Stormwater Management Plan

                              STORMWATER MANAGEMENT PLAN
Client: Hass Holdings ATF The Quasar Trust                               Location: Taylor Court, Cooroy


5.0 MAINTENANCE PERIOD
5.1 Bioretention Basin

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

5.1.1 Maintenance During ‘Construction Phase’

Erosion and sediment control devices will be installed at the commencement of all the staged
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).

Following construction of the roadways and buildings on site the basin will be constructed to the
final design and filter media layers and plants will be installed. Leaving the completion of the
bioretention basin until after construction is completed will prevent any potential clogging of the
system during the construction period.

6.0 STORMWATER QUANTITY
The proposed stormwater quantity management for this site ensures non-worsening of flows as a
result of the proposed development. Development of the site will result in an increase in
impervious area and a corresponding increase in peak stormwater runoff rates which will be
mitigated through on-site detention. This section of the report encompasses the hydrological and
hydraulic analysis for the proposed development and identifies the stormwater detention measures
required to ensure non-worsening conditions.

6.1 Stormwater Quantity Management

An analysis of the stormwater (quantity) required for the site, involved the following processes:

      Determining the overall catchment areas contributing to flow from the proposed development
       site;
      Calculating the 1%, 10% and 39% Annual Exceedance Probability (AEP) peak discharges
       using XP-RAFTS for existing case;
      Rational method calculations for comparison and calibration of the XP-RAFTS runoff model
       to ensure the accuracy of results; and
      XP-RAFTS detention modelling for the 1%, 10% and 39% AEP design discharges to
       demonstrate that peak discharges are mitigated in the developed case and flows leaving the
       site are ‘non-worsening’.

6.2 Hydrology (XP-RAFTS)

XP-RAFTS was utilised to determine the peak stormwater discharges for the subject site for pre-
development and post-development scenarios.



Covey Associates Pty Ltd                     6                                       Project No: 161968
Consulting Engineers                                                                    100415 Rpt Iss A