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IMPACT OF THE RIVER LEVEL REGIME ON THE GROUNDWATER DYNAMICS AND PHYSICOCHEMICAL CHARACTERISTICS OF THE ALLUVIAL AQUIFER IN THE OGOSTA VALLEY

Peter Gerginov

Abstract

In relation with a study of arsenic pollution of groundwater in the Ogosta Valley, NW Bulgaria, a monitoring station was built in the floodplain in the upper reaches of the Ogosta River, not far from the town of Chiprovtsi. The observations took place at three adjacent sites including a hydrometric river gauge and two tube wells located closer and further from the river. River stages, groundwater level, water temperature and electrical conductivity were measured automatically at the three sites. Water pH, dissolved oxygen and redox potential were measured also in the well situated closer to the river. Collected data for a period of one year was statistically processed and major statistical characteristics were obtained. A relationship between the observed parameters was found and used to characterize the impact of river flow dynamics on the quantitative and qualitative indicators of groundwater. The delay of the groundwater level response to the fluctuations of the river stages was determined. An assessment of the impact of high river flow events on the magnitudes of the observed physical and chemical indicators was made. The results provide a better insight into the water fluxes within the river-floodplain system and into the conditions for arsenic migration in the aquifer in the Ogosta Valley.

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