Erosion and Sediment control checklist and calcs · OPW19/0098

4. Volume of Sediment Basins, Type D and Type F Soils
               Basin volume = settling zone volume + sediment storage zone volume

Settling Zone Volume
The settling zone volume for Type F and Type D soils is calculated to provide capacity to contain all
runoff expected from up to the y-percentile rainfall event. The volume of the basin's settling zone (V) can
be determined as a function of the basin's surface area and depth to allow for particles to settle and can
be determined by the following equation:

                                V = 10 x Cv x A x Rx-day, y-%ile (m3)

                         where:

                               10 = a unit conversion factor

                               Cv = the volumetric runoff coefficient defined
                                    as that portion of rainfall that runs off as
                                    stormwater over the x-day period

                     Rx-day, y-%ile = is the x-day total rainfall depth (mm) that
                                      is not exceeded in y percent of rainfall
                                      events. (See Sections 6.3.4(d), (e), (f),
                                      (g) and (h)).

                                  A = total catchment area (ha)

Sediment Storage Zone Volume
In the detailed calculation on Soil Loss Classes 1 to 4 lands, the sediment storage zone can be taken as
50 percent of the settling zone capacity. Alternately designers can design the zone to store the 2-month
soil loss as calculated by the RUSLE (Chapter 6.5.3(d). However, on Soil Loss Classes 5, 6 and 7 lands,
the zone must contain the 2-month soil loss as calculated by the RUSLE (Chapter 6.5.3(d).


Place an "X" in the box below to show the sediment storage zone design parameters used here:
                      50% of settling zone capacity,
               x      2 months soil loss calculated by RUSLE


.                                                                   Average Depth of basin =    0.25    metres

                                            Total    Settling   Sediment    Total            Basin shape
                                         catchment    zone       storage    basin
     Site     Cv        Rx-day, y-%ile
                                            area     volume      volume    volume    L:W       Length      Width
                                            (ha)      (m3)         (m3)      (m3)    Ratio       (m)        (m)

    Basin 1   0.54           54            0.873       255         15       270        3        56.9       19.0
              0.54                                                                     3
              0.54                                                                     3
              0.54                                                                     3
                                                                                       3
                                                                                       3