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Over a period of 30 years, the surface water level in the north-west of Konin, in the east of the Wielkopolska region, decreased by almost 6 m, resulting in a reduction of the surface area of the majority of nearby lakes, the disappearance of smaller water bodies and wetlands, and the drying out of streams draining the area. The causes of the decrease in the surface and groundwater level in the region are complex. They include both natural and anthropogenic factors, among others broad-scale mining activity. Based on knowledge of the hydrostructural composition of the analysed region and the functioning drainage system of opencast lignite mines, a concept was developed of a change in water supply to the flooded opencast lignite mine, Kazimierz Północ. The task of redirecting waters from the drainage of a nearby opencast mine, Jóźwin IIB, was implemented in 2020. Current observations and forecasts suggest that, owing to the applied solutions, the analysed opencast mine will be flooded in 2023, and not, as previously assumed, at the end of 2021. As a result, groundwater levels in the vicinity of the opencast mine as well as in lakes and rivers within the range of impact of the related depression cone will be restored faster, particularly in the Lake Powidzkie catchment. The objective of the study is to present stages of flooding of the former opencast lignite mine Kazimierz Północ, identify factors determining the process, and describe solutions accelerating it, with a simultaneous environmental impact assessment of the undertaken activities. [ABSTRACT FROM AUTHOR]

Changes in nutrient concentrations in groundwater were investigated to determine the impact of agriculture on water quality in artificial lakes. The study covered three reservoirs in an agricultural area of Wielkopolska (central-western part of Poland). Assessing the agricultural impact required a network of piezometers around the reservoirs, used to determine the degree of groundwater pollution from nutrients supplied to the reservoirs. Moreover, the analysis covered the quality of water in streams flowing into the reservoirs, and in the reservoirs themselves. Field research was conducted every month of the growing season from March to November. The analysis covered land inclination, ground permeability, and soil type. Detailed objectives included: (1) assessment of the agricultural impact on the chemical parameters of ground and surface water quality, and (2) evaluation of the impact of different sources of agricultural pollution on water quality in artificial reservoirs in regards to their management. This study revealed high dynamics of nutrient concentrations, particularly for nitrates and phosphates, in groundwater and surface water. A significant effect of maize cultivation on an increase in nitrate concentrations in the groundwater of the catchment of the Przebędowo Reservoir was evidenced, as well as a substantial effect of the functioning of an animal farm on the quality of groundwaters in the catchment of the Lachotka Reservoir. The nutrient load of agricultural origin in the catchment of the Miedzichowo Reservoir was relatively low. Our study revealed elevated amounts of nutrients such as nitrogen and phosphorus, detected more frequently in groundwater than in running waters, which confirms our hypothesis of the importance of groundwater analysis in detecting the source of pollution of the studied lakes. High nutrient concentrations recorded in groundwater leached from arable fields were also observed in the summer period, failing to confirm the hypothesis that the greatest effect of factors would be related to the spring effect of arable fields on water quality (lack of compact vegetation cover, high water level, etc.). Our study also indicated a greater importance of the type of land use than lithology or permeability of deposits. [ABSTRACT FROM AUTHOR]

This paper presents the impact of flow changes in the Warta River and water management rules regarding the Jeziorsko dam reservoir on the energy production by the hydropower plant in the period 1995–2021. The Jeziorsko dam reservoir was built in 1986. It is the second largest dam reservoir in Poland in terms of surface area. In 1994, a hydropower plant with an installed capacity of 4.89 MW started operation. The study results show the average annual energy production from 1995 to 2021 at a level of 18,718 MWh. On the other hand, energy production largely changed from year to year, from 12,432 MWh (in 2019) to 26,916 MWh (in 2001). The droughts that have occurred in the Warta River basin over the past two decades have had a major impact on energy production. As a consequence of the drought, it was not possible to maintain the required water level in the reservoir. Moreover, a change in the rules for the reservoir's management that led to lower water levels in the reservoir by 1.5 m between April and June was important from the point of view of energy production. Improving the efficiency of energy production requires changing the rules of water management in the reservoir. More flexible reservoir operation schemes should be considered, including operational management based on meteorological and hydrological forecasts. Moreover, other criteria should also be considered, such as maintaining environmental flows, ensuring protection from flooding, and operating a nature reserve around the reservoir. [ABSTRACT FROM AUTHOR]

The progressing development of civilisation and climate change require access to an appropriate quantity of environmental resources. One of the key resources is water. Both its deficit and excess evidently affect human life. Control over water circulation is possible owing to water management, largely involving introduction of hydraulic structures. The paper analyses the effect of the Jeziorsko dam reservoir on the flows of the Warta River, the third largest river in Poland. It analyses water flows in the Warta River in the years 1993–2020 for hydrological stations above and below the reservoir. The conducted research showed that the construction of the Jeziorsko reservoir also substantially contributed to an increase in minimum flows and a decrease in maximum flows. Moreover, the simulation showed that in the case of abscence of the reservoir, the flows of the Warta River would be higher in the period from January to June, and in the period from July to October the opposite situation would occur. In November and December, the flows would be at a similar level. Results obtained in the study, show that hydraulic structures are an effective solution in the context of stabilisation of the hydrological situation in a given region, particularly in terms of hydrological lows occurring with increasing intensity mitigated on sections of rivers below the reservoirs. [ABSTRACT FROM AUTHOR]

Successively conducted monitoring and inspections allow for the detection of emerging issues and their elimination. The objective of this study is the analysis of the administrative procedures related to the monitoring of the technical condition of small hydraulic structures in Poland. The case study of the Oświecim Weir on the Prosna River presents the parameters subject to assessment and further activities aimed at the elimination of the detected defects. The obtained results showed damage to its concrete structures, including cracks and cavities. The undertaken activities related to the complete remodelling of the Oświecim Weir and the incurred costs generally result from the environmental conditions (water flows in the Prosna River), directly causing the necessity for the stabilisation of water conditions in the area. In the context of the observed climatic changes, the problem is faced by more and more regions around the globe. The proper technical condition of hydraulic structures, resulting from diligent monitoring, provides the basis for the mitigation of this unfavourable situation. [ABSTRACT FROM AUTHOR]

Poland is among the European countries with the lowest water resources. The central part of Poland features the least water resources in the country. In this region, proper water management is particularly critical to maintaining high agricultural productivity. The objective of this study was to present the effects of the restoration of hydrotechnical infrastructure in the Rgilewka River catchment in the zone of the greatest water deficits. This paper analyses the effects of such works on water resources and their management. The catchment featured seven weirs in 2014, all built in the 1950s. Due to the lack of maintenance and ongoing renovation, they have lost their basic functions. In 2014, modernisation of the system commenced by rebuilding all the existing weirs. Two new weirs were also constructed. The work was completed in 2021. The currently existing weirs provide greater water retention and management capabilities. The direct impact of weirs ranges from 1.9 to 3.5 ha, their indirect impact from 34 to 70 ha, and the river channel retention varies from 2200 to 5400 m3. Total water retention in the Rgilewka River channel due to the modernisation of hydrotechnical infrastructure reaches 25,400 m3. The direct (total) impact range will cover an area of 16.4 ha, and the indirect impact range an area of 284 ha. [ABSTRACT FROM AUTHOR]

Changes in water levels in lakes play an important role in the development of their coastal zones and water trophy. The aim of this study was to assess the role of changes in hydrometeorological conditions in the development of littoral and riparian vegetation of a meromictic lake during the last half-century. The study was carried out in Lake Powidzkie, one of the largest water reservoirs located in central Poland. Water level and meteorological conditions were analyzed in the period 1961–2015. Modifications in the range of plant communities were analyzed on the basis of cartographic materials and field studies. Meteorological conditions, especially precipitation and evaporation, were found to strongly affect the lake's water retention, whilst they had less of an effect on water levels. A significant effect of the lowering of the water level in Lake Powidzkie on the development of the littoral zone, whose area more than doubled over the last half-century, from 41.5 to 118.8 ha, was noted. The most dynamic development of the littoral was observed in the last quarter of the century, in which three of several years of low-flow were recorded. The occurrence of periods with an increased amount of precipitation, after dry periods, did not contribute to the reduction of the size of the rush zone and limitation of the development of woody vegetation. [ABSTRACT FROM AUTHOR]

The study evaluated the effect of environmental conditions and morphometric parameters on lake water temperature changes. The analysis was carried out on the basis of 14 lakes located in northern Poland. The assessment was based on the daily water and air temperatures from 1972 to 2016. It took into account the location of lakes (latitude, longitude, altitude) morphometric parameters (surface area, maximum and mean depth, volume), hydrological processes (rate of water exchange, course of ice phenomena), and trophic status (water transparency) as factors that can modify lake water temperature changes. Direction and rate of air and water temperature changes were analysed by means of Mann–Kendall’s and Sen’s tests. Cluster analysis (CA) was applied to group lakes characterised by similar water temperature changes. The effect of climatic and non-climatic parameters on a lake’s water temperature was assessed on the basis of principal component analysis (PCA). Water temperatures in the lakes in the years 1972–2016 were characterised by a higher rate of increase of 0.43 °C·dec−1 than the air temperature decrease of 0.34 °C·dec−1. The analysis showed a faster rate of heating of waters in western Poland. This can be explained by shorter duration of ice cover. Moreover, the changes of water temperature were affected by other factors, including the location of the lakes, their morphometric parameters, wind speed, water transparency and water exchange time. [ABSTRACT FROM AUTHOR]