| Abstrakt: |
Recent flooding from three consecutive La Niña episodes has brought increased focus to dam flood operations across much of Australia, particularly within the eastern states (ABC News, 2022; The Guardian, 2022). For gated dams, it is typical for flood operations to be focused on balancing competing objectives relating to dam safety, water supply security, flood mitigation and environmental protection. Downstream impacts are usually the focus of flood mitigation, while lake level constraints are typically informed by dam safety and dam operability considerations. However, upstream inundation from elevated reservoir levels can be equally important during flood operations and is particularly relevant for reservoirs which have private and/or public assets upstream. To address the reliance on experiential and anecdotal evidence for flood operating rules, this study adopts a novel approach to quantitively assess upstream impacts of reservoir operation during floods, using Narracan Dam as a case study. The methodology encompasses configuring spillway gate operation in a 2D hydraulic model and testing a range of operator defined scenarios. Of the operating scenarios tested, it was found that storage operating level has negligible impact on depth, length and duration of flooding over Becks Bridge road upstream. A minor influence on flood hazard (depth × velocity) is observed, but adopting a more intensive operating approach (with more frequent gate changes) results in a minor reduction in DV but no change to the hazard rating. This study concludes that the existing storage operating approach at Narracan Dam, primarily informed by operational experience from past events, is effective at mitigating upstream flood impacts. Notwithstanding this, this study contributes to the development and refinement of evidencebased flood operating rules by evaluating the physical upstream impacts of reservoir operations. The adopted modelling and assessment framework can be applied to other dams with similar operational constraints and lead to enhanced community safety and overall flood resilience outcomes. [ABSTRACT FROM AUTHOR] |
