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

7 Protect critical areas.
8 Inspect and maintain control measures.
4.2 Erosion and Sediment Control Measures
To mitigate the effects of earthworks on the receiving environment (SES13) works shall be timed to
coincide with periods of low flow and completed as quickly as practicable. If conditions are not
suitable, such as periods of heavy rain, works shall be stopped. Further to this the programmed
time of works shall avoid fish spawning seasons, especially in regard to sensitive species such as
whitebait, as detailed by the Operative Regional Water and Land Plan.
As water from the site discharges to a sensitive receiving environment, sediment control is of high
importance and therefore works will be undertaken in line with best practice methods. The following
plans, and subsequent Contractor’s plans, will be prepared in accordance with EBOP guidelines
2001/03.
This section gives a description of possible erosion and sediment controls that may be implemented
by the earthworks Contractor on site. Due to the complexity of construction and the options
available it is expected that the below methods will be superseded by a detailed ESCP prepared by
the Contractor, and will be updated continuously as works on site progress. Any changes in plans
will be reviewed and approved by Environment Bay of Plenty before works begin in the area
covered by the plan.
4.2.1 Mangatawa Drain
Plan 3932036-C142
While the volume of earthworks excavation associated with the Mangatawa Drain maintenance is
only 200m 3 at most, the volume associated with the Kairua Road storage area within the
Mangatawa Drain is approximately 28,000m 3 . Further to this there is approximately 4,000m 3 of fill
works associated with the top spill bund alongside the drain.
Clean water diversions will be placed along the northern boundary to divert clean flows from the
working footprint and reduce the catchment requiring treatment. Due to the level of earthworks and
the required work within the drain a decanting earth bund will be installed across the drain upstream
of the Rail Bridge Embankment Stability works. Sediment laden flows from the upstream works will
be treated by the decanting earth bund prior to discharging to the drain just upstream of the rail
bridge. Ideally woks will be undertaken during periods of low flow so as to avoid the potential for
effects on the downstream environment.
During works in this area careful consideration will be given to the weather forecast and works will
only commence if the following 24hour period indicates no significant rainfall. www.metvuw.co.nz
will be utilised for this purpose.
Further to this, works associated with the increased drain storage area east of Kairua Road will be
segregated from the drain to reduce the potential for sediment to enter the waterway. This shall be
through the use of either silt fence or sand bags depending on the level of flow within the drain.
4.2.2 Rail Bridge Embankment Stability
Plan 3932036-CK473
To stabilise the drain embankment beneath the rail bridge a rock anchored concrete retaining wall
shall be constructed. The space for construction beneath the bridge is limited and as such only
small equipment and machinery will be used. Due to the nature of the works and the potential for
Beca // 1 April 2009 // Page 6
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