RFI - Attachment F - Engineering Report

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

                SUMMARY



                Stormwater pollution control is usually managed near source or at the
                end of a drainage system. The Brisbane City Council and Gold Coast
                City Council are currently investigating several options of managing
                stormwater litter at the source utilising their Lip-in-Line Gully Pit (small
                lintel).
                A range of devices are currently available to collect litter using the gully
                pit, however there is limited information regarding;
                •    The effect on the inlet hydraulic capture performance, and
                •    the effectiveness of litter capture.


                Four litter control systems were evaluated for both on-grade and sag
                conditions with varying approach flows up to 320 L/sec. Test results and
                observations included:


                •    The horizontal bar placed across the inlet had little effect on
                     hydraulic capture for on-grade slopes. However for sag conditions
                     and at flows above 200 L/sec, the hydraulic capture capacity was
                     reduced. Depths at invert were up to 50mm greater for the case
                     without litter and up to 120mm greater with litter.
                •    Both the mesh and tray basket inserts were ineffective in collecting
                     and retaining litter. Both systems had no significant effect on the
                     hydraulic capture capacity of the gully pit.
                •    The Enviropod basket is capable of collecting and retaining
                     considerable amounts of pollution at flow rates up to 320 L/sec.
                     Resuspension of pollution occurred at flows above 100 L/sec,
                     however the unit still retained up to 70% of pollution at 1%
                     longitudinal slope at an approach flow of 320 L/sec. The Enviropod
                     basket affected the hydraulic capture capacity of the gully pit at 12%
                     grade due to blockage caused by litter trapped in the overflow outlet.




                Urban Water Resources Centre               3             University of South Australia