The Role of Lakes in Shaping the Runoff of Lakeland Rivers

Hydrological functions of lakes in shaping the runoff of rivers that drain them were discussed on the basis of data from the literature. The discussion indicates the role of lakes in initiating river runoff, their role in water storage and runoff equalization of a river flowing through or out of the lake, as well as the role in shaping the runoff capacity of the river: its increase due to underground water drainage by the lake basin or decrease as a result of lake waters supplying the underground water. It was pointed out that there are lakes which regardless of the character of the hydrological year (wet, average, dry) constantly increase the runoff of the river which flows through them by incorporating into it the water which they receive from underground drainage. There are also lakes that constantly feed underground waters with their waters, which reduces the runoff of rivers flowing from them. There is also a group of lakes which, depending on the level of the storage of the basin, conditioned by the water content of the hydrological year, either drain underground waters and increase river runoff or aliment them thus reducing river runoff. The above hydrological functions of lakes were discussed on the example of outflow and flow-through lakes of northern Poland.