Civil Response

83 Butler St, Tewantin QLD 4565
Rational Method Calculations
File: 9279
Date: 06/05/22

Stormwater Drainage Runoff - Calculations    Unit                               Value                              Reference / Comments
Existing condition

Average Recurrence Interval (ARI)            Years      2        5       10              20       50       100
Area                                          ha      0.107    0.107    0.107           0.107    0.107    0.107    Existing predeveloped lot catchment to west
fi                                                    0.250    0.250    0.250           0.250    0.250    0.250
C10                                                    0.75     0.75     0.75            0.75     0.75     0.75    QUDM Table 4.5.3
Fy                                                     0.85     0.95      1              1.05     1.15     1.2     QUDM Table 4.5.2
Cy = Fy * C10                                         0.6375   0.7125    0.75           0.7875   0.8625    0.9
Time of concentration (tc)                  minutes     5        5        5               5        5        5      QUDM Table 4.6.3 residential
Rainfall Intensity (I)                      mm / hr    163      201      223             253      292     322.0
Qpost (Peak Runoff) = (C*I*A)/360            m3 / s   0.031    0.043    0.050           0.059    0.075    0.086

Stormwater Drainage Runoff - Calculations    Unit                               Value                              Reference / Comments
Developed Condition

Average Recurrence Interval (ARI)            Years       2        5       10              20       50      100
Area                                          ha      0.0744   0.0744   0.0744          0.0744   0.0744   0.0744   Post development Lot 4
                                                                                                                   QUDM table 4.5.1 - Urban residential - lot density excluding
fi                                                    0.750    0.750    0.750           0.750    0.750    0.750    roads (max value in range given in table.)
C10                                                    0.83     0.83     0.83            0.83     0.83     0.83    QUDM Table 4.5.3
Fy                                                     0.85     0.95      1              1.05     1.15     1.2     QUDM Table 4.5.2
Cy = Fy * C10                                         0.7055   0.7885    0.83           0.8715   0.9545   0.996
Time of concentration (tc)                  minutes     5        5        5               5        5        5      QUDM Table 4.6.3 residential
Rainfall Intensity (I)                      mm / hr    163      201      223             253      292     322.0
Qpost (Peak Runoff) = (C*I*A)/360            m3 / s   0.024    0.033    0.038           0.046    0.058    0.066