Impact of Ice Regime in the Nemunas River and the Curonian Lagoon on Floods in the Delta Area

The main River Nemunas of Lithuania with the length of 937 kilometers drains the area of 98.100 square kilometers having the mean runoff module of about 6.6 l/s per square kilometer. The river drains the NW part of the North Belarusian Plain as well as it collects water from a hilly and laky Lithuanian plain. Then it enters the Curonian Lagoon, which is a transit basin on the fresh water way to the Baltic Sea. The climatic conditions within the area depend on the solar radiation and the circulation of the atmospheric air masses usually moving from the West to the East. In winters the River Nemunas is usually covered with ice. In previous decades about 40% of the river runoff was usually observed during the spring floods ( from February to April). During the extreme spring floods the water level can reach the height of even 8 meters above the 0 level with the sequent flooding of living areas and agricultural fields in the lowlands. The most important and dangerous phenomenon to mention is the occurrence of rather frequent flood events in the lower part of the river. The tendency is evident by analyzing the available level-gauge data of the River Nemunas that have been reported since 1812 from Smalininkai river level gauge, situated 112 km up from the river mouth. Moreover, during the recent decades the major changes in the river hydrological regime have taken place as a result of significant changes in climate. The intention of this study is to analyze the long-term observations of river level runoff and ice regime data in Smalininkai and data of the water level and ice regime in Nida hydrological station, situated on the shore of the Curonian Lagoon. The aim is to find the relationship between the fluctuations of the mentioned parameters and the readings of flood water level on winter and spring with the prediction of situation in the river Nemunas Delta that stretches within the area of approximately 2200 square kilometers as well as in the Curonian Lagoon.