RFI - Attachment F - Engineering Report

Inversely there were a greater percentage of coarse or gross particles higher in the
catchment. This suggests the large particles are not as easily transported overland
because of the greater mass. The percentage of bed load in the bed load did not seem
vary with topography.

This observation has considerable stormwater management implications as finer particles
are generally thought to have higher concentrations of contaminants which are more bio-
available and further investigation into the overland transportation of particles could be
carried out.

Figure 9 shows the average composition of the material retained across the catchment by
the Enviropod. As can be seen the majority of the material caught in the Enviropod can
be classified as suspended solids.

Only 12 % of the material caught in the Enviropod is gross pollutants. This has
significant management implications for stormwater treatment devices within Ku-ring-
gai, as removal of gross pollutants alone will result in the majority of the contaminants
entering the receiving environment.

32% of the material caught in the Enviropods can be classified as bed load. Bed load is
not usually considered when determining pollution loads in stormwater; however it is
obviously a large percentage of the material being transported into the stormwater
reticulation.


            Average Composition of Material Removed by the
                  Enviropods From Blackbutt Creek


                      12%

                                                              Suspended Solids ( <1.08 mm)

                                                              Bed Load (1.08mm<X>4.75mm)


             32%                                              Gross Pollutants ( >4.75mm)
                                              56%




                        Figure 9: Average Composition all Enviropods




                                            16