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Multidecadal Evolution of the Turbidity Maximum Zone in a Macrotidal River Under Climate and Anthropogenic Pressures
Journal of Geophysical Research: Oceans ( IF 3.6 ) Pub Date : 2021-04-19 , DOI: 10.1029/2020jc016273
I. Jalón‐Rojas 1, 2 , Y. M. Dijkstra 3 , H. M. Schuttelaars 3 , R. L. Brouwer 3, 4 , S. Schmidt 1 , A. Sottolichio 1
Affiliation  

Climate and human pressures can influence the evolution of estuarine sediment dynamics concurrently, but the understanding and quantification of their cause–effect relationships are still challenging due to the occurrence of complex hydro‐morpho‐sedimentary feedbacks. The Garonne Tidal River (GTR, upper Gironde Estuary, France) is a clear example of a system stressed by both anthropogenic and climate change, as it has been subject to decreasing river discharges, natural morphological changes, and gravel extraction. To understand the relative effect of each hydrological and geomorphological pressure on the turbidity maximum zone (TMZ), the sediment dynamics in the GTR over the last six decades was evaluated using the width‐averaged idealized iFlow model. Model results show a gradual increase in tidal amplitude and currents over the decades that has led to the upstream shift of the landward sediment‐transport capacity components (external M4 tide, spatial settling lag, and tidal return flow). The upstream displacement of the TMZ between the 1950s and the 2010s was estimated to be at least 19 km, of which about three fourth was induced by geomorphological changes and one fourth by hydrological changes. Concerning the geomorphological changes, the natural evolution of the lower Gironde morphology was the main pressure inducing the displacement of the TMZ in the GTR. Anthropogenic and natural changes in morphology and bed roughness in the GTR itself also contributed to this evolution. The natural geomorphological changes were, in turn, probably promoted by the evolution of sediment dynamics, so this study reveals the closed circle that governs the intensification of the TMZ.

中文翻译:

气候和人为压力下巨潮河道浊度最大区的年代际变化

气候和人为压力可以同时影响河口沉积物动力学的演变,但是由于复杂的水-形态-沉积反馈的发生,对它们的因果关系的理解和量化仍然具有挑战性。加龙河(Garonne)潮汐河(GTR,法国吉伦特河口上游)是人类活动和气候变化双重压力的明显例子,因为河流流量减少,自然形态变化和砾石提取受到影响。为了了解每个水文和地貌压力对最大浊度区(TMZ)的相对影响,使用宽度平均的理想化iFlow模型评估了过去60年中GTR中的沉积物动力学。4潮,空间沉降滞后和潮汐回流)。在1950年代至2010年代之间,TMZ的上游位移估计至少为19 km,其中约四分之三是由地貌变化引起的,四分之一是由水文变化引起的。关于地貌变化,吉伦特河下部形态的自然演化是引起TMZ在GTR中位移的主要压力。GTR本身在形态和床粗糙度方面的人为和自然变化也促成了这一演变。反过来,自然地貌的变化可能是由沉积动力学的演变所推动的,因此,本研究揭示了控制TMZ增强的闭合圆。
更新日期:2021-04-30
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