A STUDY ON THE MOTRU RIVERBED MORPHODYNAMICS WITH SPECIAL REFERENCE TO RIPARIAN QUALITY INDEX (RQI)

Ionuş Oana,University of Craiova, Romania

Abstract

The catchment area of the Motru river (S=1895 kmp, L=134 km) is located in the South-Western part of Romania and it is the biggest subbasin within the Jiu catchment area (direct tributary of the Danube river).
In the horizontal plan, the variation of the Motru river is caused by both morphological river bed processes, the transversal sections’ distortion (determined by the hydrological factor) and the instability degree salience, horseshoe bend migration (which is generated by the hydrological factor, the local morphology and the temporal evolution).
The main objective of the present study consists, on the one hand, in the achievement of a morphometrical database concerning the characteristics of the Motru riverbed, such as: the typological framing, the morphometrical variability, the dynamics registered at the cross section level; on the other hand, the study deals with the ecological status of riparian systems, through the Riparian Quality Index.
RQI is a useful tool for monitoring and evaluating the structure of riparian zones, based on: dimensions of land with riparian vegetation; longitudinal continuity; coverage and distribution pattern of riparian corridor; composition and structure of riparian vegetation and natural regeneration of woody species; bank conditions; floods and lateral connectivity.
The comparative studies of the cross sections made for the hydrometric stations (Cloşani, Târmigani, Broşteni and Faţa Motrului) underline the change of these sections through degradation and aggradation. The general trend that emphasizes the predominance of the degradation process is explained by the reduction of the alluvia quantity transported by the river and by the augmentation of the erosional power of the liquid flow.
Morphological river bank processes are obvious within the sectors where the river bed is characterised by a pronounced instability degree, marked by the concave and convex banks.
The research is based on relevant cartographic materials, the topographical map 1:25.000 (1975-1985) and the orthophotoplans made at the beginning of the XXIst century. Their further processing in GIS environment was checked and completed with the results of field study visits.
The importance of this study is to highlight the indissoluble link between the minor bed morphodynamic processes of bank and the Riparian Quality Index that provide a helpful criterion not only for the evaluation of the present status of riparian systems but also for formulating diagnosis and  selecting the rehabilitation options for such areas.