Coastal hydrography from Douro River mouth to Cape Finisterre

Abstract

A proper understanding of a shelf process is a prerequisite of an operational system of coastal observations and forecast. The hydrology in the northern part of the western Iberian shelf is far from being fully understood. This is particularly true for winter, when extreme events occur. Landward winds combined with high river runoff cause pile-up of water at the coast and tend to induce coastal currents. Rivers Douro and Minho are the major supplies of freshwater to the sea off the northern west coast of the Iberian Peninsula. Their runoff is concentrated in winter, statistically peaking in February-March. The goal of this work is to characterize the hydrology of the area of potential development of a Northwest Iberian Coastal Current. Hydrographic (CTD) surveys were designed to cover the whole shelf area from the Douro River mouth to Cape Finisterre, in different runoff and wind forcing conditions during winter 2006 and 2007. Freshwater outflow at the Crestuma-Lever dam was taken as representative of the total Douro river runoff. The observations took place when river flow was 250-600 m3/s, and frontal systems crossed the area. Although the presence of estuarine induced buoyancy was evident in the hydrographic structures, their modifications responded mainly to the wind. Absence of wind was required for the estuarine signal to be noticed on the shelf at low runoff, when it was most noticeable in the salinity and turbidity