RFI - Attachment 3 - Stormwater Management Plan

Internal Catchment Areas for DRAINS Modelling
Project number:    21020                                                Calculations:                         B. Parry
Street Address:    55 Carpenters Road
Locality:          Cooroy, Noosa Council                                Date:                                 27/07/2022


Existing Site
                                             Existing Site              Directly connected (m²)               Indirectly connected (m²)
Lot 2 RP 200519       Roof                                      474.1                                  -                                     678.6
                      Impervious Ground                         359.7                                  -                                   1,181.5
                      Road                                        -                                    -                                     750.3
                      Total Imp                                 833.8
                      Total Per                              23,476.6
                      Site Area                              24,310.4                                  -                                   2,610.4

% impervious                                                            Effective DCIA = 75% DCIA             ICIA +25% ineffective DCIA
                                                                                                          0                                 2610.4
                      Impervious                                 3.4%                                  0.0%                                  10.7%
                      Pervious                                  96.6%

Time of Concentration

Roof Drainage
     Older dwelling                       2.0 mins                      (per DRAINS recommendations)

Sheet flow (Friends Eqn.)
             Length                    188 m
         Horton's n                  0.045 Average grassed
  Fall over distance                    9.5 m
               Slope                    5.1 %
                Time                  20.0 mins


         Total Time                   22.0 mins

Proposed Site
                                             Proposed                   Directly connected (m²)               Indirectly connected (m²)
Lot 2 RP 200519      Roof                                     3,135.4                               3,135.4                                    -
                     Impervious Ground                        2,029.5                                   -                                  2,029.5
                8878 Road                                     4,831.0                               4,831.0                                    -
                     Total Imp                                9,995.9
                     Total Per                               14,314.5
                     Site Area                               24,310.4                               7,966.4                                2,029.5

% impervious                                                            Effective DCIA = 75% DCIA             ICIA +25% ineffective DCIA
                                                                                                    5,974.8                                4,021.1
                                                                41.1%                                 24.6%                                  16.5%
                                                                58.9%

Standard Inlet Time (QUDM Table 4.6.2)
               Time                  13.0 mins

Pipe Flow (Mannings Eqn)
             Length                    335 m
    R (375 dia pipe)                0.1875 m
              Slope                  0.031 m/m
      n (Manning's)
         Table 9.3.4                 0.013
               Time                     1.3 mins

         Total Time                   15.0 mins