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Vegetation encroachment ratios in regulated and non-regulated Mediterranean rivers (Spain): An exploratory overview
Journal of Hydro-environment Research ( IF 2.4 ) Pub Date : 2019-12-07 , DOI: 10.1016/j.jher.2019.11.006
Diego García de Jalón , Vanesa Martínez-Fernández , Khosro Fazelpoor , Marta González del Tánago

Vegetation encroachment is an expected response of rivers to a decrease in their flow variability and flood magnitude and frequency. It frequently occurs together with channel narrowing and a decrease in braiding, both of which are likely associated with different human alterations but most frequently with river damming. Vegetation encroachment ratios display a wide range of values according to local hydrologic and geomorphic contexts and dam operation management, and thus, they are very site specific. As vegetation interacts with fluvial processes, understanding the mechanisms that promote encroachment is important for predicting river trends and designing proper management and restoration measures. Our research aimed to explore the causal relationship between flow regulation and vegetation encroachment in Mediterranean rivers in Spain. We quantified vegetation encroachment and channel changes over the last 50 years in 13 river reaches, 5 of which corresponded to non-regulated rivers and 8 of which were located in rivers regulated by large dams. We analysed aerial orthophotographs from 1956, 1977 and 2011 or later up to 2014, according to image availability. We considered 1956 conditions as a reference and quantified ratios of changes in riparian vegetation cover, active channel width and braiding index over two periods, 1956–1977 and 1978–2011. We quantified the changes in the flow regime and clustered rivers according to their hydrological pattern, looking for potential hydrological drivers of the observed changes over time.

Vegetation encroachment, channel narrowing and braiding decreases occurred in all the studied rivers. Significant differences in annual ratios between the studied periods were found for both vegetation encroachment and channel narrowing, but no statistically significant differences were found between the regulated and non-regulated rivers or between the hydrological river groups previously clustered by flow variables. After discussing existing literature, we suggest a multi-scale approach to understanding river changes over time, encompassing larger historical perspectives. We hypothesize a generalized hydrologic decline since the beginning of the 20th century affecting rivers at the broad-regional scale would be overlapping the effects of land cover changes (i.e., renaturalization) at the catchment scale in reducing flood intensity and sediment supply. River damming would reinforce these patterns at river segment scale, in turn overlapping the influence of local geomorphic and ecological features. This hypothesis, which should be tested by further research, may explain the constancy of encroachment and channel narrowing regionally reported but with a wide variety of change ratios, determining converging trajectories of Iberian rivers that have also been found in other regions.



中文翻译:

受管制和不受管制的地中海河流中的植被入侵率(西班牙):探索性概述

植被侵蚀是河流对流量变化性和洪水幅度及频率降低的预期反应。它经常与河道变窄和编织减少一起发生,这两种情况都可能与不同的人类改造有关,但最常见的是与河坝筑坝有关。根据当地的水文和地貌环境以及大坝的运营管理,植被入侵率显示出广泛的数值,因此,它们是非常特定于地点的。由于植被与河流过程相互作用,因此,了解促进侵蚀的机制对于预测河流趋势以及设计适当的管理和恢复措施非常重要。我们的研究旨在探讨西班牙地中海河流中流量调节与植被侵蚀之间的因果关系。我们对过去50年中13个河段的植被侵蚀和河道变化进行了量化,其中5个对应于非管制河流,其中8个位于由大坝控制的河流中。根据图像的可用性,我们分析了1956年,1977年和2011年或更晚至2014年的航空正射照片。我们将1956年的条件作为参考,并量化了1956-1977年和1978-2011年两个时期的河岸植被覆盖度,活动河道宽度和编织指数的变化率。我们根据河流的水文模式量化了流态和聚集河流的变化,寻找随时间变化的潜在水文驱动因素。其中5条对应于非管制河流,其中8条位于由大坝管制的河流中。根据图像的可用性,我们分析了1956年,1977年和2011年或更晚至2014年的航空正射照片。我们将1956年的条件作为参考,并量化了1956-1977年和1978-2011年两个时期的河岸植被覆盖度,活动河道宽度和编织指数的变化率。我们根据河流的水文模式量化了流态和聚集河流的变化,寻找随时间变化的潜在水文驱动因素。其中5条对应于非管制河流,其中8条位于由大坝管制的河流中。根据图像的可用性,我们分析了1956年,1977年和2011年或更晚至2014年的航空正射照片。我们将1956年的条件作为参考,并量化了1956-1977年和1978-2011年两个时期的河岸植被覆盖度,活动河道宽度和编织指数的变化率。我们根据河流的水文模式量化了流态和聚集河流的变化,寻找随时间变化的潜在水文驱动因素。我们将1956年的条件作为参考,并量化了1956-1977年和1978-2011年两个时期的河岸植被覆盖度,活动河道宽度和编织指数的变化率。我们根据河流的水文模式量化了流态和聚集河流的变化,寻找随时间变化的潜在水文驱动因素。我们将1956年的条件作为参考,并量化了1956-1977年和1978-2011年两个时期的河岸植被覆盖度,活动河道宽度和编织指数的变化率。我们根据河流的水文模式量化了流态和聚集河流的变化,寻找随时间变化的潜在水文驱动因素。

所有研究的河流都发生了植被侵蚀,河道变窄和编织减少的现象。研究期之间在植被侵蚀和河道变窄方面的年比率存在显着差异,但在调节河与非调节河之间或先前由流量变量聚类的水文河群之间,没有发现统计学上的显着差异。在讨论了现有文献之后,我们建议采用一种多尺度的方法来理解随着时间的推移而发生的河流变化,包括更大的历史观点。我们假设,自20世纪初以来,在广泛区域范围内影响河流的水文状况将普遍下降,这将与土地覆盖变化的影响重叠(例如,减少流域的洪灾强度和减少沉积物供应)。河流筑坝将在河段规模上加强这些模式,从而重叠局部地貌和生态特征的影响。该假设有待进一步研究验证,可以解释区域报告的侵蚀和河道狭窄的恒定性,但变化率变化很大,从而确定了在其他地区也发现的伊比利亚河流的汇合轨迹。

更新日期:2019-12-07
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