Response to Information Request 20220004 -Tunba Court

Rational Method Calculations
Project number:                                     20220004                                                                                                           Calculations:                                        B. Parry
Street Address:                                     36 Tunba Ct
Locality:                                           Cooroy Mountain, Noosa Shire Council                                                                               Date:                                                8/02/2022



                                                                                                                      Catchments Assessment for Spoon drain sizing

Upstream Catchment                                                                                                                                                     Earthworks area (assuming future development)
                                                                                   2                                                                                                                                                             2
Impervious surface                                                            0 m                                                                                      Impervious Surface (Rural - fi = 20%)                             320 m
                                                                                 2                                                                                                                                                            2
Permeable Area                                                             6500 m                                                                                      Permeable Area                                                   1280 m

Total Site Area:                                                           6500 m2                                                                                     Total Site Area:                                                 1600 m2


Time of Concentration                                                                                                                                                  Time of Concentration
Existing Site                                                                                                                                                          Existing Site
                         Standard Inlet time                                  0 mins                                                                                                                 Standard Inlet time                   5 mins

Sheet flow (Friends Eqn.)                                                                                                                                              Pipe Flow
                                        Length                              133 m                                                                                                                          Flow distance                66.00 m
                                   Horton's n                              0.06 Densely grassed                                                                                                                    Slope                    1 %
                            Fall over distance                               49 m                                                                                                                          Pipe Diameter                 0.45 m
                                         Slope                             36.8 %                                                                                                          Flow velocity (Mannings eqn.)                 1.79 m/s
                                          Time                             15.9 mins                                                                                                                                Time                 0.61 mins

                                               Tc                          16.0 mins                                                                                                                               Time                   6.0 mins


Rational Method - Peak Flow Calculation
Upstream Catchment                                                                                                                                                     Earthworks Pad (assuming future development)
                                Area (Ha.)                                0.650 Ha.                                                                                                                           Area (Ha.)                0.160 Ha.
                                        fi                                0.000                                                                                                                                       fi                0.200
                                           1                                                                                                                                                                         1
                                            I10                            70.2 mm/hr                                                                                                                                 I10                70.2 mm/hr
                                           C10                             0.70                                                                                                                                      C10                 0.74

AEP                                                 Fy                            Cy                      Iy (2100)                        Qy (m3/s)                   AEP                                                  Fy                  Cy            Iy (2100)       Qy (m3/s)
                                   63.2% AEP                                0.8                   0.560                            97.87                      0.0990                                          63.2% AEP                   0.8         0.592            139.20         0.0366
                                    50% AEP                                0.85                   0.595                           110.40                      0.1186                                           50% AEP                   0.85         0.629            157.20         0.0439
                                    20% AEP                                0.95                   0.665                           148.56                      0.1784                                           20% AEP                   0.95         0.703            212.40         0.0664
                                    10% AEP                                   1                   0.700                           173.04                      0.2187                                           10% AEP                      1         0.740            249.60         0.0821
                                      5% AEP                               1.05                   0.735                           196.56                      0.2609                                             5% AEP                  1.05         0.777            284.40         0.0982
                                      2% AEP                               1.15                   0.805                           225.84                      0.3283                                             2% AEP                  1.15         0.851            328.80         0.1244
                                      1% AEP                                1.2                   0.840                           246.96                      0.3746                                             1% AEP                   1.2         0.888            362.40         0.1430


Channel Sizing
Using Manning's Eqn - V = R 2/3. Sf1/2/n

                                            D                                0.6 m                                                                                                                                    D                  0.45 m
                                              r                              0.3 m                                                                                                                                      r               0.225 m
                                             n                            0.013                                                                                                                                        n                0.013
                                      Sf (min)                            0.015 m/m                                                                                                                             Sf (min)                0.010 m/m
                                             A                            0.141 m²                                                                                                                                     A                0.080 m²
                                             P                            0.942 m                                                                                                                                      P                0.707 m
                                             R                            0.150 m                                                                                                                                      R                0.113 m
                                             V                            2.660 m/s                                                                                                                                    V                1.793 m/s
                                      QCapacity                           0.376 >=                                                  0.37               TRUE                                                     QCapacity               0.143 >=                       0.143      TRUE