RFI - Attachment F - Engineering Report

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

                                         all litter had passed through the chamber except for an aluminium
                                         can.


                Hydraulic performance.


                On-grade:
                The mesh insert did not significantly effect the hydraulic capture
                performance of the gully pit for all longitudinal slopes.


                Sag:
                At 0% (sag) longitudinal slope, the mesh insert caused the inlet to reach
                ‘orifice’ condition sooner (ie. at a smaller approach flow).


                                         200


                                         180


                                         160


                                         140


                                         120
                  Depth at Invert (mm)




                                         100


                                         80


                                         60
                                                                                                                         meshed pit

                                         40

                                                                                                                         standard pit
                                         20


                                          0
                                               0   50    100    150    200          250            300      350    400          450     500
                                                                             Approach Flow (L/s)




                                                   Figure 4: Sag “0” Grate results – meshed pit insert


                Discussion:
                From the observations above, the ‘blocked’ meshed insert had no
                significant effect on the hydraulic capture performance (on-grade) of the
                inlet. All floatable litter passed through the chamber at 25L/sec and
                semi-buoyant litter was remobilised at flows greater than 25L/sec.
                For the sag condition, the insert affected the hydraulic capture between
                150-340L/sec. Above 340L/sec it would appear that the capture (orifice)
                was controlled by the inlet opening.


                Urban Water Resources Centre                                   11                        University of South Australia