Assessment of the impact of anthropogenic activities on the flow of the river Vilnia basin

Abstract

River flow is one of the most important links of the water circulation in the nature which describes general water yield and potential water resources of a river basin. Since the range of the flow change is best illustrated by very long-term data of water measuring stations that include flow measurement sequences and the Lithuanian Hydrometeorological Service is carrying out hydrological observations of the river concerned in one spot- in Vilnius, at the point before Vilnia flows into the river Neris - this data is not enough in order to assess the distribution of the river flow before the pond (potential anthropological impact on the flow) and after it. During the investigation, water level was being measured in selected measurement points of the river. According to measured water levels average monthly debits were derived and coefficients closely related to the measurement points were calculated. Recalculated average monthly debits for the sequence of 1993-2009 have showed that the biggest leap of the flow occurs between points 1 and 2; sudden increase of the flow of this section was influenced by the pond Margiai. In spring, water which is collected in the pond after the snowmelt is released in small quantities to the river Vilnia. Distribution of the flow is most distinct at the end of limiting seasons. The most sudden changes occur in the months of April-May and August-September.