RFI - Attachment F - Engineering Report

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



                Discussion:
                For the 1% longitudinal slope, 76% of the litter was retained at an
                approach flow of 320L/sec (see Figure 1). The remaining 24% passed
                through the inlet beneath the bar or bypassed the inlet. The high capture
                efficiency is due to the lower approach flow velocities at flatter grades.
                The majority of litter retained in front of the bar was plastic bottles and
                milk cartons.
                At the steep (12%) slope the inlet retained 30% of litter at an approach
                flow of 60L/sec. The high velocity forced the majority of litter past the
                inlet. At an approach flow of 320L/s only a plastic bag remained stuck
                on the grate.




                          Figure 1: Pollution remaining after 320L/sec at 1% slope.


                The horizontal bar caused a build up of litter at the downstream end of
                the inlet. Water was observed ‘jetting’ over the downstream transition,
                due to the litter caught, at higher approach flows and more significantly
                at steeper slopes (see Figure 2).




                Urban Water Resources Centre               8             University of South Australia