Morphological and fish mesohabitat dynamics following an experimental flood under different sediment availability

IF 2.8 3区 地球科学 Q2 GEOGRAPHY, PHYSICAL Earth Surface Processes and Landforms Pub Date : 2024-11-13 DOI:10.1002/esp.6025
Tulio Soto Parra, Emilio Politti, Guido Zolezzi
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Abstract

Experimental floods have been increasingly used as a promising practice to rehabilitate river ecosystems downstream of dams; however, the morphological and habitat dynamics they determine under different sediment supply conditions still poses relevant research and management questions. This study investigates the morphological and fish mesohabitat dynamics following an experimental flood, in two river reaches subject to different sediment supply regimes. We chose the lower Spöl River (Switzerland) as a relevant case study, subject to an experimental flood program for several years. Downstream of the dam, a tributary supplies large amounts of sediment to the Spöl dividing the study area into two homogeneous reaches with different sediment availability but similar flow conditions during the experimental flood. We analyzed and quantified the changes in morphology and fish habitat suitability for the Brown Trout (Salmo trutta) at the mesoscale in these two reaches caused by the 2021 experimental flood, which lasted 11 h and had a peak magnitude corresponding to a 1-year return interval in the pre-dam flow regime. We found almost no correlation between changes in the channel morphology and in habitat suitability for this event. In the upstream reach, located immediately downstream of the dam, we observed a narrower channel with a regular longitudinal sequence featuring nearly immobile coarse rapids, interspersed with more dynamic, finer riffles. Here, reach-scale morphodynamics and the shifts of the mesohabitat mosaic and the suitable habitats were below 10%. Conversely, the downstream reach, characterised by a wider channel and much higher sediment supply of well-sorted, finer bed material, was dominated by alternate bar instability and migration at the reach scale, which caused a 45% shift in its pre-flood habitat mosaic. Nevertheless, in the same reach, the overall suitability of habitats remained relatively unchanged. We attributed these different dynamics to two main factors: (i) more prolonged bedload mobility conditions and (ii) the occurrence of bar migration in the downstream reach compared to the upstream one. This study (i) underscores the critical importance of considering sediment supply from downstream tributaries when designing and monitoring the effects of experimental floods, (ii) supports the use of morphodynamic models in the related planning and monitoring phases and (iii) shows the relevance of integrating morphodynamics and eco-hydraulic analysis to support the implementation of such flow restoration programs.

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不同泥沙含量下的洪水实验后形态和鱼类中间栖息地的动态变化
实验性洪水已被越来越多地用作恢复大坝下游河流生态系统的一种有前途的做法;然而,在不同的泥沙供应条件下,它们所决定的形态和栖息地动态仍然提出了相关的研究和管理问题。本研究调查了在不同泥沙供应机制下,两条河流在实验性洪水过后的形态和鱼类中间栖息地的动态变化。我们选择了斯珀尔河下游(瑞士)作为相关案例进行研究,该河段已实施了多年的试验性洪水计划。大坝下游的一条支流为斯珀尔河提供了大量泥沙,将研究区域划分为两个同质河段,这两个河段的泥沙供应情况不同,但在试验性洪水期间的水流条件相似。我们分析并量化了 2021 年实验性洪水在这两个河段的中尺度上对褐鳟(Salmo trutta)的形态和鱼类栖息地适宜性造成的变化,实验性洪水持续了 11 个小时,其峰值相当于坝前水流系统中 1 年的重现间隔。我们发现,这次洪水造成的河道形态变化与栖息地适宜性变化之间几乎没有关联。在紧靠大坝下游的上游河段,我们观察到一条较窄的河道,其纵向序列较为规则,以几乎不动的粗激流为特征,中间夹杂着更具活力的细涟漪。在这里,河段尺度的形态动力学以及中间栖息地镶嵌和适宜栖息地的转移率均低于 10%。相反,下游河段的特点是河道更宽,沉积物供应量更大,河床材料分选更细,在河段尺度上,交替出现的栅栏不稳定性和迁移是其主要特征,这导致其洪水前栖息地组合发生了 45% 的变化。然而,在同一河段,栖息地的总体适宜性相对保持不变。我们将这些不同的动态变化归因于两个主要因素:(i) 与上游相比,下游河段的河床移动条件更长;(ii) 下游河段出现了条石迁移。这项研究(i)强调了在设计和监测试验性洪水影响时考虑下游支流泥沙供应的重要性,(ii)支持在相关规划和监测阶段使用形态动力学模型,(iii)表明了将形态动力学和生态水力分析相结合以支持此类水流恢复计划实施的相关性。
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来源期刊
Earth Surface Processes and Landforms
Earth Surface Processes and Landforms 地学-地球科学综合
CiteScore
6.40
自引率
12.10%
发文量
215
审稿时长
4 months
期刊介绍: Earth Surface Processes and Landforms is an interdisciplinary international journal concerned with: the interactions between surface processes and landforms and landscapes; that lead to physical, chemical and biological changes; and which in turn create; current landscapes and the geological record of past landscapes. Its focus is core to both physical geographical and geological communities, and also the wider geosciences
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