Under the NSW Government's flood prone land policy the City is required to manage flooding issues and put plans into place to safeguard flood-prone areas. The local area has been divided into 9 catchments covering 2,666ha. More information on floodplain management catchments

This Floodplain Risk Management Study investigates what can be done to reduce or manage the effects of flooding in the catchment. The Floodplain Risk Management Plan recommends a mix of strategies to manage the risks of flooding. Using the merits-based approach advocated in the NSW State Government’s Floodplain Development Manual (2005) and in consultation with the community, Council and state agency stakeholders, a number of potential options for the management of flooding were identified. These options included: • flood modification measures; • property modification measures; and • emergency response measures. An extensive list of options was assessed against a range of criteria (technical, economic, environmental and social). Hydraulic modelling of some of the flood modification options was undertaken to provide a comprehensive analysis of those options that would involve significant capital expenditure.

Revision I (May 2022).

Complete report

Complete report

The Green Square Floodplain Risk Management Plan has been prepared in accordance with the NSW Floodplain Development Manual (April 2005) and: Is based on a comprehensive and detailed evaluation of all factors that affect and are affected by the use of flood prone land; Represents the considered opinion of the local community on how to best manage its flood risk and its flood prone land; Provides a long-term path for the future development of the community. All possible management measures were evaluated in the Floodplain Risk Management Study (Reference 5) taking into account a range of parameters. This process eliminated a number of measures including:,

The Rouse Hill Development Area (RHDA) straddles the boundary of Blacktown City Council and The Hills Shire Council. Urban development of this area prompted the need to regulate development to reduce the impact of flooding and flood liability. Sydney Water is designated as the Acquisition Authority for land that is identified for Trunk Drainage purposes within the RHDA. As urbanisation and development continues, the ability to effectively manage flood prone land within the RHDA will be dependent on an accurate assessment of existing flooding conditions upon which to base future floodplain management decisions. Sydney Water engaged WMAwater to undertake the Rouse Hill Flood Study to address these issues, resulting in this 2014 Flood Study Report.

SOBEK

In accordance with NSW Government policy, the Council of the City of Ryde is committed to preparing a Floodplain Risk Management Plan for Macquarie Park. This report documents the first stage of the process of preparing the Plan – that is, the preparation of a flood study report. The study area consists of a portion of the Lane Cove River floodplain and those City of Ryde areas which drain in a northeasterly or easterly direction to it. Much of the 1,558ha study area is developed. It is crossed by a number of major roads including Epping Road, Lane Cove Road and the M2 Motorway and the underground Epping to Chatswood railway line. The consultants drew on both previous flood study reports and additional community consultation to review historical records about flood problems that have been experienced in the catchment and this process found that the two most widely reported floods were in November 1984 and February 1990. Computer-based (DRAINS) hydrologic models and (TUFLOW) hydraulic models have been developed. While substantial efforts have been made to compile as best a picture as possible of several relatively recent floods (i.e. November 1984 and February 1990), the resultant rainfall and water level data sets were found to provide only very general information about the floods. As a consequence, while the models generally reproduce the observed flood regimes, formal calibration against those events was not possible. The modelling confirmed that the November 1984 event was worse than the February 1990 event and significant number of properties in natural depressions experienced overland flow inundation. Additionally, some properties located adjacent to open creek channels experienced substantial depths of water. Design flood event modelling followed and this report presents the results of modelling the 20 year average recurrence interval (ARI) flood, the 100 year ARI flood and the Probable Maximum flood (PMF). The detailed DRAINS and TUFLOW models provide a sound platform for the further flood modelling tasks that will be undertaken during preparation of the Floodplain Risk Management Study and Plan. SOFTWARE The DRAINS software (Reference 7) has principally been used to model the hydrologic regime of the study area. It is a comprehensive hydrologic modelling program for designing and analysing various types of catchments and urban stormwater drainage systems and includes hydraulic modelling capabilities for pipes and overland flowpaths. The software is widely used in Australia and Council itself has used DRAINS for many years. The DRAINS model version is 2009.06. While it follows that DRAINS software is suitable for undertaking both hydraulic and hydrologic assessments of urban catchments – and both capabilities have been used in this study – it is important to note that the pipe hydraulic analysis undertaken within the subsequent hydraulic modelling phase (refer Chapter 4) provides a more comprehensive picture of both pipe and overland flow rates. The widely used and Australian developed TUFLOW software (Reference 6) was chosen as the hydraulic modelling tool for use in the study because of its capability to simulate flood flows along both open watercourses and potentially complicated networks of overland flowpaths such as occurs in the study area. The technical description of the TUFLOW model and its specific application to the study area is provided in Appendix C. The TUFLOW build model is 2008-08-AF- ISP. The following sections of the report describe the establishment and operation of the TUFLOW model to simulate: the November 1984 and February 1990 events using DRAINS-derived flows. The simulated flood levels and extents for this event were then compared with the historical information; and the design 5 year, 20 year, 50 year, 100 year ARI and PMF events.