Polish Rivers as Hydrographic Objects

This paper characterises rivers, the major hydrographic objects within the water network of Poland. The authors point out to the diverse nature of the river network resulting from the natural topography of Poland and the fact that the contemporary river network uses valleys inherited from the past. Systems of two largest Polish allochthonous (transit) rivers, the Vistula and the Oder, are characterised. The rivers of Przymorze and the Niemen basin are discussed in less detail. The paper shows that the stability of discharge in Polish rivers, resulting from climate conditions (precipitation exceeding field evaporation over the entire water year), is determined by the underground contributor to the discharge, which is a result of underground water drainage by the river channels. The contribution of underground runoff to the total discharge of Polish rivers is generally stable over the year, and the percentage of surface runoff contributing to the total discharge depends on the morphogenetic zone (mountains, highlands, lowlands) where these rivers flow. Finally, the types of regimes characterising Polish rivers are presented and their spatial differentiation is discussed. Polish rivers are characterised by complex regimes. Most rivers are characterised by the moderately developed nival regime with the high water period in the spring. Some of the lowland rivers have well-developed nival regime, while some lakeland rivers are characterised by the poorly developed nival regime. The regimes of mountain rivers vary.