Eastwood & Terrys Creek Floodplain Risk Management Study & Plan Flood Study Report

The study area includes that portion of Terrys Creek within the City of Ryde from Terry\r\nRoad to the creek’s confluence with the Lane Cove River. In addition, as shown in\r\nFigure 1, it includes all significant tributaries of Terrys Creek.\r\n\r\nThis report provides a description of the establishment and calibration of a computer\r\nmodel of flood behaviour throughout the study area. This model will become the\r\nprimary tool for assessing both the existing flood behaviour and the changes which may\r\noccur through the implementation of any flood mitigation options that may be proposed\r\nduring the course of the study.\r\n\r\n#Catchment Areas\r\nFor the purposes of Council’s management of the stormwater systems within the City of\r\nRyde, the Terrys Creek catchment has been traditionally divided into the Eastwood and\r\nTerrys Creek drainage subcatchments.\r\n\r\nThe Ryde component of the Eastwood subcatchment is about 169 hectares in area and\r\nextends from the intersection of Marsden Road and Terry Road to Blaxland Rd,\r\nEastwood. The Terrys Creek subcatchment comprises an area of about 326 hectares\r\nand extends from the intersection of Blaxland Road and Kings Road to the Lane Cove\r\nRiver.\r\n\r\nThe upstream portion of Terrys Creek (within Parramatta City Council) has an\r\nestimated area of 160 hectares, while the remaining portion of the catchment (within\r\nHornsby Shire Council) has an estimated area of 357 hectares. The estimated total\r\narea of Terrys Creek is therefore approximately 1012 hectares.\r\n\r\nThe Eastwood town centre is located within the Eastwood subcatchment, and straddles\r\nthe Main Northern Railway Line (Figures 1 and 2). The railway embankment divides\r\nthe Eastwood town centre into eastern and western halves.\r\n\r\n#Models\r\nThe DRAINS software has been used to model the hydrologic regime of the Terrys\r\nCreek catchment to its confluence with the Lane Cove River (see Figure 2).\r\nDRAINS is a comprehensive hydrologic modelling program for designing and analysing\r\nvarious types of catchments and urban stormwater drainage systems. It also includes\r\nsome hydraulic modelling capabilities for pipes and overland flowpaths. It was first\r\nreleased in January 1998 and is marketed by Watercom Pty Ltd. The software is widely\r\nused in Australia and Council itself has used DRAINS for many years.\r\n\r\nFollowing various discussions with Council officers, the widely used and Australian\r\ndeveloped TUFLOW model (Reference 9) was chosen as the principal hydraulic\r\nmodelling tool for use in the study.\r\nThere were seen to be numerous advantages of using a sophisticated two-dimensional\r\n(2D) model such as TUFLOW for simulating flood conditions within Terrys Creek and its\r\ntributaries. These advantages included not only the model’s ability to simulate flood\r\nflows along a complicated network of overland flowpaths such as occurs in the study\r\narea, but also the ability of the model to produce figures to aid community\r\nunderstanding and acceptance of the flood study results.\r\nThe technical description of the TUFLOW model and its specific application to Terrys\r\nCreek is provided in Appendix B.