Stormwater Management Plan

SC5551 - 28 Elkhorn Dr, Tewantin                                                                                 8




Under the proposed conditions, the site was ‘split’ into three land use catchment nodes; the roofed area,
driveways and ground level uses. The pollutant export parameters utilised were based on the Urban
Residential pollutant loads, refer Table 3.3 & 3.4.


                       Parameter                                                      Value
                Rainfall threshold (mm)                                                1
              Soil storage capacity (mm)                                              500
              Initial storage (% capacity)                                             10
                  Field capacity (mm)                                                 200
          Infiltration capacity coefficient (a)                                       211
           Infiltration capacity exponent (b)                                          5.0
                   Initial depth (mm)                                                  50
                Daily recharge rate (%)                                                28
                Daily baseflow rate (%)                                                27
             Daily deep seepage rate (%)                                               0
                        Table 3.3 – Rainfall-runoff Parameters Adopted (Urban Residential)



                                              TSS Log                 TP Log                         TN Log
 Flow Type       Surface Type
                                      Mean        Std Dev.    Mean        Std Dev.            Mean       Std Dev.
                      Roof              N/A         N/A        N/A             N/A            N/A             N/A
  Baseflow
                   Driveways            1.00        0.34      -0.97            0.31           0.20            0.20
Parameters
                 Ground Level           1.00        0.39      -0.97            0.31           0.20            0.20
                      Roof              1.30        0.39      -0.89            0.31           0.26            0.23
 Stormflow
                   Driveways            2.43        0.39      -0.30            0.31           0.26            0.23
Parameters
                 Ground Level           2.18        0.39      -0.47            0.31           0.26            0.23
                         Table 3.4 – Pollutant Export Values Adopted (Urban Residential)



3.3.2.1 Rainfall Data
Rainfall data for the site was chosen to give the best representation of actual conditions. A time period of
10 years between 1973 and 1983 was selected from the Cooroy Composite station, using a six minute time
step.