Original Application Part 8 - Stormwater Details [As Published] · 132008.1787

Detention tank design
From Urban Road design Manual Vol (10-7080)
For small catchments hydrograph may be approximated as folls:-
      Use triangular shape with duration                                        = 2.67 x Time of Concentration
      Actual catchment area entering tank from proposed site                                   2124 sq.m.             roof+terraces
      Pipe rainfall design intensity entering tank Q20                          =               252 mm/hr
      Weighted Coeff of runoff                                                  =               0.95
      Peak Flow entering tank                                                   = C * I * A / 3600
      Therefore Peak Flow entering tank                                         =             141.2 Litres/sec
      (Note: Pipes entering the tank are designed for the above intensity. All flows in excess of this will be bypassed to O'Land Flow
      or other pipework)
      (However it is still necessary to produce the required reduction in peak flow for the maximum event shown above)

Outflow Hydrograph (from storage device)
                    Soil Permeability                                         =                0       m/day
                                                                              =            0.000       mm/sec
                       Absorption Area                                        =                0        sq.m
                       Therefore absorption                                   =            0.000        L/sec
      Outlet Device
                      O'Flow device weir/pipe (W/P)                           =                 p
                      Outlet Pipe dia                                         =              175         mm         for calcs only
                      Outlet Pipe length                                      =               10         m
                      Outlet Pipe grade 1:?                                   =              200
                  Try Storage Length                                          =                 3        m.         equivalent
                      Storage width                                           =             6000 mm                 tank size
      Available storage depth below Pipe outlet IL                            =               0.0 mm

            Therefore Storage Vol below o'flow device                         =                 0       Litres
                      (includes vol stored in absorption trench)
                      Storage Area above O'Flow                               =               18        Sq.m.
                      Void Ratio                                              =                1

RESULTS
      Max Inflow   =        141.2         (L/sec)            Max depth over weir/oflow IL               1310        (mm)
      Max Outflow =          72.6         (L/sec)            Area of storage above weir/Oflow IL         18         sq.m
      Reduction    =         68.7         (L/sec)            Therefore Vol aboveOFlow IL                23.58       cu.m
 Required Reduction=         52.2         (L/sec)            Vol below oflow IL (from above)             0.0        cu.m
                         Therefore OK                        Therefore Total storage vol.               23.58       cu.m
                                                             therefore Total Storage depth              1310        mm