Impact of channel bar form and grain size variability on estimated stranding risk of juvenile brown trout during hydropeaking
Impact of channel bar form and grain size variability on estimated stranding risk of juvenile brown trout during hydropeaking
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DOI：
10.1002/esp.3552
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发表时间：
2014-09-30
影响因子：
3.3
通讯作者：
Habersack, Helmut
中科院分区：
文献类型：
--
作者：
Hauer, Christoph;Unfer, Guenther;Habersack, Helmut
水力峰化导致流量和相应水位的人为波动，沿着砾石坝和河岸的基流和峰流之间有明显的降水区域。在本研究中，调查了奥地利的16个水峰河段，以评估根据不同的砾石坝类型和微地形粗糙度的差异，估计一年中褐鲑鱼幼鱼搁浅风险的可能差异。在水动力-数值模拟的基础上，在研究设计中实施了一种预测性生境模拟方法。结合不同航道坝的粒度采样，建立了概念性搁浅风险模型。结果表明，在流量比为1：3、1：5和1：10的情况下，试验点的估计搁浅风险存在很大的变异性。关于建立流量坡度的法定阈值的讨论，例如，流量比基流量/峰值流量为1：5(冬季基流条件)时，与夏季基流条件下1：2的比例相比，脱水区域的空间范围和相关的估计搁浅风险的差异很小。通过采样和粒度分布分析，解决了微观表面粗糙度问题。粒度分布的统计测试表明，所调查的砾石棒的表面材料成分之间存在显著差异。这些差异是明显的，特别是对于较粗的部分(d(90))，这是重要的，作为一年中幼年褐鲑鱼的掩护。颗粒大小在栖息地用途和水力学方面的这些方面已在概念SRM中得到解决。结果表明，与例如交替的砾石棒相比，点棒形态对搁浅风险的敏感度尤其低。考虑到高山河流的多重压力，讨论了沙坝形成和相关的自形成过程对结构特征的改善，作为未来缓解措施的可能选择，以减少水峰的负面影响。版权所有(C)2014 John Wiley&Sons，Ltd.
Hydropeaking leads to artificial fluctuations in discharge and corresponding water levels with pronounced dewatering areas between base and peak flow along gravel bars and channel banks. In the present study, 16 hydropeaking reaches in Austria were investigated to assess possible differences in the estimated stranding risk for young of the year brown trout according to different gravel bar types and differences in microtopography roughness. Based on hydrodynamic-numerical modelling, a predictive habitat modelling approach was implemented in the study design. Accompanied by grain size sampling along the various channel bars, a conceptual stranding risk model (SRM) was developed. The results showed that a high variability in estimated stranding risk exists for the tested sites considering discharge ratios of 1:3, 1:5 and 1:10. With respect to the discussion of establishing legal thresholds for ramping ratios in discharge, it was documented that, exemplarily, a discharge ratio base flow/peak flow of 1:5 (winter base flow conditions) could cause minor differences in the spatial extent of dewatering areas and the related estimated stranding risk for juvenile brown trout compared to a ratio of 1:2 for summer base flow conditions. Microtopographic roughness was addressed due to sampling and analysis of grain size distributions. Statistical testing of grain size distributions revealed significant differences between the surface material compositions of the investigated gravel bars. Those differences are evident, particularly for the coarser fraction (d(90)), which is important as cover for young of the year brown trout. These aspects of grain size in habitat use and hydraulics have been addressed in the conceptual SRM. The results showed that point bar morphology, in particular, was less sensitive to the risk of stranding compared to, for example, alternating gravel bars. Considering the multiple pressures for alpine rivers, the improvement of structural features due to bar formation and related self-forming processes is discussed as a possible alternative for future mitigation measures to reduce the negative impacts of hydropeaking. Copyright (c) 2014 John Wiley & Sons, Ltd.