RFI - Attachment F - Engineering Report

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

                4% longitudinal slope:
                •    At an approach flow of 200L/sec, the water level in the basket was
                     higher (100mm below invert) for the finer meshed basket than the
                     coarse mesh (200mm below invert). The higher water level in the pit
                     can be attributed to the reduced size in mesh of the basket.
                •    Both baskets retained 55% of debris after an approach flow of 320
                     L/sec.


                12% longitudinal slope:
                •    The water level in the pit rose above the overflow level at 100L/sec
                     therefore resulting in small losses.
                •    After 320L/sec the coarse mesh basket retained 65% of debris while
                     the fine meshed basket retained 60%.


                Sag


                For the sag test, the basket was bisected in half to simulate flow
                approaching from opposite directions. 20L of litter was used for the sag
                litter tests because of the high capture capacity of the basket before
                bypass. The following observations were made:
                •    With the coarse mesh the basket retained 50% of the 20L of litter
                     after being subjected to an approach flow of 340L/sec. The bag
                     became considerably coated with larger sized litter (mostly organics).
                •    With the fine mesh, only 10% of the 20L was retained after an
                     approach flow of 360L/sec (equivalent). The finer mesh experienced
                     less coating on the sides of the basket. It was observed that the flow
                     into the basket had the effect of ‘washing off’ some of the litter
                     attached to the sides and therefore allowing litter to bypass the basket
                     at higher flows.




                Urban Water Resources Centre              16             University of South Australia