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

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[OCR of page images]
OPW 11/0335

 

b. Best Practice Erosion and Sediment Control, International Erosion Control
Association (2008)

In this document, an effectively stabilised surface is defined as one that does not
- have visible evidence of soil loss caused by sheet, rill or gully erosion or
- lead to sedimentation, or
- lead to water contamination
Diverting clean stormwater runoff into a sediment basin is an inferior option to diverting
clean stormwater around or through the site because it will cause an increase in the
volume and frequency of contaminated releases from the sediment basin. For this
reason, diverting clean stormwater into a sediment basin is not acceptable unless the
nominated Proponent demonstrates that diverting clean stormwater around or through
the site is not feasible.

Compensatory controls are erosion controls, flow controls and sediment controls which
compensate for the lack of sediment basin and must be focussed on controlling
turbidity and not just coarse sediment. The controls are applied such that the type,
timing, placement and management of controls minimise the potential for water
contamination and environmental harm. This is primarily achieved by reducing the risk
of erosion and subsequent sediment release, for example by turfing or mulching and
managing concentrated flows in the area.

Research has shown that sediment basins designed on a “batch” or total storm
capture approach are only capable of treating a small percentage of the annual runoff
volume without basin size becoming excessive. Innovation in sediment basin design to
incorporate continuous flow treatment is likely to occur in the future. As this technology
gains recognition and support in best practice guidelines, Council will require that this
technology be adopted where it is likely that use of such technology will result in a
better water quality outcome. In the interim the minimum basin storage capacity is as
specified in the condition.

As a general rule, a site is determined to have achieved effective short-term
stabilisation if at the time of the plan sealing inspection:
Methods of stabilisation are:
e appropriate for slopes and slope lengths; and
e are consistent with best practice environmental management practices such
as in the Manual for Erosion and Sediment Control or the IECA Manual;
and
Stormwater runoff from the site is not currently, and is not likely to result in visible
evidence of sedimentation or erosion, or lead to water contamination.

If at the time of request for plan sealing, the method of short-term stabilisation has not
achieved a level of stability that Council's Officers believe will have a high probability of
achieving long term stability (i.e. until house construction has occurred on all lots),
Council Officers may take the following matters into consideration in determining
whether the site is capable of achieving medium to long-term stability:

Evidence that the site has been effectively stabilised in the short term;

Evidence that soil has been adequately ameliorated;

Evidence that seed of annual and perennial grass species has been applied at an

adequate rate; and

That grass seed has germinated at a density that is likely to achieve an effective

grass cover.
For example, while hydromulch can provide an immediate and effective stabilising
cover to soils, the protective cover can be relatively short-lived if vegetation fails to
establish before the thin layer of mulch decomposes. So if hydromulch is selected as
the method of temporary short term stabilisation, Council Officers will seek to confirm
that perennial as well as annual grasses are well established at the time of plan
sealing to reduce the risk of instability of the site in the medium to long term. As a
general rule, hydromulch will only be accepted as a “patch” fix and should comprise no

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