B07056.W-01A Complete - Stormwater [As Published] · 132007.2398

Concept Stormwater Management Plan
RSL Care – Cooroy Retirement Village



7.0        WATER BALANCE MODELLING
Noosa Council’s Planning Scheme Policy requires the development to demonstrate no increase in average
annual runoff volumes from the site. In order to demonstrate this, a water balance simulation was undertaken for
the:
      •   Existing Scenario – the site in its predevelopment state;
      •   Developed Scenario – the site developed without the proposed management strategies; and
      •   Mitigated Scenario – the site developed with the proposed management strategies included.

The aim is to show that management strategies proposed will significantly reduce the increase in runoff volume
resulting from the development to existing or near existing volumes.

7.1                Proposed Measures
The following strategies will be employed to reduce potable water demand from the development:
      •   Efficient Water Use – to maintain a constant supply of water from a limited source, efficient water usage
          and design principles will be incorporated throughout the development. This will include at minimum
          AAA rated water saving devices (such as dual flush toilets, low-flow showers and faucets, front loading
          washing machines and efficient dishwashers) and pressure management. Landscaping incorporating
          water efficient vegetation will also be incorporated throughout the development.
      •   Rainwater Capture and Reuse – Four underground rainwater tanks with a total capacity of 700kL are
          proposed. Captured rainwater from the underground tanks will be used to supply water for toilets,
          laundry and external purposes for all ILU’s. The two Apartment buildings and the Residential Aged
          Care (RAC) building will reuse rainwater for toilets and laundry. Landscaping will also be irrigated by
          captured rainwater.

7.2                Water Balance Methodology
7.2.1              Rainfall Data

Daily rainfall data necessary to undertake the rainwater tank analysis was taken from the Rainman Professional
Edition Version 4.3, published by the QLD Government Department of Primary Industries (June 2003). Rainfall
data was analysed from the Cooroy Composite Station 1.5 km south of the site.

The relevant mean yearly rainfall for the 108 year period of available data for the Cooroy station was found to be
1602 mm. The yearly rainfall data was then analysed to determine which consecutive 30 year average was
closest to the average of the entire data set. This was determined to be from 1928 to 1957. Within this period,
10 and 90 percentile rainfall years occur as for the total 30 and 100 year periods.

Table 7.1 compares the 100 year period and the 30 year period relevant parameters.
                                    Table 7.1: Comparison of 100 & 30 Year Periods
                    Parameters Compared          100 year period (mm)         30 year period (mm)
                           Mean                          1602                         1576
                           10%ile               1184 (1187mm for 1940)       1247 (1254mm for 1951)
                           90%ile               2184 (2183mm for 1950)       2262 (2260mm for 1956)




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