EROSION, FLOODING AND CHANNEL MANAGEMENT IN MEDITERRANEAN ENVIRONMENTS OF SOUTHERN EUROPE

Soil erosion by water is one of the most important land degradation pr ocesses in Mediterranean environments. This process is strongly linked to problems of flooding and channel management. This article reviews existing knowledge on these topics and defines research gaps. In the f ramework of environmental change studies it is important to consider s oil erosion at various spatial and temporal scales. Most field measure ments and modelling efforts have hitherto concentrated on water erosio n processes operating at the runoff plot scale. Soil erosion processes operating at other spatial scales have received much less attention i n the literature. Yet, there are indications that gully and channel er osion are probably the dominant sediment sources in a variety of Medit erranean environments. Beside water erosion, other erosion processes o perating within catchments, such as tillage erosion, land reshaping fo r land preparation (e.g., terracing) or soil quarrying can have signif icant impacts on soil profile truncation. Land use changes strongly af fect the intensity of these processes. The conditions, position and co nnectivity of the runoff and sediment generating areas within catchmen ts have a profound effect on flood characteristics within the main cha nnels but the dynamics are not well understood. Some research has take n place into meteorological conditions producing catastrophic flooding and into development of hydrological models using catchment variables . Much less is known of the properties and effects of flood waves with in channels, partly because of lack of records of these infrequent eve nts. It is not only water but also sediment which causes destruction i n floods, yet sediment is frequently ignored in channel management. Th e extreme conditions associated with floods in the region, the variabi lity of flows and of flood zones, the mobility of the channels and the high sediment loads create particular challenges for channel manageme nt. Trends in land use and channel management are tending to exacerbat e these problems. From this review it can be concluded that there is s till an important need for process-based understanding and modelling o f key soil erosion processes operating at a range of scales: i.e., fro m plots over hillslopes, catchments to regions. In particular, more re search is needed on the Linkages between upland areas which produce la rge volumes of runoff and sediment and channels on the other hand. Suc h linkages are through gullies and sedimentation zones. Monitoring and experimental data on key soil erosion and channel processes operating within Mediterranean landscapes are crucial for the improvement of so il erosion and channel models for a range of scales. In particular, lo ng-term monitoring of soil erosion processes and stream channel change s seems to be essential to observe the effects of infrequent torrentia l rain events on severe erosion, flooding and stream channel changes a s well as on the transient response of Mediterranean landscapes to cha nges in land use and climate. Systematic collation of historical evide nce of changes would be valuable. Implications of land and water use n eed to be examined in detail. A wide range of alternative strategies a nd techniques of channel and basin management must be explored and mod elled. A holistic approach to management of the fluvial system is reco mmended.