Effect of Rushes on Evaporation Rate in Water Reservoirs on the Example of Powidzkie Lake

This paper presents research on evaporation from the lake surface within the reed bed zone. The main focus of the research was the process of evaporation of water adhered to reed culms in different weather conditions. The process of transpiration, i.e. evaporation of water from plants due to their physiological processes was ignored. To avoid any ambiguity and to stress the different nature of both processes, the studied phenomenon is referred to as “mechanical evaporation”. The analysis was based on measurements taken on Powidzkie Lake. The results showed that “mechanical evaporation” from reed culms above the water level can considerably increase evaporation rate of an aquifer. The values of total evaporation within the reed bed zone were estimated. These were compared to the values of evaporation from the open lake surface. The rate difference was at the level of 10–30%. Furthermore, the study showed that the value of “mechanical evaporation” varied depending on the reed species, wind speed and direction, wave height, and width of lakeshore with vegetation. Seasonal variations of the lake's water surface were of slightly lesser importance.