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首页> 外文期刊>Estuarine Coastal and Shelf Science >Sedimentary characterization of bed types along the Guadiana estuary (SW Europe) before the construction of the Alqueva dam
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Sedimentary characterization of bed types along the Guadiana estuary (SW Europe) before the construction of the Alqueva dam

机译：在Alqueva大坝建造之前，沿瓜迪亚纳河口（欧洲西南部）沉积物的沉积特征

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摘要

The Guadiana River estuary is one of the most important mesotidal fluvio-marine systems of the south-western Iberian Peninsula. The river mouth was formed as a narrow channel that was excavated by fluvial incision during the Pleistocene lowstand and was then flooded 6500 years ago. The estuary is in an advanced state of sediment infilling in its proximal part, due to its narrow morphology, which prevents passage of sediment through to the open coast. Consequently, sediment is accumulating in the river mouth, which causes progradation. The analysis of the sediments into the estuarine channel (grain size, organic carbon content) and bedform distribution (Side-Scan Sonar) allows a distinction between two types of sedimentation to be made: a fluvial—marine sedimentation (favoured by tidal action) and an autochthonous sedimentation that is related to water mixing. The net transport of sediments is towards the sea because of the tidal current asymmetry. The autochthonous deposits and the sediments from the extreme fluvial floods that tides are unable to rework are preserved on the meandering convex margins under low tidal velocities. These areas acquire a lateral tidal-bar morphology with cohesive beds because the narrow geometry of the estuary inhibits the presence of longitudinal tidal bars, as may be expected in tide-dominated systems. The higher energy zones (deeper zones of the channel) become bypassing channels where the flocculated material cannot be settled on the bottom; this part of the channel then develops sandy beds with mesoforms as ebb-oriented two-dimensional and three-dimensional dunes (sand waves and megaripples).
机译：瓜迪亚纳河河口是西南伊比利亚半岛最重要的中游河流-海洋系统之一。河口形成为一条狭窄的河道，在更新世低水位期通过河流切口开挖，然后在6500年前被洪水淹没。由于其狭窄的形态，河口处于近端充满沉积物的高级状态，这阻止了沉积物穿过海岸。因此，沉积物在河口中积聚，从而导致沉积。对进入河口通道的沉积物（粒度，有机碳含量）和床形分布（Side-Scan Sonar）的分析可以区分两种沉积：河床-海洋沉积（受潮气作用）和与水混合有关的土生土沉。由于潮流的不对称性，沉积物的净输送是向着海洋。在潮汐速度低的情况下，潮汐无法修复的极端河流洪水造成的水生沉积物和沉积物被保留在蜿蜒的凸缘上。这些区域获得了具有凝聚层的横向潮汐带形态，因为河口的狭窄几何形状抑制了纵向潮汐带的存在，这在以潮汐为主的系统中是可以预期的。较高能量的区域（通道的较深区域）成为旁路通道，在这些通道中，絮凝的物料无法沉降在底部。然后，河道的这一部分会形成具有中等形状的沙床，如退潮的二维和三维沙丘（沙波和巨型波纹）。

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