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

NZ Transport Agency and Tauranga City Council
Mangatawa Drain Flood Bypass and TEM Stormwater AEE
9.2 Earthworks
The Earthworks for the construction of the TEM embankment and associated swales has been assessed and
considered at a hearing finishing on December 18th 2008. This application will address the earthwork effects
related to the construction of the Mangatawa Catchment Stormwater management.
The total volume of earthworks required to be undertaken is approximately between 45,000m³ - 60,000m³.
NOTE: This excludes the works which will be subject to a separate resource consent application.
The effects of earthworks and construction can result in increased, erosion, sedimentation, nutrient levels in
riparian margins and waterways as well as more human effects such as increased noise, dust and vibration.
This can have an adverse have an adverse effect on ecological values, cultural values, natural character and
landscapes.
9.2.1 Ecological Effects from Construction
For this proposal there is a potential temporary adverse effect on the ecology of the freshwater habitats in the
downstream receiving environments, through sediment inputs from construction and maintenance operations.
During construction the main activities with the potential to generate harmful ecological impacts are:
1. Works in the bed of the upper Mangatawa Drain
2. Construction of the stormwater treatment wetland
3. Construction of the earth stopbank on the Lower Mangatawa Drain
NZTA and TCC will seek to manage and mitigate these effects through establishing environmental bottom lines
in its contract documents with the contractor.
It is recognised that the upper and lower drain has significant importance to the local community. The use of
the drain to eel and catch white bait was raised during consultation and to support this activity works in the
bed of the stream will be undertaken outside fish spawning periods to lessen the impacts of this disturbance.
Works to improve and stabilise the drain alignment past the railway bridge, using gabion baskets and reno
mattresses, will be undertaken as quickly as possible to minimise disturbance. The banks of the drain will be
re-established and planted as soon as is practicable after the activity takes place and it is proposed that any
complaints and or issues that the community may have be dealt with quickly and directly with the contractor
through a complaints phone line set up for this project.
The result of these mitigation measures will mean that the effects of this activity will be no more than minor.
The construction of the stormwater treatment wetland will take place next to the SES as described in the
project description. Using a Construction Management Plan (CMP) as defined below will address many of the
issues related to earthworks for this and other earthworks activity.
Status: Final Page 89 April 2009
Project Number: 3932036
NZ1-1552092-Mangatawa Drain Flood Bypass and TEM Stormwater AEE