Attachment 1 - Op Works Negotiated Decision Notice · OPW11/0335

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OPW 11/0335

 

that erosion by all forms other than splash (raindrop impact) erosion and sheet
erosion does not occur; and

c) In areas of exposed soil where it is not feasible to either effectively stabilise the
surface or implement appropriate erosion and sediment controls, for example in the
areas being actively worked and where the implementation of some erosion and
sediment controls would impede construction activities, ensure contingency
measures are available on site and are implemented, prior to rain, to maximise
sediment capture and to minimise erosion such that erosion by all forms other than
splash (raindrop impact) erosion and sheet erosion does not occur

d) Effectively stabilise all stockpiles, batters and embankments without delay. Where
it is not feasible to effectively stabilise a stockpile, batter or embankment, such as
areas being actively worked, ensure that sediment controls are installed and
surface stormwater flows are managed such that erosion of stockpiles, batters or
embankments is not caused by concentrated stormwater flows.

e) For all works or other disturbances undertaken within waterways (including riparian
areas) ensure:

|. prior written approval from the relevant consent authority exists;

Il. Work within waterways must only be: undertaken during dry weather; be
promptly rehabilitated conforming to the natural channel form, substrates
and riparian vegetation as far as possible; and be undertaken in
accordance with Best Practice Erosion and Sediment Control, Appendix |
— Instream works, Sections 14 and 16, International Erosion Control
Association (2008); and

lll. Temporary vehicular crossings of waterways must be designed and
constructed to convey flows for the 1 in 2 year average recurrence
interval event (ARI) of critical duration and remain stable for all rainfall
events up to the 1 in 10-year ARI event of critical duration.

f) Ensure clean stormwater is diverted or managed around or through the site without
increasing the concentration of total suspended solids or other contaminants in the
flow and without causing erosion (on site or off site). If it is not feasible to divert all
areas discharging clean stormwater around or through the site, manage the clean
stormwater runoff in the same manner as contaminated stormwater runoff, and
ensure that sediment basins are sized to accommodate the additional volume of
runoff (See E&SC Advice Note 3).

g) Ensure sheet flows of stormwater are managed such that sheet and rill erosion is
prevented or minimised.

h) Ensure that all concentrated stormwater flows including drainage lines, diversion
drains, channels and batter chutes are managed onto, through, and at release
points from the site in all rain events up to and including the average recurrence
interval (ARI) event of 1 in 2 year ARI without causing water contamination, sheet,
rill or gully erosion, sedimentation, or damage to structures or property

i) Ensure measures have been implemented such that the runoff from all disturbed
areas flows to a sediment basin or basins. Where it is not feasible to divert runoff
from disturbed areas of the site to a sediment basin, implement compensatory
erosion and drainage controls prior to rainfall to ensure that erosion of those areas
does not occur, including erosion caused by either splash (raindrop impact), sheet,
rill or gully erosion processes (See E&SC Advice Note 4).

j) Ensure each sediment basin has the capacity to treat flows to current best practice
standards (see E&SC Advice Note 5) and as a minimum to contain all the
stormwater runoff from the 80th percentile 5 day rainfall depth and store 2 months
sediment from the receiving catchment, as determined using the Revised Universal
Soil Loss Equation.

k) Ensure sediment basins are maintained with sufficient storage capacity to capture
and treat the runoff for the design rainfall depth or event. Where sediment basins
are proposed to be oversized for storage of captured water for re-use, install

FM1509s/2-13/04/2011 Page 8 of 24