Abstract Freshwater pearl mussels have high ecological demands on their habitat. For natural reproduction and distribution, they need a colmation-free porespace in the substrate and sufficient host fish for their parasitic stage of life. In Austria, river alterations and anthropogenic activities in the catchments are causing habitat degradation for both, the freshwater pearl mussel Margaritifera margaritifera and its host fish Salmo trutta. Due to the lack of reference stretches, sediment transport and sediment deposition in the main channel cannot be measured directly. In (semi-) natural river sections as well as in sections with anthropogenically caused over-width of the river bed, however, it can be observed that the river itself forms a two-stage ditch within a few years. This study examines the deposits of those rivers and describes hydraulic and sedimentological processes influencing the geometry within the main channel below bankfull stage. A possible correlation between the mean annual discharge and the instream geometry could be determined. A simple formula is given as a recommendation for action, which can be used for pre-dimensioning of channel geometry below the bankfull stage in case of river restoration of freshwater pearl mussel habitats. This equation also allows authorities to review planning services for ecologically negative interventions and to recommend a method of implementing measures below bankfull stage.

中文翻译：

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双峰粒度河流形态条件研究：淡水珍珠贻贝栖息地的挑战和新见解

摘要 淡水珍珠贻贝对其栖息地的生态要求很高。为了自然繁殖和分布，它们需要在基质中有一个无孔洞空间，并且需要足够的寄主鱼来适应它们的寄生生活阶段。在奥地利，流域的河流改建和人为活动导致淡水珍珠贻贝 Margaritifera margaritifera 及其寄主鱼 Salmo trutta 的栖息地退化。由于缺乏参考河段，无法直接测量主河道中的泥沙输移和泥沙沉积。然而，在（半）天然河段以及人为造成河床过宽的河段中，可以观察到河流本身在几年内形成了两级沟渠。这项研究检查了这些河流的沉积物，并描述了水力和沉积学过程，影响了满岸阶段以下主河道内的几何形状。可以确定年平均流量和河道几何形状之间可能的相关性。给出了一个简单的公式作为行动建议，在淡水珍珠贻贝栖息地的河流恢复的情况下，该公式可用于在满岸阶段以下的河道几何形状的预先确定尺寸。这个等式还允许当局审查生态负面干预的规划服务，并推荐一种在银行充分阶段以下实施措施的方法。可以确定年平均流量和河道几何形状之间可能的相关性。给出了一个简单的公式作为行动建议，在淡水珍珠贻贝栖息地的河流恢复的情况下，该公式可用于在满岸阶段以下的渠道几何形状的预先确定尺寸。这个等式还允许当局审查生态负面干预的规划服务，并推荐一种在银行充分阶段以下实施措施的方法。可以确定年平均流量和河道几何形状之间可能的相关性。给出了一个简单的公式作为行动建议，在淡水珍珠贻贝栖息地的河流恢复的情况下，该公式可用于在满岸阶段以下的河道几何形状的预先确定尺寸。这个等式还允许当局审查生态负面干预的规划服务，并推荐一种在银行充分阶段以下实施措施的方法。