Reference Documents - MCU24 0141 & OPW24 0184 [As Published]

              4.3. Bioretention Basin Maintenance
              The proposed bioretention basin 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.


                        4.3.1. ‘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.


                        4.3.2. ‘Maintenance Period' Maintenance

              The bioretention basins will be temporarily turfed during the maintenance period. Once construction of the
              industrial units is complete, the turf will be removed and the basins will be vegetated appropriately.

              5. 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 has decreased slightly therefore no retention is
              required to manage stormwater runoff. The actual runoff to the council stormwater network will be reduced
              further due to the installation of the bioretention basin on the site.
              The subject site has an existing stormwater manhole which is identified to be the lawful point of discharge.
              The existing underground stormwater network is currently connected to this pit. The stormwater manhole is
              located in Acton Street which discharges to an existing 1650mm RCP stormwater main. The existing
              stormwater network ultimately discharges to Eenie Creek located approximately 600m to the south.
              A stormwater drainage system is proposed for the development which incorporates one bioretention basin
              and an underground drainage network to connect to the existing drainage. The northern portion of the site
              will discharge stormwater to the west by connecting to the existing stormwater gully pit on the site’s Leo Alley
              Road frontage. In the event that the stormwater pit over tops stormwater will discharge as overland flow to
              the grassed area through the site, located to the south as it does in the existing case.
              The southern portion of the site will discharge to the existing stormwater manhole located in Action Street to
              the east. In the event that the proposed network overtops stormwater will discharge as overland flow to the
              Acton Street roadway and enter the existing stormwater network via the existing gully pits located
              downstream on Acton Street as it does in the existing case.
              A majority of stormwater discharging from the site in the developed case will discharge to a bioretention basin
              which has an extended detention depth of 300mm. This equates to approximately 8.4 kL of total stormwater
              detention storage for the site. The stormwater detention volume will further reduce peak discharge.




240127 – Stormwater Management Plan             9 of 10