Clarence Town - Flood Study Inc Appendix and Figures

The objective of the study was to undertake a detailed flood study of the Clarence Town catchment\r\nand establish models as necessary for accurate flood level prediction. Central to this was the\r\ndevelopment of a two-dimensional hydraulic model of the floodplain.\r\nIn completing the flood study, the following activities were undertaken:\r\n• Collation of database of historical flood information for the Clarence Town catchment;\r\n• Acquisition of topographical data for the catchment including cross section and hydraulic\r\nstructure survey;\r\n• Consultation with the community to acquire historical flood information and liaison in regard to\r\nflooding concerns/perceptions and future floodplain management activities;\r\n• Development of a hydraulic model (using TUFLOW software) to simulate flood behaviour in the\r\ncatchment;\r\n• Calibration of the developed models using the June 2007, February 2009 and February 2011\r\nflood events;\r\n• Prediction of design flood conditions in the catchment using the calibrated models; and\r\n• Production of design flood mapping series.\r\nA good model calibration and validation was achieved with the available data, confirming the\r\nappropriateness of the model for design flood simulation.\r\nThe local catchment flooding is typically characterised by a series of well-defined overland flow paths\r\nthat feed the main Town Creek channel prior to discharge to the Williams River. Given the relatively\r\nsmall size of the contributing catchments, extensive flood inundation of property is somewhat limited.\r\nOnly three existing properties (all commercial premises) have been identified as at potential risk of\r\nabove floor flooding for events up to the 1% AEP flood magnitude.\r\nThe majority of the natural flood flow paths are through private land. In most part, development on\r\nthese lots has been located a sufficient distance from the natural drainage lines to limit potential for\r\nbuilding inundation.\r\nThe lower reaches of the Town Creek catchment are dominated by Williams River flooding. Typically\r\ndownstream of approximately the IGA culvert, the Williams River 1% AEP design flood results in\r\nhigher flood conditions than corresponding 1% AEP local catchment event. Accordingly, the Williams\r\nRiver design flood conditions established by BMT WBM (2009) should be applied for future flood\r\nplanning and development control in these lower reaches.