RFI - Attachment F - Engineering Report

Evaluation of Gully Pit Inlet Litter Control Systems– Brisbane City Council and Gold Coast City Council

                                           250


                                                                                             bar with debris
                                                                                                                           bar no debris

                                                                                                                                      no bar
                                           200




                    Depth at Invert (mm)
                                           150




                                           100




                                           50




                                            0
                                                 0   50         100     150           200              250           300           350         400
                                                                              Approach Flow (L/s)




                                                          Figure 3: “Sag” Reinforcing Bar “0” Grate.


                3.2 “Meshed” pit insert.


                The meshed pit inlet configuration (see Appendix A) was modified to
                simulate fully blocked conditions. For this reason, a steel plate was used
                instead of mesh.


                Test results and observations:


                Observations from the testing were:


                Litter capture performance.
                •                          At 1% and 4% slope, all litter was captured by the inlet (at 25L/sec),
                                           however only 5% of the 10L of litter was retained by the insert for
                                           both longitudinal slopes. This litter was resuspended and passed
                                           through the inlet when flow was increased to 60L/sec.
                •                          At 12% slope and approach flow of 25L/sec, 10% of the 10L of litter
                                           was retained in the inlet box. This material was mostly semi-buoyant
                                           litter (wet leaves) which either sank to the bottom or remained in
                                           suspension. The grate captured a small proportion of litter. However
                                           when the test was repeated at 25L/sec remobilisation of the captured
                                           material in the inlet occurred and only 5% was retained. At 60L/sec


                Urban Water Resources Centre                                     10                            University of South Australia