ABSTRACT. - Human-induced Modifications in the Dipşa Hydrographic Basin . Any engineering inducing channel- bed change has an impact on river water regime and sediment transport by land use, channel regulation works. Intensive human interventions (meander cut, embankment and chennalization) meant to reclaim agricultural land and prevent the alluvial plain from overflows, have affected the Dipsa River channel morphology. The purpose of this study is to analyze the degree of man- induced river-channel changes (adjustments after engineering works), taking into account river-bed morphometrical and hydrological parameters. This study used pre- and post-channel regulation data of some engineering projects initiated in 1977, statistically analysed. The morphological features studied were planform configuration, channel width, mean depth, maximum depth, river-bed and the width-depth ratio. Channel planform change was investigated using the rate of channel sinuosity change in the selected sectors by overlaying information from historical maps (topographical plans 1:5 000) by GIS techniques. Cross-section transects 1:100 allowed the reconstruction of the magnitude of channel bed changes. Based on river thalweg levels we could trace the longitudinal profile of the study area, highlighting the general descending trend of the river bed. These changes in channel morphology severed the stream from its floodplain, decreased sinuosity, and homogenized stream profiles. The results indicate that the Dipsa River morphology has been widely changed by human interventions, compared to its initial aspect. To see if the anthropic impact affected the hydrological parameters, we analysed the monthly data (pre-and post-channel regulation) of medium and maximum discharge,and of sediment discharge and made an assessment of the evolution of peak flows and damages in order to estimate the efficiency of the project.
Key-words: channel change, regulation, GIS, human impact.