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The main object of the paper article is water resources of Lithuanian rivers, which were calculated using a long data series of the runoff. Water resources are based on the balance equation. This means that this equation includes only the runoff formed in the Lithuanian territory, from neighboring countries to Lithuania and through them into the sea. The average and dry annual water resources have been calculated at a 95% probability. The average perennial water resources of Lithuanian rivers are 24.844 km³ / year, of them 8.883 km³ / year is the transit from Belarus, Poland and Kaliningrad Region to Lithuania, 15.961 km³ / year is formed in Lithuania and 7.471 km³ / year are effluents through Latvia into the Baltic Sea from Kaliningrad Region into the Curonian Lagoon. The Nemunas basin floats 21.501 km³ / year to the Curonian Lagoon. The present water resources are by 4.5% less in comparison with water resources of in the year 1996. Cyclic water change is typical of the Lithuanian rivers. The Nemunas-Smalininkai hydrological station has noted 7 cycles in a long data series. The average term of a cycle is 27 years (14 years of a wet and 13 years of a dry period). The runoff of the Nemunas river differs in the duration of dry and wet periods (by about 16%). The runoff of rivers in Southeast and Western Lithuania differs by 21-23% and in Middle Lithuania by 28%. The long data series of the Nemunas-Smalininkai runoff have a negative trend because of a decrease in the last four decades. The runoff measured by this water management station consists of river runoff from the southeastern and middle parts of Lithuania. The annual runoff has a positive trend in the majority of Western Lithuanian rivers in the period 1961-2003. The minimum runoff of a dry period shows no trend in most Lithuanian rivers, except Western Lithuania where a positive trend was estimated in the period 1961-2003. [ABSTRACT FROM AUTHOR]

The main parameters (flood duration, runoff volume and maximum discharges) of spring flood change over time. A review of the characteristic of spring floods in Lithuanian rivers and the distribution of the different parameters is presented. The objectives of the current research were the following: assessment of spring flood parameters in a long period for three hydrological districts of Lithuania and trends of spring flood volume change, spring flood peak and spring flood timing during three periods (1922-2003, 1941-2003 and 1961-2003) using the Mann-Kendall test. Daily discharges from 32 water measurement stations (WMS) were used for this research. Data were analysed for the above three periods (methods of the project "Climate and Energy"). Mann--Kendall tests were carried out for the runoff volume, maximum discharge and spring flood timing trend analysis during the three periods. In the period 1961-2003, in all Lithuanian territory there were no trends of flood runoff alternation. It means that flood runoff on average was stable. The situation was the same also in the period 1941-2003. There are no trends in all Lithuanian territory, i. e. the runoff is stable from the point of view of average runoff. Only a long data series (1922-2003) showed that flood runoff had been decreasing in Southeastern Lithuania where WMS had negative trends, i. e. flood runoff volume was decreasing. The tendency of change of maximum discharge dates is similar in all hydrological districts. Everywhere the trends are definitely negative, i. e. the maximum discharges are observed earlier and earlier (because of warmer winters). Positive trends were observed in the change of maximum discharges in the period 1961-2003 in rivers of Western Lithuania, i. e. discharges were increasing. In Middle and Southeastern Lithuania, rivers had negative trends during all the three periods, i. e. the maximum flood discharges were decreasing. [ABSTRACT FROM AUTHOR]

The object of research of Lithuanian engineering hydrology today is regime alterations of rivers caused by climate warming, determination of the environmental impact of the activities of large industrial and transport facilities and substantiation of environmental safety measures. The main tasks at this stage are: --evaluation of changes in river runoff caused by climate variation; --evaluation of exploitation risks of hydrotechnical structures; --investigation of the hydrodynamic regime of the Klaipėda Strait and the Baltic Sea with the determination of the impact of the industrial development of the sea-port on the environment. For solving these problems, new data processing and process modeling methods are applied. It was established that the runoff characteristics of the Lithuanian rivers reveal the following trends: then annual runoff and the maximal spring flood flow rates decrease while their winter runoff increases. The scenario analysis of disastrous failures of the Kruonis Pumped Water Power Plant showed that a danger to the city of Kaunas can be caused only by an accident coinciding with a flood of the catastrophic scale. The results of hydrodynamic modeling of the Klaipėda Strait enabled to determine the limit conditions of the seaport development and industrial expansion and to recommend the means of environmental protection. [ABSTRACT FROM AUTHOR]