RFI - Attachment F - Engineering Report

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

                                          200




                                          160




                                          120




                   Depth at Invert (mm)
                                          80

                                                                                                                     fine mesh no pollution

                                                                                                                     fine mesh with pollution

                                          40                                                                         coarse mesh with pollution

                                                                                                                     coarse mesh no pollution

                                                                                                                     standard inlet

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




                                                         Figure 9: Sag test results (depth at invert)
                Discussion of results


                Both baskets were effective in capturing and retaining a large proportion
                of litter at flows up to 100L/sec. At 1% longitudinal slope the fine mesh
                basket was slightly better in capture performance, whilst at the 12% slope
                the coarse mesh basket was slightly better.
                The fine mesh basket resulted in lower depths at invert at the same
                approach flow than for the coarse mesh basket.                                                 This is due to the
                resuspension of litter in the basket at high approach flows. Only 10% of
                the 20L of litter added to the fine mesh basket was retained, where as
                50% was retained by the coarse mesh basket.


                3.5 Chamber Water Level Pre-testing


                Testing was carried out to determine the effects on inlet capture as a
                result of high chamber water level. Tests were conducted for the 1, 4 and
                12% longitudinal grades.                              It was observed that with the short lintel
                (2.4m) a high CWL of 150mm below the gutter invert did not affect the
                capture performance.




                Urban Water Resources Centre                                   19                        University of South Australia