Changes In Water Inflow Research Articles

Water-inrush mechanism from the head-on working face roof in a Jurassic coal seam in the Ordos Basin.

When Chinese coal mines are mining Carboniferous Permian coal seams, the mechanism of water inrush from the roof of the working face usually conforms to the "Upper Three Zones" or "Upper Four Zones" theory. The water inrush passageway is water-conducting fracture zone, and the water inrush position is located in the goaf. However, when mining Jurassic coal seams in Chinese coal mines, the location of water inrush often appears at the head-on working face, above the coal mining machine. Due to the support of the fully mechanized mining support, the roof rock layer cannot collapse and therefore cannot form water-conducting fracture zone. Therefore, the water inrush mechanism cannot be explained by the above two theories. This paper is guided by the Practical Mine Pressure Control Theory, and based on the explanation of the motion forms of bending (pulling) failure movement and shearing (cutting) failure movement, and combined with on-site examples, it is revealed that the passageways leading to from the head-on working face roof in a Jurassic coal seam in the Ordos Basin are splitting zones type, fracture line type and structural fracture type, respectively. Taking the changes in water inflow during the mining process of the 3301 and 3302 working faces in Zhujiamao Coal Mine as examples, this paper reveals the mechanism of water inrush from the head-on working face roof caused by splitting zones type, and proves the existence of this passageway through on-site 3D high-density electrical detection and tracing experiments. Taking two catastrophic water inrush accidents that occurred head-on in the 1309 working face of Guojiahe Coal Industry Co., Ltd. as examples, the water inrush mechanism of the fracture line type and the water inrush mechanism of the structural fracture type were respectively revealed. Based on mechanism of water inrush from head-on roof of working face and the analysis of the on-site water inrush process, a method for distinguishing the type of water inrush passageway from the front roof of the working face is proposed. The results indicate that the Jurassic coal seam mining in the Ordos Basin is prone to shearing (cutting) failure movement, resulting in the frequent formation of the three types of water inrush passageways mentioned above.

Adaptive ensemble models for medium-term forecasting of water inflow when planning electricity generation under climate change

Medium-term forecasting of water inflow is of great importance for small hydroelectric power plants operating in remote power supply areas and having a small reservoir. Improving the forecasting accuracy is aimed at solving the problem of determining the water reserve for the future generation of electricity at hydroelectric power plants, taking into account the regulation in the medium term. Medium-term regulation is necessary to amplify the load in the peak and semi-peak portions of the load curve. The solution to such problems is aggravated by the lack of sufficiently reliable information on water inflow and prospective power consumption, which is of a stochastic nature. In addition, the mid-term planning of electricity generation should consider the seasonality of changes in water inflow, which directly affects the reserves and the possibility of regulation. The paper considers the problem of constructing a model for medium-term forecasting of water inflow for planning electricity generation, taking into account climatic changes in isolated power systems. Taking into account the regularly increasing effect of climate change, the current study proposes using an approach based on machine learning methods, which are distinguished by a high degree of autonomy and automation of learning, that is, the ability to self-adapt. The results showed that the error (RMSE) of the model based on the ensemble of regression decision trees due to constant self-adaptation decreased from 4.5 m3/s to 4.0 m3/s and turned out to be lower than the error of a more complex multilayer recurrent neural network (4.9 m3/s). The research results are intended to improve forecasting reliability in the planning, management, and operation of isolated operating power systems.

Mechanical Properties of Sandstone Roof and Surrounding-Rock Control of Mining Roadways Subject to Reservoir Water Disturbance

Sandstone-roofed roadways are susceptible to deformation and failure caused by reservoir-water-induced disturbances, thereby compromising human safety. Using rock-mechanics testing techniques, numerical simulations, and engineering principles, this study investigates the strength, deformation, and pore-structure characteristics of sandstone roofs as well as means to support the surrounding rock structure. The results obtained in this study reveal that the residual strain is proportional to the pore-water pressure, which, in turn, causes a significant reduction in the elastic modulus during the unloading phase. Furthermore, an increase in the pore-water pressure causes the shear failure of specimens in compression. The delay between crack initiation and specimen-volume expansion decreases. Moreover, the specimen demonstrates increased deformation and failure responses to changes in the confining pressure, thereby resulting in accelerated conversion. Changes in water inflow can be correlated to crack initiation, propagation, and fracture. This water inflow gradually increases with an increase in the osmotic pressure. Correspondingly, the volumetric strain required for maximum water inflow undergoes a gradual decrease. The increased water inflow can be considered a precursor to specimen failure. In addition, fractures in the surrounding rock structures are mainly caused by joint dislocations. The increase in pore pressure promotes the development of dislocation fractures in the deep surrounding rocks. Subsequently, these fractures overlap with their open counterparts to form large fractures; this increases the roadway-roof subsidence and layer separation of the shallow surrounding rocks, thereby further increasing the fracture count. Lastly, the use of high-performance rock bolts, cable-bolt reinforcements, and W-shaped steel bands is expected to ensure the stability of rocks surrounding sandstone-roofed roadways subject to water-pressure disturbances.

Water exchange processes estimation in a temperate shallow lake based on water stable isotope analysis

ABSTRACT The estimation of lake hydrological characteristics such as evaporation/inflow ratios and water residence time becomes necessary for understanding cycling and potential retention of natural and anthropogenic substances into the lake. The aim of this work was to estimate the evaporation loss and the water residence time of a temperate shallow lake based on the water isotope mass balance approach. One representative freshwater temperate shallow lake from the Argentinian Pampa Plain was selected. Groundwater, lake and stream samples (N = 56) were collected for δ 2H-H2O and δ 18O-H2O determinations. Moreover, water level fluctuations of the lake and its inflow stream were recorded with data loggers. Both the δ 2H and δ 18O relationship and d-excess of lake water indicated evaporation. Water isotopes and daily stream flow data recorded in the inflow stream evidenced groundwater contribution to Los Padres Stream. Monthly evaporation as a fraction of inflow estimations of the lake water indicated that about 20–25 ± 12% lake water was lost through lake surface evaporation and revealed that hydrologic balances were regulated mainly by changes in water inflow rather than evaporation. A mean residence time of 1.11 ± 0.65 year was also calculated. This lake hydrological information is relevant for the region and crucial to improve water management plans.

Diatoms as biomarker in changes of the Lake Zapovednoye state (Evenkia, Russia)

As part of a multidisciplinary study aimed at paleoclimatic reconstruction in March 2015 and June 2018 cores of bottom sediments of Lake Zapovednoye (Evenkia, Russia) were obtained. Analysis of samples of bottom sediments by the diatoms composition - one of the main biomarkers or proxy of changes in a state of the lake, showed that, in addition to short-term changes, long-term changes in the species composition of diatoms at least twice occurred. It may be associated with changes in water inflow and level of Lake Zapovednoye. It is most likely these events could occur due to climate change.

Changes in Water Resources under Conditions of Climate Warming and Their Impact on Water Inflow to Russian Large Reservoirs

Changes are considered in the runoff regime of Russian rivers and in the water inflow to reservoirs as a result of the climate warming observed in the country since the second half of the 1970s. Based on the analysis of long–term observational data on water inflow to 41 large reservoirs with the volume of 10 x 106 m3, it is shown that considerable changes in its intraannual distribution have occurred in the recent decades. These changes are characterized, in particular, by the inflow increase during the cold season and by the runoff variability increasing in winter and summer–autumn seasons. The growth of the number of severe hydrological events, especially of flash floods induced by rainfalls, has been registered in the recent decades. Potential future changes in water inflow to reservoirs are considered in accordance with the scenarios of further climate warming. It is justified that rules of using water resources of reservoirs should be corrected taking into account the observed changes in the river water inflow regime.

Characteristics of current changes in water inflow into lake Baikal

We examine the changes in water inflow into Baikal that are taking place due to global warming that enhanced beginning in the 1970s as well as due to the different responses of discharges of separate rivers within the Baikal watershed basin to climate change.

Spatial and temporal variability of prairie lake hydrology as revealed using stable isotopes of hydrogen and oxygen

Evaporation and groundwater fluxes are thought to regulate hydrologic variability in lakes of the northern Great Plains, but little is known of how the relative importance of these processes may vary in time or space. To address this issue, we measured the isotopic composition of water (δ18O, δ2H) from 70 closed-basin lakes in southern Saskatchewan, Canada. All lakes occupied endorheic basins along a long gradient of salinity (0.2–115 g total dissolved solids L−1). Lakes exhibited synchronous seasonal changes in salinity (synchrony, S = 0.78) and δ18O (S = 0.84) during the dry summer of 2003 (~195 mm rain), whereas coherence was reduced to 0.56 and 0.22, respectively, during the wet summer of 2004 (~295 mm rain). However, despite evaporative enrichment of isotopic ratios during dry summers, hydrologic balances were regulated mainly by changes in water inflow (I) rather than evaporation (E) in both wet and dry years, with particularly strong influence of inflow (lowest E : I ratio) in dry southwestern regions. Analysis of isotopic composition also identified winter precipitation or groundwater as the most influential source of water to most lakes, despite only ~30% of annual precipitation being delivered during winter. Therefore, although seasonal variability in lake chemistry was influenced by evaporation during summer, long-term mean chemical characteristics of prairie lakes were regulated mainly by changes in winter precipitation or groundwater influx.

Changes of major ion concentrations in melting snow and terrestrial waters from northern Victoria Land, Antarctica

Concentrations of major ions (Cl−, NO3−, SO42−, Na+, K+, Mg2+, Ca2+) were measured in melting snow and water samples from streams and lakes in ice-free areas throughout northern Victoria Land. Most ions in snow and terrestrial water derive from the marine environment and their concentrations are extremely variable in space and time, especially in water systems without melting snow and ice. The distance from the sea, snow sublimation, changes in water inflow, evaporative concentrations, weathering and drainage processes in the catchment, nesting seabirds and aquatic microbiota are among factors which most influence ion composition variability. Comparisons with data from twelve years ago in the same lakes indicate that the warming trend detected at Terra Nova Bay station during this period did not affect the biogeochemistry of water systems. Waters from a lake which recently experienced a lowering of the water level showed a remarkable increase in SO42− concentrations. We hypothesized that the differential mobility of sulphate salts in the Antarctic soils, the biosynthesis of sulphur compounds in the lake, and the progressive decrease of the water volume are factors involved in the increase of SO42− concentrations.