Minnegang Creek Flood Study Report - Wollongong City Council

Figure 5-6.Table 6-2 Piped drainage system capacitiesPipe branch Pipe Diameter (m) Capacity (m 3 /s) Capacity in ARIPipe 1 0.450 0.6 2 yearsPipe 1 0.600 1.4 2 yearsPipe 1 0.900 0.9 1 yearPipe 1 1.350 3.7 1 yearPipe 2 0.450 0.6 2 yearsPipe 3 0.375 0.4 1 yearPipe 4 0.375 0.6 100 yearsPipe 5 0.375 0.5 5 yearsPipe 6 0.375 0.04 1 yearPipe 7 0.375 0.1 50 yearsPipe 8 0.375 1.0 2 yearsPipe 8 0.600 0.6 2 yearsPipe 8 0.675 1.8 5 yearsPipe 9 0.375 0.7 20 yearsPipe 10 1.200 1.6 1 yearPipe 11 0.375 0.5 5 yearsPipe 12 0.375 0.3 1 yearPipe 13 0.375 0.3 2 yearsPipe 14 0.375 0.05 1 yearPipe 15 0.375 0.3 100 yearsPipe 16 0.375 0.3 20 yearsIn some locations, surcharging of the system occurs due to the close proximity of thepipe obvert to the surface level and the high pit losses occurring at these manholes.This results in a reduced capacity for this section of the system.Even for events with small return periods, the capacities of the minor branches of thesystem are limited by small pipe diameters and by the very low grades at which thepipes are laid.6.3 CULVERT STRUCTURESTable 6-3 lists the culvert structures through which Minnegang Creek passes.Table 6-3 Culvert structuresCulvert location Structure details U/S invertlevel (m)D/S invertlevel (m)Length(m)U/S weirlevel (m)Lake HeightsRoadNorthcliffeDriveIllawarra YachtClub carpark1200 mm diameter RCP 26.82 26.18 21.8 29.43-cell box culvert(1.9m x 1.25m / 1.8m x1.25m / 1.9m x 1.25m)0.65 0.47 19 2.102 x 1650mm diameter RCP 0.48 0.43 7.3 2.45SV8507-D0-001 Rev 2 6-5218/10/02