RFI - Attachment F - Engineering Report

                           Month                         Sub-Catchment
                                                   Urban   Comm. Base
                             April                    41%     28%      25%
                             June                     31%     25%      27%
                             August                   25%     42%      31%
                             October                  42%     24%      26%
                             December                 27%     41%      46%
                             Weighted Average         35%     31%      29%
                    Table 3: Percentage of above 1180 micron and below 4.75mm (bed Load)
                           Month                         Sub-Catchment
                                                    Urban Comm. Base
                            April                     5%     17%       7%
                            June                      5%      9%       7%
                            August                    9%     13%       8%
                            October                  10%     27%       8%
                            December                 28%     26%       7%
                            Weighted averages        11%     18%       7%

                             Table 4 Percentage above 4.75mm (Gross Pollutants)



                               Particle Size Distribution vs. Land Use


              70%
              60%                                                       Suspended Solids ( <1.08 mm)
              50%
  % of Load




              40%
                                                                        Bed Load (1.08mm<X>4.75mm)
              30%
              20%
              10%                                                       Gross Pollutants ( >4.75mm)

              0%
                       Comm.           Urban           Base
                                    Land Use



                               Figure 8: Particle Size Distribution vs. Land Use
The data presented above indicate that material collected in the Enviropod units in each
of the areas tends to have a finer composition further down the catchment. Finer
particles are more easily mobilised by water and wind. Larger particles also settle out
easier as velocities lower. As flow reaches the base of the hill, the grade levels and flows
tend to lower. This causes large particles to settle. The settling would also occur as a
storm’s intensity subsides or if there was a change in surface.


                                                      15