain will aim to enhance the habitats where
practicable through native, non-invasive species.
iii.
TEM TWAG has prepared a detailed earthworks protocol which will apply to this area as well as the
remainder of the project site.
iv.
Modelling undertaken in the development of the stormwater management system design has
incorporated flood levels adjusted for climate change to ensure appropriate treatment and controlled
discharge rates to the harbour.
v. Maintenance of the TEM swales will not utilise sprays and vegetation will be replaced as required (likely
to be approximately every 20 years). An asset management plan will be maintained by NZTA for the
ongoing maintenance of the system.
vi.
Appropriate measures will be taken to ensure that the TEM and TCC culverts are designed to ensure that
passage for fish throughout the existing watercourses is maintained and works in the Mangatawa Drain
will be undertaken outside of the spawning periods as defined the by the RWLP. It is not proposed that
fish passage be provided from the storm water treatment wetland or the Mangatawa drain up into the
Maranui Swale as these areas are not ecologically significant.
vii. The treatment provided by roadside swales and the enlarged TCC treatment pond will reduce the
contaminants entering the Mangatawa Drain and Rangataua Bay from existing developments and the
TEM developments.
The potential of the Mangatawa drain for food gathering purposes was raised during the consultation as
important to Nga Potiki and other users of the drain. Preventing the stormwater from the TEM alignment from
entering the upper and lower Mangatawa Drain, and the proposed recreation and access improvements on the
Lower Mangatawa Drain will provide positive benefits to the users of the lower waterway in these aspects.
NZTA is continuing dialogue with Nga Potiki and all other Tangata Whenua groups through the TEM TWAG as
the project proceeds into final contract design and construction.
These actions reduce the effects of the proposal to a no more than minor level.
Status: Final Page 94 April 2009
Project Number: 3932036
NZ1-1552092-Mangatawa Drain Flood Bypass and TEM Stormwater AEE