The monograph represents the theoretically summarization of the experimental results obtained during 35-year studies of artificial radionuclides hydrogeomigration in geological and conjugated environment. Modern problems of radioecological monitoring are actualized. The processes of groundwater self-cleaning from radionuclides have been investigated and parameterized. A number of radio-ecological factors of artificial radionuclides biogeomigration in sub aquatic landscapes within the Ukrainian Polissia (Woodlands) have been identified, which determine the barrier functions of forestry-marsh biogeocenoses. Methodological and methodical approaches to the analysis of long-term monitoring observations within the catchment areas contaminated with radionuclides are considered. The main task of such studies is to establish the degree of barrier stability of the landscape complex of the catchment for water intake. The level of generalizations, local (close to the object), regional or global is substantiated by studies of the appropriate level, which should be started with the establishment of the share of secondary contamination of surface waters with radionuclides that is related to the implementation of the balance method. The methods of scientific analysis also include a variety of statistical methods aimed at identifying landscape and geochemical factors responsible for the deposition, migration, and assimilation of radionuclides within watersheds. The described factor selection procedure is the basis for predicting the concentrations and aqueous removal of radionuclides. On this basis, a forecast of radionuclide water migration for local and regional levels has been developed. Examples of the analysis of efficiency of the executed and substantiation of possible water protection and fire-prevention measures in the Chernobyl exclusion zone are presented. The monograph is designed for experts in the fields of radiogeochemistry, biogeochemistry, hydrology and hydrogeology, radioecology, agro-ecology, technogenic-ecological safety and security, conducting monitoring studies, as well as for students of natural specialties of higher education institutions.

The data of observations since 1951 in the upper part of the Southern Bug River basin in the west of Ukraine are analyzed. The results indicate that the climate change occurring on Earth disrupts the regular cyclicity of groundwater flow indicators. The identified 7–8-year groundwater level and flow to the river cyclicity correlates well with the air temperature, precipitation and river runoff cyclicity. The noted groundwater cyclicity appears with some delay after the establishment of the 8-year air temperature cyclicity observed since 1969. The manifestation of a 7–8-year cycle depends on the groundwater table (GWT) depth. For shallow groundwater (1.0–2.5 m), such rhythms have been observed since 1975, and for deeper levels, since 1989, which is recognized as the year of the beginning of the climate changes. Moreover, 7–8-year rhythms in the fluctuation of groundwater parameters are characteristic of mainly high-water periods of their multiyear regime, and during the low-flow phase is significantly weakened. During 2011–2014, the groundwater levels abnormally decreased and the 8-year cycles were replaced with 5-year ones. The influence of air temperature on the groundwater regime exceeds the role of other factors. Wavelet analysis was used as the main method of periodicity observation. Gaussian and Morlet wavelets provide the visualization of pronounced periodicities of data. Using multiple correlation analysis, it was confirmed that temperature has become the dominant impact factor on the groundwater (GWT 1.5–4.0 m) regime in recent decades.

The article considers the relevance of the application of a set of terrestrial hydrological, radioecological and modern remote sensing methods in the process of monitoring studies of areas that are difficult to access, waterlogged, largely radionuclide contaminated. The example of the Ukrainian part of the left-bank Pripyat drainage system within the Chornobyl Exclusion Zone shows that remotely obtained data together with the materials integrated into the geographic information systems of the terrestrial measurements provide the adequate monitoring information on the spatio-temporal changes in the hydrological and radioecological situation in general. Among the research methods, the simulation, the methods of hydrometric, balancing, remote sensing studies of water bodies were most used. The main purpose of the research is to perform the retrospective and current analyses of the hydrological situation based on archival and recent satellite images, assess the effectiveness of the water protection complex on the left bank of the Pripyat River, especially after the introduction of hydrotechnical measures to improve its radioecological status. In the research process the LANDSAT, SPOT, IRS, WorldView images were used. In particular, a significant sensitivity of the "surface water – dry land" system to the changes in the environment of this area was established and the mapping of objects of open water surface was performed as well as its spatial and temporal variability was followed. When comparing the results of calculations of the radionuclides carry-over by water (in particular, 90Sr) before and after the implementation of appropriate measures at the water protection complex the notable negative consequences of its implementation and operation during a period from 1986 to 2001 were revealed. It was found that the diverted one-time 90Sr carry-over due to the construction of a "new" left-bank dam (according to the 1999 flood scenario) is "compensated" by 40% through the increase of its carry-over prolonged in time as a result of operation of the polder pumping station (PPS) and the inundation of the contaminated areas, which is caused by the complicated conditions for the discharge of surface and underground runoff caused by the "new" and "old" dams. The ecological advisability and validity of hydraulic measures (clearing of canals, reconstruction of culverts) and the recommended form of the operational complex (without the use of PPS, with natural filtration discharge of the body of the "new" sand dam in the Pripyat River) are confirmed by the results of thematic interpretation of the multiband images. Thus, within the complex, minor flooding and waterlogging of the inter-dam section, as well as areas to the north-east from the "old" dam are established. Prospects for the further research of various hydrological processes and radioecological situation on the left bank of the Pripyat River are seen in the use of high resolution remote surveys, which would be performed over the short periods of time. The informative result in good quality can be obtained on the basis of the use of unmanned aerial vehicles technology.

In the case of absence of reliable information on fluctuations of levels and hydraulic parameters of aquifers within a large catchment, the method of river hydrograph decomposition can be used to assess groundwater component and other constituents of river water recharge. The difficulties and shortcomings of this method, which relies on specific schematizations and assumptions, are analysed and discussed. We propose to take into account the results of calculations of lateral groundwater inflow to the river accomplished using the numerical method based on observations at representative balance sites in order to improve the accuracy of the method of decomposition of the river hydrograph. A proper schematization should also be justified for river catchment (or its part), which describes the interaction of surface water, shallow groundwater, and artesian (deep) interlayer waters, which provides rationale for defining or neglecting groundwater inflow to river during the flood periods. The most disputable issue remains the allocation of the phase of “reverse water inflow to river banks” during flood periods. The groundwater level rise at the beginning of the flood results from the infiltration recharge to the aquifer and from inflow of water from the river. The contribution of inflow to river bank to groundwater level rise is dependent from the distance from the river to the observation well. To establish hydraulic head gradient from the river towards the adjacent groundwater aquifer at flood peak, at least two observation wells are needed, one of which should be located 3–4 m from the river water edge on the elevated part of the bank which is not flooded, and the other should be located 50–70 m from the bank towards the watershed. It is proposed that the phase of maximum groundwater inflow to the river should be adjusted based on the dates of the beginning and ending of the groundwater level decrease during the recession of the river flow during the flood period. The combined application of the described above methods showed that the use of only hydrograph decomposition method underestimates the share of groundwater recharge to the river by 2–5%. Based on the analysis of the Pivdennyi Buh River hydrographs during the 1980–2020 period, general tendencies of changes in the shallow groundwater and deep subsurface recharge of the Pivdennyi Buh River in its upper basin (upstream of the city of Khmilnyk) have been established: deep subsurface recharge prevailed over the shallow groundwater component (33.4 compared to 25.0% of the total). At the same time, the total subsurface runoff constituted on average 58%. Для оцінки підземної та інших складових живлення річок, за відсутності достовірної інформації про коливання рівнів та фільтраційні параметри водоносних горизонтів на великому водозборі, використовують метод розчленування гідрографа річки. В статті проаналізовано суперечності та недоліки цього методу, який спирається на певні схеми та припущення. Для підвищення його точності ми пропонуємо враховувати результати розрахунків бічного припливу ґрунтових вод до річки, виконані чисельним методом за даними спостережень за рівнем ґрунтових вод на репрезентативних балансових ділянках. Слід також обґрунтовувати найбільш поширену для водозбору (або його частини) схему взаємодії поверхневих, ґрунтових і напірних міжпластових вод, яка дає підстави для виділення грунтового стоку або нехтування ним на час повені. Найбільш дискусійним залишається питання щодо виділення фази «зворотного живлення» ґрунтових вод під час водопілля. Підйом рівня ґрунтових вод на початку водопілля варто розглядати як функцію інфільтраційного живлення та підпору від річки. Внесок підпору регулюється відстанню від річки до спостережної свердловини. Для підтвердження підпору ґрунтових вод на піку повені слід мати щонайменше дві свердловини, одна з яких розміщується в 3–4 м від урізу води на підвищеній частині берега, що не затоплюється, а друга – на відстані 50–70 м від неї в бік вододілу. На спаді повені, з початком зниження рівня води в річці, насамперед спрацьовується купол підпору грунтових вод. Фазу наростаючого припливу ґрунтових вод до річки, яка виділяється на гідрографі на етапі зменшення повеневих витрат, пропонується коригувати за датами початку та закінчення зниження рівня грунтових вод. Комплексування методів показало, що застосування лише методу розчленування гідрографа занижує частку живлення річки...

Given that the hydrodynamics of internal and external water exchange in reservoirs creates fundamentally different living conditions for hydrobionts and significantly affects water quality, the task of separating the volumes of internal and external water exchange arises. The aim of the study is to obtain estimates of the magnitude and variability of internal and external water exchange in the Kyiv reservoir depending on the reservoir level. The research method is full-scale modeling, which consists in observing the dispersion in space of a certain passive conservative admixture (tracer) artificially introduced into the flow. As a tracer, we propose 90Sr, which by its properties almost meets the requirements for a tracer substance. The data of hydrological and toxicological monitoring in 1990-1991, 1993-1994 and 1998-1999 were used. Based on the data on 90Sr inputs to the upper reaches of the Kyiv Reservoir in 1991, 1994, and 1999, which had the character of sharp spikes, and the data on 90Sr concentrations at the outlet of the Kyiv Reservoir, the values of transport time and volumes corresponding to the time of contamination transport to the outlet of the reservoir were established. Guided by the transportation time and data on water consumption in the reservoir, calculated by the balance model, the values of the volumes of internal and external water exchange, as well as the parts that these volumes makeup of the total volume of the reservoir, were obtained. An interpolation of the dependence of the internal water exchange volume on the level of the Kyiv reservoir was constructed. The results obtained are in good agreement with some results obtained with the hydrodynamic mathematical model using the full-flow method by another group of researchers. The dependence of the volumes of internal and external water exchange of reservoirs on the reservoir level can be used to determine the time of pollution transportation along the reservoir, for environmental assessments and forecasts related to the study of water quality conditions.