Hydrological characteristics of the Drava river in Croatia

Abstract

The Drava River is one of the biggest right-bank tributary of the Danube and one of the most important rivers in continental Croatia. Its great environmental value is in conflict with its economic potential in hydroelectricity, navigation, and irrigation. During the history, many hydraulic structures were constructed on the river and caused changes in its hydrological regime. In addition, in the early 1980s, climate change manifested in less precipitation and higher air temperature became more evident. A hydrological analysis of the Croatian section of the Drava River pointed out the consequences of both trends. There are three different sections of the Drava River: • the upstream section dependent on dam constructions; • the middle part affected by the tributaries and • the lower section under the influence of the Danube River backwater. Analyses of water level and discharge time series between 1960 and 2015 were made for five hydrological gauging stations in Croatia. All characteristic minimum, average, and maximum values of these two parameters have shown a decreasing trend with two exceptions in the most upstream part of the river where three dams were constructed. Extreme hydrological events, floods and droughts were also analyzed. High water levels, which were a great threat in the past, are better controlled by dykes today, but they still endanger the area along the confluence of the Drava and Mura and the lowermost section due to the backwater effect of the Danube River. Droughts or periods of low discharges are becoming a more and more serious problem in the last 15 years, but, according the standardized streamflow index for detected drought severity, there is no clear increasing trend in drought frequency.