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

NZ Transport Agency and Tauranga City Council
Mangatawa Drain Flood Bypass and TEM Stormwater AEE
In addition, the mitigation proposed to control the temporary effects of the earthworks on the environment, as
well as the attenuation and treatment proposed to manage the effect of the stormwater, will be consistent with
Objectives 10, 17 and 19. The Project will also provide for the beneficial effects of providing a key
transportation corridor.
Chapter 4.0 – Discharges to Water and Land
Discharges of Contaminants or Water to Water, and Discharges of Contaminants to Land and 4.2 Discharge of
Stormwater.
Provisions relating to discharges to land and water are contained in the RWLP in Objectives 23, 26, 31, 32, 34
and Policies 38, 39, 42, 50, 51, 54, 56 and 57.
The proposed stormwater management philosophy for the TEM is to maintain or enhance the quality of
stormwater prior to its discharge to the local streams and rivers. Management of stormwater related to
flooding and treatment were major concerns of surrounding landowners, hapu and most of the stakeholders
during the consultation process. NZTA has undertaken to meet the ARC TP10 level of treatment for road way
derived stormwater while mitigating the risk of flooding through attenuation of the stormwater created by the
motorway. In this way, the Project addresses the concerns of the submitters and affected parties in the
Project.
The Mangatawa catchment is predominantly rural and the runoff from this land is likely to contain typical rural
nutrients and contaminants. Treatment of this runoff is not part of this project and will continue as it does
currently as the land management practices of this catchment are beyond this projects ability to practically
control.
With regard to the accidental spillage of hazardous substances during TEM construction, this will be managed
through the Environmental Safety Plan which will show what measures will be taken to protect the environment
from accidental spills. It is intended that these measures will be in place before construction located
appropriately.
Chapter 6.0 - Beds of Rivers, Streams, Lakes and Wetlands
Activities in the Beds of Rivers, Lakes and Streams
Objectives 55, 57, 58, 59, 73, 74 and Policies 98 to 102, 133, 134 of the RWLP relate to the beds of rivers,
streams, lakes and wetlands.
The construction works required in the Upper Mangatawa Drain will have a temporary effect on the ecological
value of the drain. These works require the drain bed to be lowered through excavation; coffer dams to protect
the placement of gabion baskets and reno mattresses; and protection of the flow path from the construction of
the strengthening embankment at the rail bridge. The works will only affect the ecological value of the stream
for short periods if managed appropriately.
The principals of the philosophy to mitigate these effects are laid down in the example Erosion and Sediment
Control Plan in Appendix 13. The drain itself is a highly mobile environment with a sandy bottom and the flora
and fauna found in this drain will be well used to high levels of sediments from high rain fall events.
Status: Final Page 101 April 2009
Project Number: 3932036
NZ1-1552092-Mangatawa Drain Flood Bypass and TEM Stormwater AEE