Minnegang Creek Flood Study Report - Wollongong City Council

The hydraulic characteristics of each flow path are represented by cross sections andstructures located along each branch in the model.5.4.2 Cross sectionsCross sections through the overland flow system within the Minnegang Creekcatchment were generally in the form of survey strings created by G.A. GoodmanSurveys in accordance with survey briefs provided to Council by Halliburton KBR.This meant that cross sections did not have to be extracted from existing contour data,thus increasing the level of detail of the model.Cross sections within Barina Park were extracted from a full detailed survey of thepark performed by G.A. Goodman Surveys as part of the July 2000 survey. Crosssection locations were determined such that the full extents of the park and variation innatural surface levels were incorporated into the cross sections. This ensured the mostaccurate representation of the detention storage available within the park in the MIKE11 model.Cross sections along the section of piped drainage system are located at manholesconnecting the lengths of pipe. These manholes include gully pits, grated inlet pits,junction pits and headwalls. Invert levels and surface (overflow) levels for eachmanhole were obtained primarily from the January 2001 survey of the catchment.Identification of cross sections in the model is done by way of assigning a chainagecorresponding to the location of a cross section along the branch. Typically, theupstream cross section on a branch was set to Chainage 0.000 (in kilometres), withchainages increasing downstream. Chainages assigned along weir branches were setto the corresponding cross section chainages on the main branch where the weirbranch splits and then rejoins.5.4.3 StructuresCulvertsCulvert details for the Minnegang Creek crossings under Lake Heights Road andNorthcliffe Drive, specifically culvert sizes, lengths and invert levels, were sourcedfrom the two surveys of the catchment. A third culvert, located underneath a carparkaccess road adjacent to the Lake Illawarra Yacht Club, was also incorporated into themodel. The stage/discharge relationship for each culvert is automatically calculatedby MIKE 11 based on the geometry of the culvert and the adjacent cross sections.WeirsCross sections with the potential to act as weirs were identified from a field inspectionby Halliburton KBR carried out in July 2000 and entered into th e MIKE 11 model asbroad-crested weirs. Weir locations generally consist of cross sections along aroadway crown that effectively form a control point for flow, ponding water on oneside of the road until the weir level is exceeded. A weir was also located along theembankment crest of the Barina Park detention basin, which forms the high leveloutlet for the basin. All weirs used in the model were defined as broad-crested weirsand their hydraulic characteristics described in terms of a stage/flow -widthSV8507-D0-001 Rev 2 5-1918/10/02