After a 16-m high dam was constructed and a 297-ha pond was arranged in the River Šušvė nearby Angiriai in 1980, the previous natural flow regime of the river has changed: 15500000 m3 of water accumulated above the dam is not discharged via a natural bed, but through two 1.5x1.5 m bottom orifices, and flood discharges (up to Q1% = 296 m3 sE-1) are directed into the lower reach through a 16-m high shaft spillway of floods. Such arrangement of the Angiriai dam ensured it to become an essential obstacle for migrating fish. In 2000, after the arrangement and operation of Angiriai hydro-electric power station, the water regime downstream the dam has been changed and new hydrological pulses as well as ecosystem biodiversity are to be adapted. Thus, the operation of Angiriai HPS on the River Šušvė generating hydroelectric power can have adverse effect on the river habitats and hydro ecological connectivity. To evaluate the effect, the eco-hydraulic water regime measurements in 2005 in a lower stretch with and without turbines operating were made. The study results showed that artificial water levels fluctuation (≈ 4 m hrE-1) induced by Angiriai hydro-electric power station as well as the discharge flowing through the bottom orifices due to high velocities (13–14 m sE-1) and temperature differences could create stressful situations for young fish in the lower bank. According to the data of soil texture of the Šušvė River, the bed armoring process is going on below the Angiriai HPS is quasistable and no impact of HPS operation is found.

Due to the recently increasing frequency of extreme changes in river runoff regime, scientific literature deals with the characteristics of runoff formation. Works are carried out in analyzing climate changes and a lot of attention falls on land–use structures. Following thorough analysis of the lithological structure of river basins in separate costal zones, this article aims at evaluating river runoff formation characteristics. The basin lithological factor was calculated based on Quaternary map of Lithuania M 1:200000 and Lithuanian river map M 1:50000 using ArcGis software. In order to carry out more thorough analysis of the influence of lithology in given territories, sections of 0–20 m, 50–200 m, 200–500 m, 500–800 m, 800–1000 m and is greater than 1000 m were established, calculating the distance in meters from the riverbank. Eight river basins of typical lithological structure (sandy, loamy, argillaceous) were selected and examined. The period of the years 1960–2007 was analyzed as this period saw the greatest amount of precipitation (up to 33% probability), and relation between the runoff and precipitation was established as well as that with the lithological structure, established following the derivation of a hydromodule.

Most of the regulated rivers are situated in the middle part of Lithuania. Approximately 90% of all agricultural lands are drained in the Basin of Nevezis River, which is one of the most sensitive basins in Lithuania due to the lack of water and potential anthropogenic pollution. The goal of the research is to assess the impact of drainage on Nevezis River flow. Following the data series of 62 years, it was determined that water balance of Nevezis Basin is characterized by negative water balance during May-September due to higher evapotranspiration than average precipitation amount of the same period. It was stated that the average annual flow coefficient of the whole 10th hydrologic region of Lithuania was 0.3 till reclamation. It decreased to 0.28 during the period of intensive reclamation; however, the average annual flow was 0.35 from the year 1980, i.e., it increased in comparison with the period till reclamation. The average flow coefficient of warm period was 0.10 till reclamation, and remained the same during the period of 1956-1980, while the data of 1981-1995 show that the average flow coefficient increased – 0.11. After assessing the meteorological conditions and soil water balance of the Basin of Nevezis River it might be stated that the primary reason of water lack in the basin is climatic conditions. Drainage systems can hardly have a significant impact on wateriness of Nevezis River.

Kriging is a method of interpolation, which predicts unknown values from data observed at known locations. This method uses a variogram to express spatial variation, and it minimizes the error of predicted values which are estimated by spatial distribution. The objective of the current work was to investigate how the accuracy of predicted runoff average depth values ranges by applying ordinary Kriging interpolation method when parameters of the method are altered. The simulation was tested by the following method parameters on: fitted semivariogram model, lag size, neighbouring points; the number of sectors of the circle. The best results of the spatial distribution of runoff average depth were received applying the ordinary Kriging method when the exponential variogram is used, the lag size being 27 km while 6 contiguous points and the orbicular scheme divided into sectors in 45° angle are taken. Applying the Ordinary Kriging method having selected all parameters with probability p = 0.95 the model described about 74% of all investigated values.

In this study, a conceptual rainfall-runoff METQ model, version METQ2007BDOPT, to simulate daily runoff was applied. The model structure and parameters were fundamentally the same as in the METQ98 model with some additional improvement and semi-automatical calibration performance. The model has proved to be successful for both small (the Vienziemite Brook, 5.92 km2 ) and large (the Daugava River, 81 000 km2 ) drainage basins. The model METQ2007BDOPT was calibrated to the six different size river basins (the Pērse, the Malta, the Neriņa, the Imula, the Malmuta and the Iecava). These pilot river basins are characterised by one or two prevailing natural conditions such as hilly agricultural lands, agricultural lowlands, sandy lowlands, forested areas, swamps or lakes. The results of calibration showed good coincidence between the measured and simulated daily discharges. The Nash – Sutcliffe model efficiency coefficient NSE varies from 0.52 to 0.78 and Pearson correlation coefficient r from 0.65 to 0.88 for the six river basins with calibration and validation period from 1956 to 2015. In this study, we found some relationships between the model parameter values and physiographic sub-catchment characteristics.

This study is important to contribute morphometry researches and give an example of how to accomplish studies about lakes. The aim of the study is to use the latest technology to determine the morphometric parameters and their variability compared to the previous research results. Research focuses not only on local water body morphometry and bathymetry, and their influencing factors, but also deals with methodological issues regarding measurements of morphometric characteristics and data interpretation as well as state of the art visualization of results. On many occasions, there is a lack of research on morphometry of water bodies or they have taken place in the last century, which has led to the use of obsolete research methods in modern morphometry studies that do not produce the results of a high level of detail. The aim of the study is to use the latest technology to determine the morphometric parameters and their variability compared to the previous research results. The study consists of analysis of the literature on morphometry, methodology used in bathymetry studies, history of research, research methods used in the previous studies. The research object is Lake Kisezers including its morphometry, bathymetry, and influencing factors. The results of the study show that morphometric parameters of Kisezers differ from the results of previous studies. The results of the study confirm that Lake Kisezers is exposed to various influencing factors, mainly anthropogenic. The main factor influencing morphometry and hydrological regime in Kisezers is the water level fluctuations influenced by Riga Hydroelectric Power Plant.

The urbanization and increasing growth of planet’s population accumulates significant volume of disposed waste as well as increases risks on human health and environmental safety. Landfill systems are the dynamic, living in space and time, potentially harmful entities that must be managed in as careful and smart way as possible. There are many studies related to landfill emissions such as leachates and methane. However, there is a need for advanced understanding of landfill hydrological regime and risks related to climate change and associated changes of hydrological cycle. The comprehensive studies about the urban hydrology are available; however, application to landfill management is fragmentary and inconsistent in several aspects. Landfill in long term has an impact on hydrological cycle. The heterogeneous land surface is one of aspects; however, there are still unanswered questions about the urban environment impact on water balance components. The aim of this study is to describe fundamentals of landfill hydrology in urban hydrological response unit context as well as evaluate the potential risks to environment and human health related to landfill geomorphology and hydrological balance in temporal climate conditions. The landfill hydrological cycle has similarities with urban hydrological cycle; however, there are additional components related to landfill specification, e.g., irrigation or leachate recirculation as well as total produced leachate.

The aim of the paper is to determine the relationship between meteorological drought and hydrological drought in the agricultural basin of the River Osa (northern Poland) in the years 1966-2015. Meteorological droughts appear as a result of insufficient amount or lack of atmospheric precipitation. As a consequence of meteorological droughts occurrences, there appear hydrological droughts which are characterized by low discharges of a river. Standardized Precipitation Index (SPI) and Standardized Runoff Index (SRI) indicators were used for the identification of droughts at various accumulation periods, i.e. 1, 3, 6, 9 and 12 months. In the years 1966-2015, there were identified from 63 (SPI-1) up to 10 meteorological droughts (SPI-12), while hydrological droughts – from 22 (SPI-1) to 8 (SPI-6, 9 and 12). The strongest relationship between the two kinds of droughts occurred in the periods of accumulation from 9 to 12 months. The values of the correlation coefficient between the meteorological and hydrological droughts were above 0.5 in those cases. Those indicators can be used for a system of early drought warning, which is of particular importance for crop production in agricultural areas. Long-lasting meteorological droughts contribute to increase of water intake for irrigation purposes, thus deepening the hydrological drought. As a consequence of the prolonged and intense hydrological drought, further irrigation may be impossible due to too low river discharges.

Peat is still mined in many parts of the world for production of peat substrates and energy. Many peatlands were affected by drainage in the past also for forestry and agricultural needs. Nowadays a raised attention to peatlands is focused, especially to drained peatlands due to their carbon reserves and their potential influence to the climate on the one hand, but on the other hand - due to raising awareness on protection of environment, habitats and biotopes. There are many examples on restoration activities in peatlands found worldwide, especially their water regime is the subject of regulation, which plays the major role to bring back original functions. In most cases in Latvia as the aim for protection and restoration of degraded peatlands was protection of EU biotopes and habitats. Of course, peatlands play an important role in emissions of the greenhouse gases CO2, CH4 and N2O, produced during mineralization of the drained peat organic matter. In literature, we can find only few cases where hydrological regimes are described for natural raised as well as restored block-cut peat extraction fields. This research analyses block-cut peat extraction field water level fluctuation influence on naturally raised bog hydrological regimes. Hourly data is analysed for six groundwater monitoring wells as well as for determination needs of water level fluctuations in excavated peat quarry as a response to precipitation.

In the world, hydrological models are often used in the modelling of ecological components. In the context of the Paris Agreement and the European Green Deal, it is necessary to develop GHG emission modelling capabilities. The development and refinement of the conceptual model METQ is necessary not only for the quantitative analysis of flow, but in addition to its refinement, it is possible to conduct interdisciplinary research in the subfield of ecohydrology, which studies the interaction of water and ecosystems, and in environmental engineering, which addresses the issues of reducing diffuse pollution and reducing greenhouse gas emissions, technology implementation issues, where water content in the soil and groundwater fluctuations play one of the main roles, for example, in the processes of the formation of nitrous oxide emissions. This paper examines potential GHG emission calculation algorithms used to successfully model GHG emissions from soils, with a particular focus on agricultural soils, which contribute one of the largest amounts of GHG emissions in national emission reports for the agricultural sector. Available algorithms for nitrous oxide nitrification calculations are reviewed and possible algorithms that can be used for modelling emissions from soils and integrated into the conceptual hydrological model METQ are discussed. The developed conceptual solutions for modelling GHG emissions from soils will develop a modelling tool that will be used to estimate the volumes of GHG emissions and evaluate the effectiveness of various GHG emission reduction measures, as well as to perform a complex assessment of the soil GHG balance.