PROCESSES RESHAPING THE EBRO DELTA

Due to the limited supply of sediment from the Ebro river, its delta i s mainly subject to reshaping processes in the form of alongshore alte rnation of erosive and accretive coastal stretches, without a signific ant change in the overall subaerial surface of the delta. The main age nts presently forcing these processes (waves and mean water-level osci llations) are analysed in detail as a function of their contribution t o coastal processes. In this manner, waves are characterised in terms of short-term/seasonal changes, longshore sediment transport pattern, long-term cross-shore transport at the shoreface and storm impacts. Al though the study area is a microtidal one, and waves are the main agen t forcing coastal evolution at yearly scales, mean water-level oscilla tions (meteorological tides and long-term relative mean sea-level vari ations) play a non-negligible role. Additionally, a joint analysis of waves and storm surges has been done in order to characterise conditio ns inducing an 'impulsive' type of coastal response. At last, the clas sical ternary classification of deltas has been applied in a 'dynamica l way' by considering the river vertex in terms of the variation in se diment supply. Moreover, the effects of considering mean water-level v ariations (other than tides) on the deltaic classification has also be en tested. The inclusion of RSLR influence becomes relevant for 'river -independent' deltas since it indicates the inability of the delta to withstand it. The main problem to include this agent in the ternary cl assification is that RSLR is more of a 'passive' factor, whereas the o ther considered agents are 'active' in the sense that they induce more perceivable morphological processes. (C) 1997 Elsevier Science B.V.