RFI - Attachment F - Engineering Report

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

                •    At 1% and 4% grades, the fine mesh basket (with litter) captured up
                     to 5L/sec more than the coarse mesh basket at an approach flow of
                     320L/sec.


                •    At 12% longitudinal slope, the coarse mesh basket captured up to
                     11L/sec more than the fine mesh basket at an approach flow of
                     200L/sec and 8L/sec more with an approach flow of 320L/sec.


                Sag


                Four sag tests to determine hydraulic performance of the inlet were
                conducted; two with fine mesh (with and without litter) and two with the
                coarse mesh (with and without litter). This enabled a comparison of
                performance between the two baskets under empty and blocked
                conditions. The results were also compared to sag capture results with no
                basket. Pond depth at invert versus approach flow characteristics are
                provided in Figure 9.


                Fine mesh sag test


                At low to medium approach flows (up to 200L/sec) the addition of litter
                reduced the capture capacity of the inlet, increasing the pond depth at
                invert by up to 15mm. However at flows above 200L/sec there was no
                difference in flow pond depth at invert for the case of with and without
                litter.


                Coarse mesh sag test


                The effect of the coarse mesh was to increase the flow pond depth at
                invert by up to 15mm at flows below 200L/sec, as for the fine mesh.
                However the coarse mesh (with litter) showed similar flow pond depths
                to the fine mesh (without litter) up to 200L/sec.
                The results from the sag test are presented in figure 9 below.



                Urban Water Resources Centre              18             University of South Australia