RFI - Sediment basin calculations

SWMP Commentary, Detailed Calculations

2. Storm Flow Calculations
Peak flow is given by the Rational Formula:

                             Qy = 0.00278 x C10 x FY x Iy, tc x A

                where:     Qy       is peak flow rate (m 3/sec) of average recurrence interval (ARI) of "Y" years
                           C10      is the runoff coefficient (dimensionless) for ARI of 10 years. Rural runoff
                                    coefficients are given in Volume 2, figure 5 of Pilgrim (1998), while urban
                                    runoff coefficients are given in Volume 1, Book VIII, figure 1.13 of Pilgrim
                                    (1998) and construction runoff coefficients are given in Appendix F
                            Fy      is a frequency factor for "Y" years. Rural values are given in Volume 1,
                                    Book IV, Table 1.1 of Pilgrim (1998) while urban coefficients are given in
                                    Volume 1, Book VIII, Table 1.6 of Pilgrim (1998)
                            A       is the catchment area in hectares (ha)
                           Iy, tc   is the average rainfall intensity (mm/hr) for an ARI of "Y" years
                                    and a design duration of "tc" (minutes or hours)

    Time of concentration (tc) = (107 n L0.333) / S0.2, in minutes - Friends Equation
                                 or use table of standard inlet times (QUDM Table 4.06.1)
                     where:      n is Hortons roughness value for the surface (similar to Mannings value)
                                 L is length of flow path in metres
                                 S is slope in %

                 n= 0.0275                   L=    50    m                          S=      5.5       %
    Time of concentration (tc) =              8     mins
Peak flow calculations, 1
                 A          tc                              Rainfall intensity, I, mm/hr
    Site                                                                                                                  C10
                (ha)      (mins)       1 yr,tc    5 yr,tc       10 yr,tc      20 yr,tc     50 yr,tc       100 yr,tc
     1          1.136       10         97.5        148           172           196          225             247           0.9




Peak flow calculations, 2
                                                       Peak flows
              Frequency
    ARI
                factor      1                                                                                   Comment
   (yrs)
                 (Fy)
                          (m3/s)      (m3/s)      (m3/s)        (m3/s)       (m3/s)        (m3/s)
   1 yr,tc       0.8      0.222
   5 yr,tc      0.95      0.400
   10 yr,tc       1       0.489
   20 yr,tc     1.05      0.585
   50 yr,tc     1.15      0.735
  100 yr,tc      1.2      0.842




QLD - Sediment Basins- V2.xls                                                                                                   2