Minnegang Creek Flood Study Report - Wollongong City Council

flows for the full range of storm frequencies. The modelling of the piped drainagesystem is discussed further in Section 5.12.5.3 EXTENT OF MODELLINGAlthough the RAFTS model was required to cover the entire catchment areacontributing to generation of runoff, the extent of the MIKE 11 model was limited tothose areas requiring detailed investigation as part of the study, including:• Minnegang Creek, from its headwaters upstream of Ranchby Avenue to LakeIllawarra;• The tributary from Gordon Crescent, under Ranchby Avenue and confluencingimmediately upstream of Lake Heights Road;• The tributary from Melinda Grove, under Gilgandra Street and confluencing at thesouthern end of Barina Park;• The three minor branches draining the undeveloped area between Ranchby Avenueand Hilltop Avenue; and• The minor branch draining the area between Canberra Road and Minnegang Creek.In addition to these overland flow paths, two branches of the catchment’s pipeddrainage system were also incorporated into the MIKE 11 model. The first branchruns from the grated inlet pit at the southern end of Barina Park, under MirrabookaRoad and discharges into Minnegang Creek at an outlet downstream of WeringaAvenue. Since this grated inlet pit forms the low -level outlet to the existing detentionbasin in Barina Park, the incorporation of this reach of pipe was necessary so that theoutlet behaviour of the basin could be adequately simulated. The second branchconveys a section of Minnegang Creek from the eastern end of the vacant lot betweenLake Heights Road and Barina Avenue, linking into the first piped drainage branchapproximately 20m downstream of the grated inlet pit in Barina Park.5.4 MODEL CONSTRUCTIONA total of 20 river branches, 137 cross sections, 14 culverts and 14 weirs were used inthe MIKE 11 model to describe the topography of the catchment and existingstructures to a suitable level of detail.Figure 5-1 shows the construction of the MIKE 11 model that represents thecatchment in its existing condition. A full listing of river branches, cross sections,culverts and weirs used in the MIKE 11 model is provided in Appendix E.5.4.1 River branchesRiver branches are used to define the various flow paths in the model. For this study,branches describe three main types of flow path:• overland flow paths• weir flow over roadways with a culvert crossing• a branch of the piped drainage system.The river branches used are listed in Table 5-1.SV8507-D0-001 Rev 2 5-1618/10/02