Attachment 7 - Stormwater Management Plan

                                 STORMWATER MANAGEMENT PLAN
Client: Devcon Capital 9                                               Location: 11 Leo Alley Road, Noosaville


3.3 Bioretention Basin Maintenance

The proposed bioretention basins will require consideration and management during both the
construction period and maintenance period of the development. In order to establish vegetation and
treatment functions in the bioretention systems, the filter media will require protection from the
common pollutants generated in the construction phases of the development. During the operational
phase, regular maintenance is required to ensure a comprehensive vegetation establishment, a
critical component in stormwater pollutant uptake. Below are details on the general maintenance
periods and the requirements for the construction and maintenance periods.

3.3.1 ‘Construction Period’ Maintenance

Erosion and sediment control devices will be installed at the commencement of the works to capture
and treat runoff during construction works. The sediment control devices should be cleaned out as
required and at the end of the works. During the construction stage, all sediment control devices are
to be inspected weekly, after runoff generating rain events and prior and after prolonged site shut
downs (e.g. holiday periods). Proposed bioretention basins may be excavated and used as a
sediment basin.

Any sediment basin will require regular, weekly inspection to prevent scour and sediment build up.
Basins should be inspected regularly and cleaned out when 1/3rd full. At the completion of
construction, the sediment basins will be removed. The bioretention basin will be installed at the end
of the building construction phase when the site is stabilised.

3.3.2 ‘Maintenance Period’ Maintenance

The bioretention basins will be temporarily turfed during the maintenance period. Once construction
of 80% of the site in each catchment of the development is complete, the turf will be removed and
the basins will be vegetated appropriately.

4.0 STORMWATER QUANTITY MANAGEMENT
The majority of the existing site is considered to be hardstand as the current use of the site is for
storing landscape supplies which are normally delivered and taken away from the site using heavy
vehicles. Due to the proposed development the fraction impervious of the site increases slightly from
80% in the existing case to 83% in the developed case. The time of concentration in both cases is
effectively the same as both sites have a similar fraction impervious.

The subject site has an existing stormwater pit which is identified to be a lawful point of discharge.
The existing underground stormwater network is currently connected to this pit. The stormwater pit
is located in an easement which discharges to an existing 300mm RCP stormwater main. The
existing stormwater network ultimately discharges to Eenie Creek located approximately 500m to
the south.

A stormwater drainage system is proposed for the development which incorporates a bioretention
basin and an underground drainage network. The northern portion of the site will discharge
stormwater to the east by connecting to the existing stormwater network within the easement. In the
event that the stormwater pit over tops stormwater will discharge as overland flow to the grassed
area located to the east as it does in the existing case.

The southern portion of the site will discharge to the existing stormwater manhole located in Leo
Alley Road to the south. In the event that the proposed network overtops stormwater will discharge
as overland flow to the Leo Alley Road roadway and enter the existing stormwater network via the
existing gully pits located downstream on Production Street as it does in the existing case.


Covey Associates Pty Ltd                            5                                   Project No: 192297
Consulting Engineers                                                                      26719Rpt, Issue D