Flood_Risk_Overlay_2024_update01

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依托全域适配型城市洪水风险评估成果编制而成，采用了最新降雨数据集、新型洪水建模软件及行业通用最佳实践方法。本洪水风险意识地图系用于提升公众洪水风险认知的专项产品，其具备以下特征：不具备法定效力，亦不施加任何监管管控要求；基于包括极端洪水事件（可能最大洪水，probable maximum flood）在内的所有洪水场景下，洪水灾害与其发生概率的综合影响构建；采用最新洪水模型开发完成；覆盖本市范围内首次完成测绘的区域；采用基于风险的分级方法，通过以下洪水风险等级划分体系展示风险程度： 1. 极高风险区：人员与车辆通行均不安全，频繁洪水事件下建筑将发生结构性破坏，此类洪水事件发生频率较高且通常危害等级最高； 2. 高风险区：人员与车辆通行均不安全，频繁洪水事件下建筑将发生结构性破坏，此类洪水事件发生频率相对较高且通常危害等级较高； 3. 中风险区：人员与车辆通行均不安全，罕见洪水事件下建筑将发生结构性破坏，此类洪水事件要么发生概率极低但危害较高，要么发生频率相对较高但危害较低； 4. 低风险区：在频繁至偶发洪水事件中危害相对较低，仅在极罕见洪水事件中才会出现高危害场景，此时人员与车辆通行不安全，建筑亦可能发生结构性破坏； 5. 最大区域洪水范围：仅对应极罕见至极端洪水事件，为极罕见洪水事件相关的洪水漫滩（floodplain）范围，可涵盖任意类型（低或高）的洪水灾害。 洪水风险通过发生概率（年度超越概率，Annual Exceedance Probability，简称AEP）与灾害特征（洪水水深及洪水流速）综合计算得出。"低"至"极高"等级的区域，系通过将下述统计降雨事件下，全市范围内采用澳大利亚抗灾协会（Australian Institute for Disaster Resilience, AIDR）方法得到的洪水水深与流速地理分布（即基于该方法的洪水灾害分级），结合对应事件的发生概率（如罕见、偶发、频繁等）综合确定。 被划定为"最大区域洪水范围"的区域，代表全市洪水漫滩的外围边界。简言之，本风险地图采用风险管理方法，基于当前情景下的全域洪水灾害与发生概率综合成果编制而成。 支撑本次风险地图编制的洪水建模所采用的统计设计降雨"事件"包括： 20% AEP（通常称为1/5年一遇洪水，属频繁洪水事件）、 5% AEP（通常称为1/20年一遇洪水，属偶发洪水事件）、 1% AEP（通常称为1/100年一遇洪水，属偶发洪水事件）、 0.5% AEP（通常称为1/200年一遇洪水，属罕见洪水事件）、 0.2% AEP（通常称为1/500年一遇洪水，属罕见洪水事件）、 0.05% AEP（通常称为1/2000年一遇洪水，属极罕见洪水事件）、 极端洪水事件。