Special issue: analysis and modelling of sediment transfer in Mediterranean river basins

Abstract

The characteristic conditions found in most Mediterranean and many other semiarid regions are those situations where current water use already equals and often exceeds water availability and where the hydro-meteorological regime shows a strong variability. In addition, water demand is commonly out-of-phase in relation to water resources, especially at the seasonal scale. If those areas rely on surface water resources to a large extent, they are particularly vulnerable to severe erosion (because of scarce vegetation cover of the soil and high rainfall intensity/energy), loss of fertile soils and subsequent sedimentation of reservoirs that are designed for water supply. As a consequence, this loss of reservoir retention volume may lead to a significant reduction of water availability within a period of a few years or decades. Therefore, erosion and sedimentation issues have to be taken into account when analysing and implementing long-term sustainable strategies to secure future water supply through water management and to sustain soil productivity through land-use management in upstream catchments. In this context, it is necessary to focus research and innovative management issues on “typical” scales in time and space. From a scientific perspective, the adequate spatial process scales range from the plot to field or river-reach scale. The model scale also ranges from plot scale but expands to the meso-scale of river basins up to several thousands of square kilometres. From a management perspective, the spatial scale of interest is the meso-scale (or intermediate to large catchments scale) because this is the scale most relevant for management of water and land resources. Furthermore, it is important to account for the relevant landscape components (and their driving processes), such as hillslopes (runoff and erosion processes on the soil surface), channel network (transfer from sources i.e. connectivity and sediment transport in river systems) and lakes or reservoirs (deposition of sediments). The scientifically sound assessment of generation, transfer and storage processes of water and sediment fluxes can be conducted in a dynamic and quantitative way by field monitoring, on the one hand, and the application and adaptation of adequate hydrological and sediment-transport models, on the other. Due to upstream–downstream relationships, connectivity factors that influence runoff generation, sediment production and water resources, as well as the effects of water management measures, usually affect the entire area of river basins and thus need to be included in this assessment. This special issue of the Journal of Soils and Sediments deals with the research questions identified above. It comprises 11 articles with different methodological backgrounds (monitoring/measurement techniques, methods of data analysis and process-oriented modelling); from different Mediterranean regions, in particular from the Iberian Peninsula, Europe, and from northeast Brazil; different spatial scales (from micro-catchments covering a few hectares up to the large catchments of the Lower Ebro and the Upper Jaguaribe, i.e. the scale of 10 km); and different time scales (from the event scale, i.e. a few hours, up to several decades). Most of the articles are based on selected presentations given at the 6th International Conference on Water Resources and Environment Research that was convened at Koblenz (Germany) from 3 to 7 June 2013. The focus of the conference was to foster an integrative understanding of water and the J. C. de Araujo (*) Department of Agricultural Engineering, Federal University of Ceara, Fortaleza, CE 60356-000, Brazil e-mail: jcaraujo@ufc.br