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>

Influence of Land Use Change on Hydrological Cycle: Application of SWAT to Su-Mi-Huai Area in Beijing, China

The human activities and urbanization process have changed the underlying surface of urban areas, which would affect the recharge of groundwater through rainfall infiltration and may further influence the groundwater environment. Accordingly, it is imperative to investigate the variation of hydrological cycle under the condition of underlying surface change. Based on the high-precision remote sensing data of 2000, 2005, 2010 and 2015, and Soil and Water Assessment Tool (SWAT) model, this work firstly studied the land use change and the corresponding changes in runoff generation mechanism and rainfall infiltration coefficient in Su-Mi-Huai area, Beijing, China. Meanwhile, SWAT-MODFLOW semi-loose coupling model was applied to analyze the water balance in the study area in typical hydrological years. The results showed that the area of the construction land (urban and rural residential land) increased by 1.04 times from 2000 to 2015, which is mainly attributed to the conversion of cultivated land to construction land in the plain area. This change caused the runoff in the area to increase by 7 × 106 m3, the runoff coefficient increased by 17.9%, and the precipitation infiltration coefficient was less than the empirical value determined by lithology. Compared with 2000, the average annual precipitation infiltration coefficient in 2018 decreased by 6.5%. Under the influence of urbanization process, the maximum reduction rate of precipitation infiltration recharge is up to 38%. The study investigated the response of surface runoff and precipitation infiltration recharge to land use change, which can provide helps for water resources managers to coordinate the relationship between land use change and rational water resources planning.

Temporal and Spatial Diversity of Renewable Groundwater Resources in the River Valley

Quantitative assessment of the amount of renewable resources allows their evaluation, valorization and protection in terms of the possibility of their environmental management under climate change conditions. The aim of the study was to determine the amount of renewable resources in the Middle Vistula valley, in the region of the Kampinos National Park, central Poland. The amount of renewable resources was calculated on a hydrodynamical model for three variants, as the average, the lowest and the highest infiltration recharge rate for a specified period of 1999–2013. The modelling research was conducted in a strongly differentiated hydrogeological valley unit, in which several geomorphological units could be delineated: the floodplain, over-flood terraces and the plain area. The hydrodynamic modelling results were verified by comparing the obtained data with both the amount of drainage in the valley zone and the underground streamflow. The assessment of renewable groundwater resources in three distinctive variants was the basis for calculating the groundwater footprints, defined as a quantitative assessment of the groundwater use in climate change conditions.

Abnormal groundwater flow system between two rivers: a numerical investigation

<p>Groundwater flow system has long been recognized as the local, intermediate and regional flow systems since Toth (1963). For groundwater flow in an unconfined aquifer between two parallel rivers (or ditches), as indicated by Hubbert (1940), there are two local flow systems contributing groundwater discharge to the two rivers from infiltration recharge. Surprisingly, this model has never been examined until Han et al. (2019) pointed out that something may be wrong: not only two flow systems exist. The problem was further investigated with a two-dimensional numerical model on MODFLOW for saturated groundwater flow below the arch-shape water table receiving a uniform infiltration recharge. Streamlines were obtained with MODPATH to identify the flow systems. We discovered that an abnormal groundwater flow system could emerge beneath the two local flow systems under some conditions, which forms a pass through flow from the high river to the low river. This pass-through flow system exists when the water level difference between the two rivers is sufficiently large and the infiltration recharge is sufficiently low. As a result, the base flow of the low river may be not only attributed to the captured infiltration recharge from the nearby local flow system but also partly originated from the high river. The ratio of the contribution from the pass-through flow system to the total groundwater discharge toward the low river could be higher than 20% and almost linearly increases with the water level difference between two rivers. More details of such an abnormal groundwater flow system were investigated as well.  </p>

Features of the balance structure formation of groundwater withdrawal and its effect on river flow at a subsoil water level drawdown

The balance structure of the pumpage sourses of riverside water-intakes, developing a subsoil aquifer or intermediate water that hydraulically interacts with it, can show the effect of the processes of water balance adjustment in the unsaturated zone to the accompanying subsoil water level drawdown. In this case, because of the shallow depth to subsoil water, its level drop due to water withdrawal causes a decrease in evapotranspiration and an increase in groundwater infiltration recharge. These processes have their effect on the balance structure of usable water resources as components of natural and involved resources and reduce the impact of groundwater pumping on river flow. Analysis of the operational data of the Sudogda waterintake in Vladimir oblast and geohydrological modeling were used to evaluate variations of the groundwater evaportanspiration losses and infiltration recharge and their role in the water balance structure of reserves of a field and in the impact of groundwater withdrawal on river flow.

Control of Contaminant Transport Caused by Open-Air Heavy Metal Slag in Zhehai, Southwest China

Slag heaps are formed by mining waste materials, and the improper treatment of leachate from such heaps can threaten nearby aquifers. The Zhehai slag heap in Yunnan Province, China, contains 2.7 million tons of zinc and cadmium slag, and is considered a heavy metal source threatening the local groundwater safety, however, the severity of contamination remains unknown. In this study, numerical modeling was used to predict the groundwater flow and contaminant transport in this area based on field data. The results show that the atmospheric precipitation infiltration recharge at the top of the heap is 81.8 m3/d, accounting for 93.76% of total infiltration. The south and east sides of the area are the main outflow channels for contaminants, accounting for 93.25% of the total discharge around the heap. To reduce aquifer contamination, an in situ system involving a “controlling the source, ‘breaking’ the path, and intercepting the flow” (CSBPIF) strategy is established. The results indicate that the system performs well because it not only decreases the flow velocity but also reduces the concentrations of contaminants adsorbed by clay media. Moreover, the equivalent bottom liner thicknesses of the clay layers were calculated to improve the applicability of the CSBPIF system. Compared with ex situ disposal, this scheme provides an economic and effective solution and can be used to prevent and control groundwater pollution in China.

Hydrogeological conditions of potable water supply the Kuznetsk Coal Basin, Russia

The article deals with hydrogeological conditions of the groundwater resources in the western part of the Kuznetsk depression, a coal and ore mining region. On the basis of a scheme of hydrogeological boundary conditions, a numerical geologic filtration model is developed for calculation of groundwater resources in the study area. The hydrologic budget of the numerical model is evaluated for assessment of infiltration recharge of groundwater resources.