Abstract
The Guadiana estuary is a coastal system located in the southwest of the Iberian Peninsula and is the natural border between Portugal and Spain. It is a rock-bounded estuary which extends along more than 40 km and is characterized by a semidiurnal mesotidal regime. This paper represents an approach to the bedload transport across two flow sections located in the fluvial and marine domains. In the fluvial profile, the most frequent bedform is the plane bed. In the marine area the bed of the deep channel is composed of well-sorted sand, while a lateral bar displays partially cohesive sediments with dominant fine sands in a matrix of clayey silts. Data were acquired during spring and neap tides. Near-bottom water velocities were registered by an acoustic Doppler current profiler (ADCP). Density and bed rugosity were determined in sediment samples. These data were employed using Bagnold’s equation (1963) to quantify the potential bedload (Qb). Further, real bedload values (Sb) were obtained by using Poliakoff traps. The comparison of the results of Qb under both ebb and flood conditions demonstrated a clear river-to-sea net transport in both sectors. The values of Sb were lower than those of Qb in every condition. The sand input across the fluvial estuary cannot supply the potential bedload in the lower domain of the channel, thereby causing a deficit that explains this lack of agreement between potential and real transport.
Highlights
The calculation of the potential bedload transported by fluvial and tidal currents has been a focus of attention over the last few years because understanding the arrival of sand from the continent to the coast has become an important aspect of the correct management of coastal systems [1,2,3,4,5,6,7,8,9,10]
The sand input across the fluvial estuary cannot supply the potential bedload in the lower domain of the channel, thereby causing a deficit that explains this lack of agreement between potential and real transport
This paper has demonstrated the utility of this kind of comparison, since, in some conditions, a disparity exists between potential and real transport
Summary
The calculation of the potential bedload transported by fluvial and tidal currents has been a focus of attention over the last few years because understanding the arrival of sand from the continent to the coast has become an important aspect of the correct management of coastal systems [1,2,3,4,5,6,7,8,9,10]. The sedimentary material transported along the water-bed interface can be understood as a bedload. This material is transported by rolling, dragging, or saltation, with regard to the individual movement of the particles, this movement can be regarded in a collective way with reference to the migration of bedforms. Most works elaborated during the last decades of the twentieth century agree that bedforms (dimensions and orientation) are a good parameter with which to qualitatively estimate bedload [10,11,12] and are especially useful in multidirectional systems such as estuarine channels [8,13]
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