Abstract Explosive volcanic eruptions generate a range of physical processes with great hazard potential. Subsequent fluvial processes have major effects on channel and valley-floor geometry, potentially resulting in extreme sediment and large wood (LW) yields. The associated impacts can be severe, both immediately and in the longer term as river channels are permanently reworking the large volumes of their own sediment. The city of Chaiten (Lake District, Chile) is a unique case, since sediment- and wood-laden flows in the Blanco River may still pose, even 11 years after the paroxysmal eruption of the Chaiten volcano, large urban sectors at risk. Thoroughly assessing the flood hazard and the generated impact for such urban settings is, hence, of utmost importance. To achieve this goal, we designed a workflow integrating the following tasks: (i) hydrologic modelling at catchment scale employing the HEC-HMS model to obtain flood hydrographs for a 30 and 100 years flood, respectively, (ii) estimation of the sediment fluxes to establish reliable boundary conditions for (iii) the subsequent extensive 2D flood modelling with the model Iber in the unconfined floodplain and delta of the Blanco River including also the effects of possible clogging of the “Austral Road” bridge with transported LW, (iv) quantification of a series of building performance indicators for a set of 13 residential buildings as a basis for subsequent vulnerability and risk assessment. We found that, even without a new volcanic eruption as a potent hazard trigger, vast urban sectors are still exposed to flooding, in particular if LW gets entrapped at the “Austral Road” bridge and channel outbursts occur as a consequence of the reduced conveyance and backwater rise. Our results indicate a great spatial variability of flood impacts, being worst in the urban areas either located closely to the channel outburst locations or where overland flow locally channelizes on concave floodplain topographies. Based on our findings we outline provisional recommendations for risk mitigation and informed land use planning.

中文翻译：

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解开受火山爆发严重扰乱的河流洪水对建筑环境的影响

摘要 火山爆发会产生一系列具有巨大危害潜力的物理过程。随后的河流过程对河道和谷底几何形状有重大影响，可能导致极端沉积物和大量木材 (LW) 产量。相关的影响可能是严重的，无论是直接的还是长期的，因为河道正在永久性地改造其自身的大量沉积物。柴滕市（智利湖区）是一个独特的案例，因为布兰科河中充满沉积物和木材的水流可能仍然构成，即使在柴滕火山爆发性喷发 11 年后，大型城市部门仍处于危险之中。因此，彻底评估洪水灾害及其对此类城市环境的影响至关重要。为了实现这一目标，我们设计了一个集成以下任务的工作流：(i) 流域尺度的水文建模采用 HEC-HMS 模型分别获得 30 年和 100 年洪水的洪水过程线，(ii) 估计沉积物通量，为 (iii) 随后的广泛二维洪水建立可靠的边界条件在无限制的洪泛区和布兰科河三角洲中使用模型 Iber 进行建模，包括运输 LW 可能堵塞“Austral Road”桥梁的影响，(iv) 对一组 13 个住宅的一系列建筑性能指标进行量化建筑物作为后续脆弱性和风险评估的基础。我们发现，即使没有新的火山爆发作为潜在的危险触发因素，广大的城市地区仍然面临洪灾，特别是如果 LW 被困在“Austral Road”桥上，并且由于输送量减少和回水上升而导致渠道突爆。我们的结果表明洪水影响的空间变化很大，在靠近河道爆发位置或地表水流在凹形洪泛平原地形上局部形成河道的城市地区最为严重。根据我们的调查结果，我们概述了风险缓解和知情土地利用规划的临时建议。