RFI - Sediment basin calculations

SWMP Commentary, Detailed Calculations

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 (m 3)

                         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:
               x     50% of settling zone capacity,
                     2 months soil loss calculated by RUSLE


.                                                                   Average Depth of basin =     1      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)        3
                                                                             (m )    Ratio      (m)         (m)

     1        0.58          34.6           1.136       228        114       342        3        32.0       10.7
              0.58                                                                     3
              0.58                                                                     3
                                                                                       3
                                                                                       3
                                                                                       3




QLD - Sediment Basins- V2.xls                                                                                      5