Flood Risk Overlay 2026

This flood risk awareness mapping has been prepared using the results of a citywide, fit for purpose flood risk assessment, using the most up-to-date rainfall information, new flood modelling software and industry best practice methodologies. The flood risk awareness mapping is a product to create flood risk awareness. The flood risk awareness map: is non-statutory and does not impose regulatory controls; is based upon the combined effect of flood hazards and their likelihood, for all flood events up to and including the extreme flood event (probable maximum flood); has been developed using latest flood models; includes parts of the City that have been mapped for the first time; indicates degrees of risk, using the risk-based approach, through the following applied flood risk categories : Very high risk - Unsafe for people and vehicles, and buildings are subject to structural failure in frequent floods. Flood events are both frequent and usually of the highest hazard High risk - Unsafe for people and vehicles, and buildings are subject to failure in frequent flood events. Flood events are both relatively frequent and usually of high hazard. Medium risk - Unsafe for people and vehicles, and buildings are subject structural failure in rare flood events. Flood events can either be rare with high hazard or relatively frequent with lower hazard. Low risk - Relatively lower hazards in frequent to infrequent flood events. High hazards can only occur in rare and very rare flood events, when it is unsafe for people and vehicles and buildings can be subject to structural failure. Maximum regional flood extent - Only floods in very rare to extreme flood events. Extent of the floodplain associated with very rare events and can include hazard of any type (low or high). Flood risk is calculated using likelihood (AEP) and hazards (flood depth and flood velocity). Those areas within categories ‘Low’ through ‘Very high’ have been determined taking into account the geographic extent of flood depth and flood velocity (i.e. flood hazard classification using the Australian Institute for Disaster Resilience (AIDR) method) across the city for the statistical rainfall events identified below, combined with the likelihood of those events occurring (e.g. rare, infrequent, frequent etc.). The areas identified as 'Maximum regional flood extent' indicate the outer extent of the floodplain. In simple terms, this risk mapping represents the city-wide product of flood hazard and likelihood using a Risk Management approach for a present-day scenario. The statistical design rainfall ‘events’ used in the flood modelling that underpinned the preparation of this risk map are: 20% AEP (generally known as 1 in 5 or frequent flood event) 5% AEP (generally known as 1 in 20 or infrequent flood event) 1% AEP (generally known as 1 in 100 or infrequent flood event) 0.5% AEP (generally known as 1 in 200 or rare flood event) 0.2% AEP (generally known as 1 in 500 or rare flood event) 0.05% AEP (generally known as 1 in 2000 or extremely rare flood event) Extreme flood event本洪水风险意识地图基于全市范围、适配场景的洪水风险评估结果编制而成，采用了最新降雨数据、新型洪水建模软件以及行业最佳实践方法。 该洪水风险意识地图是用于提升公众洪水风险认知的专项成果。 该洪水风险意识地图具备以下属性： 1. 不具备法定强制效力，亦不施加任何监管管控措施； 2. 基于所有洪水事件（含极端洪水事件，即可能最大洪水（Probable Maximum Flood））的洪水灾害及其发生概率的综合影响； 3. 采用最新洪水建模技术开发完成； 4. 覆盖全市范围内首次开展测绘的区域； 5. 采用基于风险的评估方法，通过以下划定的洪水风险等级体系明确风险程度： - 极高风险：人员与车辆均不得进入，频发洪水会导致建筑结构失效。此类洪水事件发生频繁，且通常属于最高危害等级。 - 高风险：人员与车辆均不得进入，频发洪水会导致建筑结构失效。此类洪水事件发生相对频繁，且通常属于高危害等级。 - 中风险：人员与车辆均不得进入，罕见洪水会导致建筑结构失效。此类洪水事件或为高危害但发生频率极低，或为相对频发但危害程度较低。 - 低风险：在频发至偶发的洪水事件中，危害程度相对较低。仅在极端罕见的洪水事件中才会出现高危害，此时人员与车辆不得进入，建筑亦可能发生结构失效。 - 最大区域洪水范围：仅对应极罕见至极端洪水事件。即与极罕见事件相关的洪水漫滩范围，可包含任意类型（低或高）的洪水灾害。 洪水风险通过发生概率（AEP，Annual Exceedance Probability）与灾害参数（洪水水深及洪水流速）计算得出。"低"至"极高"风险等级的区域，是结合以下指定统计降雨事件中全市范围的洪水水深与洪水流速的地理分布（即采用澳大利亚防灾协会（Australian Institute for Disaster Resilience，简称AIDR）方法开展的洪水灾害分类），以及这些事件的发生概率综合确定的。被划定为"最大区域洪水范围"的区域代表洪水漫滩的外围边界。 简言之，本次风险地图以现状场景为基准，采用风险管理方法，综合呈现了全市范围的洪水灾害与发生概率的叠加成果。 本次风险地图编制所依托的洪水建模中，所使用的统计设计降雨"事件"包括： - 20% AEP（通常称为1/5年一遇，即频发洪水事件） - 5% AEP（通常称为1/20年一遇，即偶发洪水事件） - 1% AEP（通常称为1/100年一遇，即偶发洪水事件） - 0.5% AEP（通常称为1/200年一遇，即罕见洪水事件） - 0.2% AEP（通常称为1/500年一遇，即罕见洪水事件） - 0.05% AEP（通常称为1/2000年一遇，即极端罕见洪水事件） - 极端洪水事件