Flood risk awareness map January 2025

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集基于全域适配需求的城市洪水风险评估成果编制而成，采用最新降雨数据、新型洪水模拟软件及行业最佳实践方法。本洪水风险意识地图属于洪水风险科普宣传产品，具备以下特征：不具备法定效力，亦不施加监管管控；基于所有直至极端洪水事件（可能最大洪水（Probable Maximum Flood））在内的各类洪水灾害及其发生可能性的综合影响；采用最新洪水模型开发完成；涵盖全市首次完成测绘的区域；通过风险分级方法，结合以下应用洪水风险类别标注风险等级：
1. "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率高且通常具备最高灾害等级。
2. "高风险"：人员与车辆均不得进入，频发洪水事件会导致建筑结构失效。此类洪水事件发生频率相对较高且通常具备较高灾害等级。
3. "中风险"：人员与车辆均不得进入，罕见洪水事件会导致建筑结构失效。此类洪水事件要么为高灾害等级的罕见事件，要么为灾害等级较低的相对频发事件。
4. "低风险"：偶发至频发洪水事件的灾害等级相对较低，仅在极罕见洪水事件中才会出现高灾害等级，此时人员与车辆不得进入，且建筑可能发生结构失效。
"最大区域洪水范围"：仅指极罕见至极端洪水事件的情形，对应极罕见事件相关的河漫滩范围，可涵盖任意类型（低或高）的灾害。
洪水风险通过发生可能性（年度超越概率（Annual Exceedance Probability, AEP））与灾害（洪水水深及洪水流速）综合计算得出。被划分为"低"至"极高"风险等级的区域，是结合全市范围内以下列明的统计降雨事件对应的洪水水深与洪水流速的地理分布（即采用澳大利亚灾害恢复协会（Australian Institute for Disaster Resilience, AIDR）方法开展的洪水灾害分级），并结合各类事件的发生概率（如罕见、偶发、频发等）综合确定的。被标识为"最大区域洪水范围"的区域代表河漫滩的外围边界。简言之，本风险地图以风险管理方法针对当前情景，综合体现了全市范围的洪水灾害与发生可能性的对应关系。
支撑本风险地图编制的洪水模拟所采用的统计设计降雨"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