Forested catchments are critical to water supply in major cities. Many of these catchments face the threat of postwildfire erosion, which can contaminate reservoir water. The aim of this paper is to determine the probability and duration of disruptions to treatability due to runoff‐generated debris flows in the first year after a wildfire, before substantial vegetation recovery takes place. We combine models of reservoir hydrodynamics, postfire erosion, and stochastic rainfall to determine probability and magnitude of sediment concentration at the reservoir water offtake. Central to the paper is our technique for linking model components into a risk framework that gives probabilities to the number of days that the turbidity threshold for treatment is exceeded. The model is applied to the Upper Yarra reservoir, which is the linchpin of the water supply system for Melbourne in SE Australia. However, the framework is applicable to other unfiltered water supply systems where suspended sediment is a risk to treatability. Results show that postwildfire erosion poses a substantial threat, with a relatively high probability (annual exceedance probability = 0.1–0.3) of water being untreatable for >1 year following a high‐severity wildfire. Important factors that influence the risk include postwildfire runoff potential, reservoir temperature, and the amount of clay‐sized grains in eroding headwaters. Assumptions about spatial‐temporal rainfall attributes, reservoir hydrodynamics, and the catchment erosion potential are all important sources of error in our estimate of risk. Our approach to risk quantification will help support planning, risk management, and strategic investment to mitigate impacts.

中文翻译：

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未过滤供水系统中水可处理性的后火侵蚀可能性和后果

森林集水区对大城市的供水至关重要。这些集水区中的许多面临着野火侵蚀的威胁，可能污染水库的水。本文的目的是确定在野火发生后的第一年，径流产生的泥石流破坏可治愈性的可能性和持续时间，然后才恢复大量植被。我们结合水库流体动力学，火灾后侵蚀和随机降雨的模型来确定水库取水口中泥沙浓度的概率和大小。本文的核心是我们将模型组件链接到风险框架的技术，该技术可提供超过处理浊度阈值的天数的可能性。该模型已应用于上亚拉河水库，这是澳大利亚东南部墨尔本的供水系统的关键。但是，该框架适用于其他未过滤的供水系统，在这些系统中悬浮的沉积物会影响可处理性。结果表明，野火后的侵蚀构成了重大威胁，在高烈度的野火之后，> 1年的水不可治愈的可能性相对较高（年超标概率= 0.1–0.3）。影响该风险的重要因素包括野火后的径流潜力，储层温度以及源头不断侵蚀的粘土颗粒的数量。关于时空降雨属性，水库水动力和流域侵蚀潜力的假设都是我们评估风险的重要误差来源。我们的风险量化方法将有助于支持规划，风险管理，