Mediterranean river systems of Andalusia, southern Spain, and associated deltas: A source to sink approach

Abstract

The northern shores of the semi-isolated Mediterranean Sea with its low tidal range and a relatively voluminous fluvial supply of sediments constitute an ideal delta forming environment. In this paper, we examine the present-day and multi-decadal behaviour of 26 river systems from Andalusia, southern Spain, forming deltas in the Alboran Sea, the westernmost basin in the Mediterranean Sea. Eastern, Central and Western Andalusian watersheds have been defined based on geomorphological, climatological and hydrological characteristics. A comprehensive data set has been compiled, including satellite images, aerial photographs, a digital elevation model, thematic maps, time series of precipitation, temperature and water discharge, and the damming history of individual river basins. This data set has been used to analyse basin morphology and hydrology, and anthropogenic impact. Several modelling approaches have been applied to obtain the water budget and mean annual sediment yield of 12 of the 26 studied river systems. In addition, the periodicities of water discharge events and their possible link with North Atlantic Oscillation (NAO) fluctuations have been also studied. A decreasing trend has been observed in most water discharge time series during the last decades, which has been attributed to natural factors. Although it could have been expected that the diminution of water discharge may have caused a reduction in sediment load, calculated sediment discharge time series do not show any significant tendency. In general, sediment yield shows an opposite relationship with basin area. A comparative analysis of Spanish Mediterranean deltas indicates that in terms of sediment transport Andalusian river systems are quite efficient despite the small size of their catchments. Repetitive flood events and the consequent suspension plumes off river mouths play a major role in the development of deltaic and prodeltaic bodies. Nowadays, 42% of the study area is regulated, although to date the effect of dam building is hardly noticeable on river mouths.