Recent geomorphological evolution of the deltas of the rivers Seman and Vjosa, Albania

Rising in the Neogene hills of the Mallakaster, the rivers Seman and Vjosa have built up two large joint deltas on the Albanian Adriatic shore. This s horeline is characterized by a low sandy coast with bars and spits. Changes in the river courses and migration of the mouths of the deltas were rapid and numerous from the Holocene period until the beginning of drainage works in the 1950s. The drainage basins of the two rivers are developed in soft elastic rocks (flysch and molasse) in the proportion of 71.4 per cent for t he Seman and 44.8 per cent for the Vjosa. Both rivers carry abundant sedime nt loads, amounting to 6.7 x 10(6) tonnes per year for the Vjosa and 13. x 10(6) tonnes per year for the Seman. This is the reason why the alluvial de posits of the Seman have built up two-thirds of the alluvial plain. The use of a SPOT image dated 25 May 1995 (HRV 3 081-268) enabled us to vie w the effects of coastal and fluvial dynamics, the role of neotectonics as well as the predominance of the plume of suspended sediment of the Seman ri ver. Using this image, a geomorphological map was drawn, which identifies t he palaeochannels of the Seman and the Vjosa. In order to date those palaeo channels we have made an archaeological inventory from oral and written pub lished information. The location of the sites we studied was checked system atically in the field. The mediaeval and Ottoman archives kept in Tirana al so provided substantial information, as well as the reconstitution of the e volution of the shoreline between 1870 and 1990, carried out using an inven tory of topographic maps. This work allowed us to reconstitute the progress ion of the deltas of the Seman and the Vjosa since antiquity. We may then infer that from antiquity up to the Middle Ages, the deltas of the Seman and the Vjosa both progressed very moderately and in a comparable way. However, at the end of the 15th century the Seman underwent a major c hange in its course, through a southward migration of the river. The natura l processes of alluviation and changes in the river courses seem to have be en accelerated as agricultural exploitation of the Neogene hills that form most of the drainage basin of the Seman increased. This exploitation is lin ked with the massive exportation of cereal from the port of Skela e Pirgut, which started in the 14th century. It appears that the 20th century has be en the period of the largest progression of the deltas during historical ti mes. The speed of progression increased as early as the beginning of the ce ntury, as a result of the rapid growth of the rural population densities. S oil erosion from arable fields increased catchment sediment yields to promo te rapid changes in the river courses. This resulted in abandonment of delt aic mouths, a phenomenon leading to a straightening of the coast. Thus to t he south of the present mouth of the Seman the coast receded by 7 to 30 m p er year between 1968 and 1990 as a result of the abandonment of a mouth. Co pyright (C) 2001 John Wiley & Sons, Ltd.