Sediment dynamics on the inner continental shelf of the Basque Country (N.Spain).

Uriarte, Adolfo (1998) Sediment dynamics on the inner continental shelf of the Basque Country (N.Spain). University of Southampton, Doctoral Thesis.

Abstract

Sediment dynamics over the continental shelf in the southeastern Bay of Biscay is investigated. Therefore, extensive fieldwork comprising measurements of river suspended sediment discharges and sediment retrieval, offshore of the major river months of the region is carried out. A more detailed study of the River Oria and adjacent continental shelf is undertaken, sampling for sea bed sediments, waves and currents, and changes in bathymetry (i.e. sediment volumes).

An algorithm is produced relating: drainage area extension, the maximum basin height and the vegetation cover, which uses a stepwise multiple regression analysis procedure. The equation derived for the prediction of annual suspended sediment loads for the region shows only minor differences (±5%) between the predictions and measurements. The formulae obtained are used to infer the total loads contributed by the remainder of the major rivers draining the investigated region. This allows to derive a total suspended sediment load value for all the northeastern Spanish region, which accounts for 1.57 million tonnes per year.

The kaolinite content and heavy metal concentrations (referred to their background levels) in sediment samples are used to infer transport paths at a general and detailed scale, respectively.

Wind and wave action are together responsible for a large part of the observed current patterns over the area. It has been found, that currents in the area are generated by the synergy of all forcing factors (waves, wind, river flow and tides), together with some undetermined inertia currents.

The nearshore-inner shelf boundary (i.e. closing depth) calculated for the area approximates the 25m isobath. This closing depth agrees very well with nearshore-inner shelf boundaries defined elsewhere, for exposed world-wide coastlines; and compares to closing depths of around 10m water depth, calculated for Spanish Mediterranean coastlines.

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