RFI - Attachment F - Engineering Report

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


                4. CONCLUSION




                The main findings from the testing programme are:


                •    The reinforcing bar placed across the inlet had little effect on
                     hydraulic capture for on-grade tests. 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 with no
                     pollution and up to 120mm greater with pollution. A build up of
                     pollution on the grate, restricted by the bar, caused ‘jetting’ of water
                     above the kerb.
                •    The crate basket was ineffective in retaining pollution above a flow
                     rate of 25 L/sec for on-grade testing. Nearly all (90%) of pollution
                     added to the gutter after the basket had become blocked bypassed the
                     basket. After an approach flow of 320 L/sec only 2% of pollution
                     was retained for all longitudinal slopes.             The basket was more
                     effective in retaining pollution under sag conditions.
                •    The mesh pit insert was inefficient in retaining pollution above a flow
                     rate of 25 L/sec.       Only 5% of the pollution was retained at an
                     approach flow of 25 L/sec for the 1% and 4% longitudinal slope.
                     10% was retained for the 12% grade however all pollution had
                     bypassed the pit at an approach flow greater than 60 L/sec for all
                     slopes.
                •    The Enviropod basket was capable collecting and retaining large
                     amounts of pollution and had no significant effect on the hydraulic
                     performance of the gully pit. The basket retained up to 70% of
                     pollution added after an approach flow of 320 L/sec. At 12% grade,
                     litter was trapped in the overflow outlet, reducing the capture
                     capacity of the gully pit. This could also occur for flatter grades and
                     high approach flows.         Initial testing of the basket led to some
                     modifications to increase support under high approach flows used in
                     the testing programme.

                Urban Water Resources Centre              20             University of South Australia