Change application_280920 · MCU18/0120.01

             provide screening planting along the bioretention basin batter as a means to facilitating the
             finalisation of plan sealing.

As discussed on the phone, there are some positive outcomes from the as-built solution that we
strongly recommend are considered.

    •        The filter media surface area is greater than the approved design.
    •        The filter surface is located away from the large upper retaining wall that separates the
             bioretention basins and car park area. This maximises the batter distance between filter area
             and the ground supporting the retaining wall. The retaining wall is now much less likely to
             settle and exert pressure on the filter media thereby compacting it and reducing its hydraulic
             conductivity. There is also increased length of scour control to dissipate inlet water velocity
             before it reaches the filter media surface and causes possible scour.
    •        Hydraulic short circuiting is prevented with the geofabric liner wrapped up the block walls and
             around the overflow riser pits and back under the filter media layer
    •        Cane mulch and netting is provided across the filter surface to prevent weeds taking root
             during the establishment phase. Given how much Singapore Daisy is in the area, this is a good
             outcome.
    •        Any loading in of materials or replacement plants can use the wider batter area between filter
             media and car park retaining wall to place stock, tools and materials so the filter surface is not
             over compacted during maintenance.

It is acknowledged that retaining walls to the southern basin perimeter inhibit the ability to enter the
basin for maintenance. Access to the basins can either be from Bio Basin #1 which is closest to the
road and has the lowest height retaining wall around its perimeter or from the drainage reserve land
along the southern boundary to all three basins.

Given this system is a private Stormwater Quality Improvement Device to be managed via the CMS for
the overall development, maintenance contractors can attend site with the correct equipment (e.g.
short ladders) to maintain the basin areas. Whilst this is not ideal, the accessible perimeter on the
approved design was always via the adjacent drainage reserve land to the south. If contractors were
not allowed to access this land for maintenance reasons, the access outcome directly from the
development site is the same as on the stamped approved plans by HR Design.

We are of the opinion that the as-built bio retention basin treatment devices are constructed such that
they will fully perform their intended function to treat stormwater runoff from the subject site and
assist in maintaining the health of the downstream watercourse. The larger filter media area, surface
treatment to aid in macrophyte establishment, perimeter geofabric liner treatment to prevent water
short circuiting, and increased rock scour pad distance is of benefit to the establishment and longevity
of the device. Access for maintenance purposes can still be managed by a landscaping contractor with
the correct equipment.

MINOR CHANGE

Planning Act 2016 defines a minor change as:

A minor change, for a development approval, is a change to the approval that —

        i.       would not result in a substantially different development; and

             The DA Rules state:

             In determining whether the proposed change would result in substantially different
             development, the assessment manager or referral agency must consider the individual
             circumstances of the development, in the context of the change proposed.