GROUNDWATER RUNOFF IN THE PIVDENNYI BUH RIVER BASIN IN CONDITIONS OF GLOBAL WARMING

This paper analyses changes in the calculated values of the specific runoff of unconfined and confined groundwaters to the rivers Pivdennyi Buh (Khmilnyk town) and Zhar (a tributary of the Pivdennyi Buh; Vinnytsia and Khmelnytsky regions) by seasons and long-term stages, for a total of 38 years (1980-2017). Regularities of seasonal changes in groundwater runoff in areas with different relief and average long-term groundwater levels (0.5-1.5; 0.8-2.5 and 2.7-4.5 m) are revealed. These changes have been shown to be closely related to abnormal air temperature fluctuations. There are four stages of successive changes in the regime of groundwater and in the volume of their runoff to rivers: I. 1980-1989 (1990) — traditionally minimal winter and autumn underground runoff, moderate summer and predominant spring runoff, dominance of runoff from the area with high GWT; ІІ. 1990-1998 — growth and advantages of groundwater runoff from the area with low GWT, reduction to the long-term minimum of groundwater runoff in the area with high GWT (0.8-2.5 m); III. From 1999 to 2014 — the predominant dominance of winter runoff over spring, slow growth of groundwater runoff in a limited area of the catchment with levels of 0.8-2.5 m; high-amplitude fluctuations of runoff and GWT with the achievement of long-term maximums in the area with GWT = 2.5-4.0 m; IV. 2015-2019 — the most intense reduction of GWT, and in the upper reaches of small rivers — of underground runoff to rivers.There is a progressive decrease in the specific flow of groundwater to rivers, and consequently of their resources — primarily for the aquifers in the upper reaches of rivers with GWT 0.5-1.5 m with no pressure recharge. Aquifers of ground water fed by confined aquifers (mainly within floodplains and the first low terraces of rivers) in the studied area of the Ukrainian massif of fracture waters have greater stability of the level regime on the background of rising temperatures and decreasing precipitation (recorded by 2020) than shallow water (0.5-2.0 m) without signs of such recharge.

Formation features of river underground runoff under global warming conditions

<p>According to the results of processing long-term data series of hydrological and hydrogeological monitoring in the upper part of the Southern Bug river basin, it has been found that meteorological or climatic changes affect both terrestrial hydrosphere and shallow groundwater aquifer (level = 0.5…7.0 m). There are two stages of different effects of temperature changes on the groundwater regime: the first stage (1974-1998) had a positive impact, with an increased infiltration recharge and large-scale flooding, while the second stage (1999-2020) is characterized by increasing drought. The average annual infiltration recharge of groundwater on the first terrace above the flood-plain at the first stage has reached 191.6 mm that is quite high for this climatic zone, while at the second stage – 115.0 mm. The highest groundwater runoff to the river was recorded in 1987-1989 (the first terrace above the flood-plain), 1996-1998, 2005, and 2014 (from the left-bank catchment). By seasonal distribution, the spring runoff mostly prevailed in 1981-1986; starting from 1996-1999 (in different areas) – summer runoff, especially in years with maximum underground runoff; the winter runoff to the river slightly prevailed in certain years (1994, 1998, 2000, 2008, 2015).</p><p>With the transition from a low-water cycle of years to a water-rich cycle (and vice versa), the dominant cyclicity in the regime of groundwater and surface water changes from 5-6 years to 7-8 years.</p><p>1974-1975 and 1987-1989 had certain temperature limits that caused significant changes in the groundwater level regime: firstly, at long-term annual average depths of 1.5-1.8 m under the surface, and later at depths of 3.0-4.4 m having led to the transition and consolidation of levels at higher grades. At the second stage, the trends of precipitation, groundwater and surface runoff change significantly (surface runoff decreases most rapidly, while the intensity of groundwater runoff has slowed down), but the temperature rises with almost the same intensity. The dependence of the total river runoff on the underground increases.</p><p>In the long-term plan (40 years), groundwater and river runoffs change in opposite directions, as the regime-forming factors (temperature and precipitation) have different effects on them: rising temperatures at the first stage have led to increased groundwater runoff; at the same time, the intensity of the decrease in river runoff under the influence of temperature as well as the decrease in precipitation at the second stage increase. The difference in the rate of reactions of groundwater and surface water levels to precipitation still provides an increase in groundwater runoff by increasing the flow gradient to the river. With decreasing rainfall, this scenario will certainly lead to the depletion of groundwater reserves.</p>

Hydrological Regime of the River When Changing the Landscape Structure of the Catchment Area (by the Example of the River Goloustnaya)

The main features of the hydrological regime of the river are strategic regional characteristics. At the same time, a significant effect on surface and groundwater runoff, evaporation and transpiration determines the landscape of the transformation of atmospheric precipitation entering the drainage area, surface and groundwater runoff. The existing basin landscape structure has hydrological properties that change when structural components are disturbed. The article examines the relationship between the intra-annual regime of the river and changes in the landscape structure of the catchment area over ten years. An estimate of the size of landscape transformations is proposed based on data on global changes in forest cover in the world in the 21st century – high-resolution global maps of changes in forest cover in the 21st century. The analysis of the dynamics of characteristics of runoff, precipitation and area landscapes is carried out. The dependence of the hydrological regime of the river on the structural transformations of the drainage landscape was revealed for the phase of the upper rainfall runoff. An increase in water discharge in the river against the background of total precipitation was noted, which indicates a change in the landscape-hydrological properties of the catchment. As a result of the reduction in the areas of dark coniferous landscapes, which have significant runoff- regulating functions of the territory of the hydrological regime, the values and amplitudes of the rises of rain floods increase. Investigations of landscape-hydrological transformations of watersheds is an important direction in optimizing the use of natural resources in watersheds and minimizing the negative impact of natural waters.

SPATIAL-TEMPORARY REGULARITIES OF THE SURFACE AND UNDERGROUND FLOWS OF THE RIVERS OF THE GREAT CAUCASUS

The analysis of the statistical structure of the ranges is carried out, the degree of synchronism of fluctuations in runoff characteristics is estimated, and linear trends are identified. The annual values of groundwater runoff have been determined as the arithmetic average of the monthly average minimum winter and summer-autumn water discharges, the surface runoff being calculated as the difference between the annual and groundwater runoff. The stationarity of most of the considered ranges proves to be violated by dispersion or average value. For underground runoff, the number of such ranges according to the Fisher and student criteria is 9 and 12, and for surface runoff, 7 and 9, respectively. For 15 rows of underground runoff and 9 rows of surface runoff, autocorrelation coefficients are statistically significant at a 5 % level of significance. Differential integral curves have been drawn according to the data of each river, the temporal indicators of various phases of water content being determined from them. For the long-term, fluctuations of the underground flow of all the studied rivers are characterized by the presence of a prolonged low-water phase. To quantify the degree of synchronism of long-term fluctuations in the underground flow of rivers, the pair correlation coefficients between all the analyzed series have been calculated. In the long-term fluctuations of both the underground and surface runoff of the rivers of the Greater Caucasus, asynchrony has not been detected. Over the long-term observation period, the underground runoff of the vast majority of rivers is shown to be increasing. For ranges of surface runoff, multidirectional trends have been found. Most of the linear trends in groundwater flow and half of the trends in surface runoff are statistically significant. The significance of linear trends has been estimated by the values of the pair correlation coefficient and its standard error. The data on the runoff of 17 hydrological observation points covering 1934—2017 period have been used

Method for Identifying and Estimating Karst Groundwater Runoff Components Based on the Frequency Distributions of Conductivity and Discharge

Identification and estimation of groundwater runoff components in karst groundwater systems to improve understanding of karst water circulation and water-rock interactions is essential for water resources assessment and development. A Gaussian mixture model is presented for identifying and estimating karst groundwater runoff components based on the frequency distributions of conductivity and discharge. Successful application of this method in the Heilongquan karst spring in South China showed that groundwater runoff components can be divided into 6–8 grades, corresponding to the grades of groundwater in karst fissures. The conductivity and discharge thresholds dividing fast and slow flow were determined to be approximately 300 μS cm−1 and 0.3 m3 s−1, respectively, with fast flow exhibiting lower conductivity and larger discharge. On an annual basis, fast flow occurred 9% of the time and accounted for 35% of total water volume. The results of the method compared favorably to that of hydrograph recession analysis. Estimation of groundwater runoff components based on frequency distributions of conductivity and discharge provides a novel alternative method for the quantitative evaluation of karst water resources.

The Groundwater Runoff Formation Conditions in the Rivers of the Verkhnemstinskiy Basin

Assessment of the physical/geographical, geological, and water/economic factors on the Verkhnemstinskiy basin rivers’ groundwater runoff is presented. It has been shown that groundwater runoff to rivers high parameters are determined by favorable lithologic and climatic conditions, as well as a big number of lakes in the region. The Vyshnevolotsk hydraulic engineering system big water reservoirs considerably influence the rivers’ minimal low water and groundwater runoff. Earlier State Hydrological Institute and other research organizations performed assessment of the groundwater input to the rivers on this territory in 1970–1980. However, these works had not always stressed the connection between the calculated groundwater runoff parameters with local natural conditions. At the same time, Rosgidromet, State Hydrological Institute, and other institutions have accumulated considerable volume of data concerning this region rivers minimal low water and groundwater runoff. This paper systematizes these important hydrological characteristics in respect of the Verkhnemstinskiy basin and defines parameters of groundwater input to the rivers, lakes and reservoirs of this region.

Groundwater renewable resources in karst areas, the case of the Kleśnica River basin (Sudety Mountains, Poland)

The karst-fractured medium constitutes a considerable groundwater capacity, as shown on the example of the Kleśnica River basin. The paleozoic crystalline limestones in the research area are good collectors of the groundwater. The Kleśnica River basin, one of the largest crystalline limestone lens, is situated in the Sudety Mountains. Groundwater renewable resources were distinguished with the use of hydrological methods, on the basis of hydrometric measurements of the flow discharge of the Kleśnica River during the low-flow period (2009–2010). The mean module of the groundwater runoff equals 20.79 dm3/s*km2, and includes the study of the river catchments areas with extremely high groundwater runoff. The groundwater renewable resources in the Kleśnica River basin are almost twice higher than in the neighbouring river basins (the Kamienica and Morawka River basins), in which there are no significant outcrops of carbonate rocks. These considerable renewable resources also provide a high runoff in the spring, 7.98 dm3/s*km2. The high values of the runoffs indicate, that the groundwater is coming from the regional circulation system and, on a smaller scale, from the local system. The groundwater from both systems flows into the fractured system through the karst of carbonate massif rocks and their weathering fringes.