Fluvial geomorphology of the Kupa River drainage basin,Croatia: A perspective of its application in river managementand pollution studies

摘要

This paper aims to describe for the first time the geomorphology, tectonic setting, lithological framework and granulometric properties of the transboundary Kupa River basin of Croatia, Slovenia and Bosnia and Herzegovina, situated at the very south of the Danube River basin. The generally meandering, east to west running course of the Kupa River starts from a karstic spring in the mountainous region and flows down to the plains with braided channels, particularly at points of outfall of a large number of tributaries joining both from the north and the south. Belonging to the seismically active terrain and Adriatic carbonate platform, the geo-morphic aspects of the river catchments, channel patterns and deposition-erosion processes are significantly controlled by seismicity related faults and thick carbonate succession of karst in Dinarides. The river borne materials vary widely in size from boulders to fine sand, the miner-al compositions of which are derived from the metamorphic and sedimentary rocks. The grav-elly marginal bars and channel bars are quite common at the upper reach of the river whereas, sandy point bars characterize some locations of inner meander bends. The gravelly channel-lag deposits and exposed bed rocks often hinder the streamline flow of the river during the low wa-ter level in the summer months. Flow separations together with very sluggish back flow against bed rock barriers cause distinctive differences in flow patterns and flow velocities in many places along the course of the river. The calculated grain size parameters were used to evaluate the model of Mc LAREN (1981). It was found to be in agreement with our results, that sediments became finer and more positively skewed in the direction of transport. During the summer months, this potentially resourceful river is getting locally moribund and arrested within its course due to fall of river level and extremely uneven bed level configuration along both trans-verse and longitudinal profiles of the river. Influx of pollutants and their restricted circulation in many places have led to severe eutrophication with macroalgal blooms and generation of marsh vegetation,. Human interference by construction of weirs for hydroelectrical power plants, construction of embankments for bank protections together with stacking of rock boul-ders on river bed for angling, dredging and mining of river bed in some places has further caused modifications to the morphology, morphodynamics and grain size characteristics of the river channel. Contamination from barite mine tailings, agriculture, industries and sewage waters has attained an alarming state on some stretches. The authors have suggested the need for system-atic monitoring of the Kupa drainage basin, especially in terms of its channel patterns, tectonic geomorphology and hydro-meteorological control, in addition to pollutants in sediments and waters, and thus to understand past environment and future changes.