Low Water Level Research Articles

Electrolyte Solvation Structure Regulation Promotes Aluminum–Air Batteries to Approach Theoretical Discharge Capacity

Aluminum–air batteries (AABs) feature high energy density and no limitations for charging facilities but suffer from severe self-corrosion reactions. Suppressing the side reaction between water and aluminum is the fundamental strategy to boost AAB performance. Herein, we first disclose that addition of sodium formate (HCOONa) can largely remold the solvation structure of the classic NaOH electrolyte and greatly reduce the amount of free water, thus constructing AABs close to their theoretical capacity. Ab initio molecular dynamics simulations show that multiple Na+ and H2O form hydrated Na+ ion clusters [Nam(OH2)7m]m+ in the HCOONa–NaOH electrolyte. Meanwhile, HCOO– enters the first solvation layer of Na+ and forms a “stable triangle” with Na+ and H2O. The coordination network formed by Na+, H2O, and HCOO– results in a very low level of free water. Moreover, HCOO– further forms a self-assembled passivation layer on the Al surface. As such, the self-corrosion rate of Al in the HCOONa-based electrolyte is drastically reduced. More encouragingly, the ultrahigh capacity (2767 mAh g–1) delivered by AABs using the hybrid electrolyte reaches 92.9% of its theoretical value, concurrently achieving a high energy density of 3702 Wh kg–1. This work paves the way for constructing durable AABs through an electrolyte regulation strategy.

Influence of sediment composition on morphology and internal structure of mixed siliciclastic–bioclastic coastal barriers: Contribution of flume experiments

ABSTRACTCoastal barriers are dynamic systems, the morphology and architecture of which are controlled by local hydrodynamics, sea‐level fluctuations at different timescales, geological heritage and sediment composition. Coastal barriers may be composed of siliciclastic sediments, bioclastic sediments, or a mixture of both. Mixed siliciclastic–bioclastic sediments (as common as ‘pure’ sediments) are still little represented in the literature. Changes in sediment composition could affect sedimentary processes which are involved in the construction and stability of coastal barriers due to a different hydrodynamic behaviour between bioclastic and siliciclastic particles. In this study, wave‐flume experiments were used to investigate the role of sediment compositional mixing on the morphology and architecture of coastal barriers. Three different siliciclastic/bioclastic mixtures were exposed to regular wave forcing, together with mean water level fluctuations to create regressive and transgressive depositional units. Compositional mixtures responded similarly in first‐order to mean water‐level fluctuations, with the formation of a bar at low water level. Its subsequent on‐shore migration and reworking as berm deposits during rising water level stages, and with the formation of washover deposits during high water level stages. In detail, the increasing content of bioclastic sediment increased the beachface slope and reduced the length of washover deposits. The faster aggradation of washover sheets with bioclastic‐rich mixtures accelerated the barrier recovery after a submersion and breaching event. A strong segregation between the siliciclastic and the bioclastic grains was observed in the different depositional units, which is attributed both to the coarse size (grain‐size control) and to the flat‐shape (compositional control) of the bioclastic particles.

Assessment of the Hydrological Conditions of Carps Spawning Grounds in the Sylhet Haor Basins, and the Halda River System, Bangladesh

The Halda River and Haor basins are considered unique breeding habitats for carps in Bangladesh. The purpose of the study was to evaluate the natural spawning environment of carp species, with an emphasis on the hydrological conditions of the Halda River, the Surma River, and Tanguar Haor. This study, which covers the years 2021 and 2022, considered two spawning seasons. The results revealed that temperature, total dissolved solids (TDS), salinity, turbidity, conductivity, and pH were significantly different in the Halda River to the Surma River and Tanguar Haor. However, sudden rainfall and upstream runoff in 2021 were deemed as major factors causing an increment in TDS and electrical conductivity. The water pollution index was excellent in the Surma River and Tanguar Haor, and good in the Halda River. The study reported moderately reduced IMC fry production in 2021 because of inconsistent turbidity, high conductivity, and increased salinity which interrupted the ideal spawning habitat. However, in 2022, the spawning environment was favorable in the Halda River, while the Surma River and Tanguar Haor were considered to be comparatively favorable in both years. Differences were also found in the climatic and meteorological conditions, which revealed uneven rainfall, higher temperatures, decreasing water discharge, and low water levels. The meteorological data also revealed that the overall rainfall showed a decreasing trend for all sites in the last 20 years causing an interrupted water discharge. It was discovered that the amount of carp spawn obtained in the Halda River was greater than that obtained in the Surma River and Tanguar Haor. In terms of hydrological conditions and spawning performance, the Surma River and Tanguar Haor were reported to have significant differences, which may be due to their geographical location.

Response of redox zoning and microbial community structure in riverbed sediments to the riverbed scouring during bank filtration

Riverbed sediments are an important zone and interface for the interaction of surface water and groundwater; hence, biochemical processes in the riverbed sediments are critical to maintain the ecology of the system and water quality. Riverbed sediment scouring can substantially alter the hydrodynamic conditions of river water infiltration and redox conditions at the surface–groundwater interface, which in turn affects the biochemical processes. Currently, in-depth understanding of the distribution characteristics of the microbial community structure in riverbed sediments, especially their response to riverbed scouring, is lacking. This study revealed the temporal and spatial changes in redox indicators in the Liaohe riverbed sediment and discussed the response of the microbial community to the influence of riverbed scouring. The results showed that during the investigation period (September to November 2020), the riverbed sediments in the river reach were generally in a state of scouring in the low water stage, and the scour depth was 4–9 cm. The redox zone in the nearshore area moved up by 5.5–23 cm, and moved down by 0.1–10 cm in the intermediate transition area and the center of riverbed, and the maximum overlapping depth of the redox zone could reach 50 cm. The relative abundance of dominant bacteria species had a good correlation with the intensity of geochemical reactions, decreasing in low-water levels close to the center of the riverbed, which further indicated the weakening of the reduction rate. Influenced by riverbed scouring, the species of denitrifying bacteria in the surface layer increased, multiple dominant bacteria of iron, manganese and sulfate often coexist in deep riverbed sediments, and were slightly different in the low water level. The results provide a better understanding of the chemical composition of the pore water in the riverbed sediments, which are of great significance for maintaining the ecological safety of river water.

Inability of yellow‐bellied toad to accelerate metamorphosis in desiccation conditions

AbstractMany amphibian species inhabit temporary aquatic habitats for reproduction to maximize larval growth under favorable conditions, but accelerate developmental rate to rapidly undergo metamorphosis under stress conditions when high desiccation risk exists. Desiccation affects different aspects of amphibian biology such as developmental rate, body size and mass, and growth rate. We studied the responses of yellow‐bellied toad (Bombina variegata) to different water levels (constant high, decreasing water level, and constant low water level) in the laboratory using individuals collected from natural ponds. To assess the effects of experimental pond drying, we investigated the effects on life‐history and morphological traits at metamorphosis as well as carry‐over effects on post‐metamorphic traits and locomotor performances. We found that B. variegata cannot accelerate developmental rate in response to pond drying. The metamorphs from decreasing and constant low water levels had similar size, mass, growth rate and body condition indices at metamorphosis, and all these traits were lower than in the constant high water level treatment. These changes in life‐history traits at metamorphosis did not affect tail shape although they had carry‐over effects on life‐history and morphological traits after metamorphosis. Post‐metamorphic individuals reared in desiccation treatments had similar but smaller lengths of femur and tibiofibula, but these changes did not have negative consequences on jumping performances. We show that responsiveness to pond drying of B. variegata is probably associated with maximum growth rate in favorable conditions and inability to increase growth rate as well as developmental rate in desiccation conditions. This resulted in prolonged developmental time to reach the minimum size and mass for metamorphosis.

Reconstructing the provenance of the hominin fossils from Trinil (Java, Indonesia) through an integrated analysis of the historical and recent excavations

In the early 1890s at Trinil, Eugène Dubois found a hominin skullcap (Trinil 2) and femur (Trinil 3, Femur I), situated at the same level ca. 10–15 m apart. He interpreted them as representing one species, Pithecanthropus erectus (now Homo erectus) which he inferred to be a transitional form between apes and humans. Ever since, this interpretation has been questioned—as the skullcap looked archaic and the femur surprisingly modern. From the 1950s onward, chemical and morphological analyses rekindled the debate. Concurrently, (bio)stratigraphic arguments gained importance, raising the stakes by extrapolating the consequences of potential mixing of hominin remains to the homogeneity of the complete Trinil fossil assemblage. However, conclusive evidence on the provenance and age of the hominin fossils remains absent. New Trinil fieldwork yielded unmanned aerial vehicle imagery, digital elevation models, and stratigraphic observations that have been integrated here with an analysis of the historical excavation documentation. Using a geographic information system and sightline analysis, the position of the historical excavation pits and the hominin fossils therein were reconstructed, and the historical stratigraphy was connected to that of new sections and test pits. This study documents five strata situated at low water level at the excavation site. Cutting into a lahar breccia are two similarly oriented, but asynchronous pre-terrace fluvial channels whose highly fossiliferous infills are identified as the primary targets of the historical excavations (Bone-Bearing Channel 1, 830–773 ka; Bone-Bearing Channel 2, 560–380 ka), providing evidence for a mixed faunal assemblage and yielding most of the hominin fossils. These channels were incised by younger terrace-related fluvial channels (terminal Middle or Late Pleistocene) that directly intersect the historical excavations and the reconstructed discovery location of Femur I, thereby providing an explanation for the relatively modern morphology of this ‘bone of contention’. The paleoanthropological implications are discussed in light of the current framework of human evolution in Southeast Asia.

Effect of rural domestic sewage regeneration irrigation on paddy soil properties and water and nitrogen utilization in southern China

AbstractRural domestic reclaimed water (RDRW) for agricultural irrigation is an effective way to alleviate the contradiction between the supply and demand of water. In this research, four kinds of irrigation water sources (primary and secondary treated water [R1 and R2], purified water [R3] and river water [CK]) and three kinds of water level regulations (low, medium and high water level control [W1, W2 and W3]) were set to study the impact of RDRW irrigation and its reuse on the properties of paddy soil, water and nitrogen utilization and yield of rice through a combination of field experiments and laboratory and numerical analysis methods. The results showed that compared with river water (CK) irrigation, pH (0–40 cm), electrical conductivity (EC) and organic matter (OM) content (60–80 cm) increased, and ammonium‐nitrogen (NH4+‐N) (0–20 cm) and nitrate‐nitrogen (NO3−‐N) (40–60 cm) content accumulated under RDRW irrigation. Under high water level regulation (W3), NH4+‐N and NO3−‐N content increased, showing the opposite changing trend compared with W1 and W2 regulations. With RDRW irrigation, water and nitrogen use efficiency and rice yield were significantly increased. Under RDRW irrigation, irrigation water use efficiency (IWUE), nitrogen use efficiency (NUE) and rice yield were increased by 48%–70%, 10%–22% and 5%–13%, respectively, compared with CK irrigation. In addition, path analysis established by structural equation modelling (SEM) showed that the irrigation water amount (IWA) had a significant positive impact on NUE and NH4+‐N but had a significant negative impact on IWUE and EC. NUE, IWUE, NO3−‐N and EC had a significant positive impact on yield. The path of IWA= > IWUE= > yield showed a complete mediation effect, the path of IWA= > EC= > yield and NUE= > EC= > yield both showed a partial mediation effect, and the effect size was 27.9% and 25.0%, respectively.

Environmental extremes affect productivity and habitus of common reed in intermittent wetland

This article describes the effect of extreme water level events and extreme temperatures on the primary productivity and habitus of the common reed (Phragmites australis) growing in lake and riparian habitats at intermittent Lake Cerknica between 2007 and 2021. At each sampling site, the above-ground biomass, leaf biomass and shoot density per m2, the number of internodes and leaves per plant, average shoot height, shoot basal diameter and the ratio of flowering plants per total plant number were determined. Stand and plant properties varied significantly between the locations, with exception of the basal diameter, that varied less. Biomass per area and per plant showed the trend of decrease across years, but the reed density remained at the same level. Redundancy analysis of the relationships between environmental parameters and productivity and habitus parameters revealed the importance for the lake stand of high-water level parameters in the 4th quarter of the previous year, while the 1st quarter of the current year was important for the riparian stand. High water level variables explained 60% of variance of productivity parameters of the lake stand and 21% of those of the riparian stand. For low water level parameters, the explained variance was 51 and 24%, respectively. In the case of habitus parameters, variances explained by high water level parameters were 66% for lake stand and 34% for riparian stand and of low water level parameters, the corresponding variances were 45% for lake stand and 59% for riparian stand. Temperature extremes can explain the lower variance. The interrelation between wetland hydrological extremes and reed stand/plant properties that was obtained suggests that an ecohydrological approach may provide a basis for successful management of reed-colonised wetlands.

Effects of arbuscular mycorrhizal fungi on plant growth and herbivore infestation depend on availability of soil water and nutrients.

Fitness of plants is affected by their symbiotic interactions with arbuscular mycorrhizal fungi (AMF), and such effects are highly dependent on the environmental context. In the current study, we inoculated the nursery shrub species Artemisia ordosica with AMF species Funneliformis mosseae under contrasting levels of soil water and nutrients (diammonium phosphate fertilization), to assess their effects on plant growth, physiology and natural infestation by herbivores. Overall, plant biomass was synergistically enhanced by increasing soil water and soil nutrient levels. However, plant height was surprisingly repressed by AMF inoculation, but only under low water conditions. Similarly, plant biomass was also reduced by AMF but only under low water and nutrient conditions. Furthermore, AMF significantly reduced leaf phosphorus levels, that were strongly enhanced under high nutrient conditions, but had only minor effects on leaf chlorophyll and proline levels. Under low water and nutrient conditions, specific root length was enhanced, but average root diameter was decreased by AMF inoculation. The negative effects of AMF on plant growth at low water and nutrient levels may indicate that under these conditions AMF inoculation does not strongly contribute to nutrient and water acquisition. On the contrary, the AMF might have suppressed the direct pathway of water and nutrient absorption by the plant roots themselves despite low levels of mycorrhizal colonization. AMF inoculation reduced the abundance of the foliar herbivore Chrysolina aeruginosa on plants that had been grown on the low nutrient soil, but not on high nutrient soil. Fertilization enhanced the abundance of this herbivore but only in plants that had received the high water treatment. The lower abundance of the herbivore on AMF plants could be related to their decreased leaf P content. In conclusion, our results indicate that AMF negatively affect the growth of Artemisia ordosica but makes them less attractive to a dominant herbivore. Our study highlights that plant responses to AMF depend not only on the environmental context, but that the direction of the responses can differ for different components of plant performance (growth vs. defense).

Performance Comparison of Straight, Curved, and Tilted Blades of Pico Scaled Vortex Turbine

In the 26th Conference of the Parties (COP26), United Nations Framework Convention is committed to suppressing the acceleration of climate change due to carbon by applying energy from fossil fuels to New Renewable Energy (NRE). Indonesia targets that in 2060 the coal phase-out will be replaced by renewable energy 2056. As a tropical country with many rivers and many lakes, Indonesia has a water energy potential of 75,000 MW. In some remote areas, the need for electrical power is pico scaled (< 5kW). The vortex turbine was chosen to be suitable for river flow with low water levels, low maintenance and construction costs, as well as being environmentally friendly for the underwater ecosystem. This study aims to compare the performance of the vortex to the differences in the shape of the pico scale blade. This study was carried out with variations in the shape of the straight, tilted, and curved blades. Based on the results of all vortex turbine studies, it can be ascertained that the best blade shape obtained numerically is an inclined blade with a hydraulic efficiency of 36%.

One Ranney Well Can Make a Difference: The Impacts of a Radial Collector Well on Groundwater Level and Quality in the Cedar River Alluvial Aquifer

AbstractThe City of Cedar Rapids, Iowa, depends on groundwater from the Cedar River alluvial aquifer for residential and industrial use. In 2020, the city completed an additional radial collector well, or Ranney well, and was concerned that pumping from the well at high rates may lower water level elevations in the aquifer, reduce yields from nearby production wells, and change the quality of produced water. During an operational test of the well's pumps, the U.S. Geological Survey and the city collected water level and water quality data to evaluate the effects of increased pumping rates on the aquifer and nearby production wells. Results indicated that a high rate of pumping from the new well caused sustained declines in water levels near the well and other nearby production wells, and, if maintained, the aquifer water level in the vicinity would continue to decline to levels observed during the 2012 drought. Aquifer specific conductance and temperature were altered and matched trends and values of the river, and river‐to‐well travel time was shortened from 7‐17 days to about 3 days. Results may also provide insights to other municipal water resource managers when considering wellfield design, production expectations, and long‐term management strategies for radial collector well production during drought, low streamflow, and times when high concentrations of nitrate‐N or organic pesticide compounds in the river may limit production options.

Assessment of the optimum location and hosting capacity of distributed solar PV in the southern interconnected grid (SIG) of Cameroon

ABSTRACT Cameroon’s electricity mix is dominated by hydropower sources despite the huge potentials of other sources like solar. The over-dependence on hydropower has led to frequent load shedding especially in the dry season as a result of low water levels. Interestingly, the government plans to diversify her power mix and provide sustainable energy to Cameroonians. It is in this framework that this study evaluates the integration of solar PV into the Southern Interconnected Grid of Cameroon using dynamic analysis. The ETAP tool was used in developing the model. A power loss assessment was done through successive injection of solar PV into the candidate busbars while monitoring the active power losses in the grid. Then, a transient stability analysis was conducted so as to assess the grid’s response to induced instability after the penetration of large-scale solar PV. The study showed that the use of static performance indices to evaluate the solar PV hosting capacity do not safeguard the grid’s technical robustness. The results indicated an optimum solar PV penetration level of 30% (211.8 MW) at the Ngousso 93 kV busbar. The findings will be useful to system operators and regulators in developing low-carbon pathways in the electricity network in Cameroon.

Formation of Dichlorine Monoxide for Organic Pollutant Degradation by Free Chlorine in High Chloride-Containing Water

Several ppm levels of free chlorine in high chloride-containing water of no less than 0.20 M show remarkably high degradation rate constants toward carbamazepine (kCBZ′). Dichlorine monoxide (Cl2O) was identified to be responsible for the high kCBZ′. Cl2O degrades aromatic pollutants connected to more electron-donating functional groups faster when comparing kCl2O to 1,4-dimethoxybenzene, bisphenol A, benzoic acid, and CBZ. However, its formation at low free chlorine levels in high chloride-containing water cannot be explained by our current knowledge. We proposed an alternative Cl2O formation mechanism, in which chloride transforms hypochlorous acid/hypochlorite (HOCl/ClO–) to dichlorine (Cl2) and polychloride monoanions (Cln–), which then react with HOCl/ClO– to form Cl2O. Decreasing pH from 8.60 to 4.33 increases Cl2 concentrations and thus generates about 600× higher Cl2O concentrations. Weak acid anions, for example, phosphate and bicarbonate, are strong nucleophiles assisting the Cl2O hydrolysis, but their presence at the testing conditions does not much affect kCBZ′. The proposed alternative Cl2O formation mechanism reveals the roles of chloride in shifting the equilibrium toward the Cl2O formation, allowing the simple chlorine addition strategy to degrade recalcitrant organic pollutants in high chloride-containing wastewater. It may also change our understanding of the speciation of different free chlorine species and their impacts on the DBP formation in high chloride-containing wastewater.

Rhine low water crisis: From individual adaptation possibilities to strategical pathways

IntroductionIn 2018, the Rhine transport sector experienced an unprecedented low water crisis, during which large cargo vessels were no longer able to navigate on certain sections of the river. This led to a major disruption in inland waterway transport. This article aims at questioning how the crisis acted as a stimulus for port authorities and their customers to consider the risks for their assets and operations and as a window of opportunity for creating a new collective and for defining “solutions.”MethodologyInspired by the Impact Chain methodology, a step-by-step protocol integrating focus groups and interviews, was applied so that stakeholders affected by low waters can identify their individual and common vulnerability and define possible ways of acting (pathways).ResultsOne of these pathways, the transitional infrastructural pathway, targets to increase the water level and overcome low water levels (use of Lake Constance as a water reservoir or creation of new water storage areas; deepening of the channel at Kaub and Maxau). It appears as the most suitable because it is a technical, well-controlled process that provides a comfortable solution in the short term. It exemplifies the lock-ins set by infrastructure.DiscussionHowever, the participative approach also highlights the fundamental challenge of developing new processes and new intermodal organizations in the long term.

Groundwater Vulnerability Assessment Phenomenon using DRASTIC & Modified DRASTIC Modeling validated with Nitrate Concentration.

<p>Urbanized areas groundwater vulnerability and contamination are serious issues that require due attention. There are other models, notably the DRASTIC models employed to assess the vulnerability of groundwater. In a modified version of the DRASTIC model known as anthropogenic influence was incorporated into DRASTICA as a model parameter. The research used a cutting-edge methodology to define the anthropogenic employing satellite data of nighttime lighting to have an impact using human settlements as a stand-in and the Palani Taluk's surrounding land use/landcover. The spatial integration of various parameter maps was done using a geographic information system. According to data on groundwater vulnerability to pollution, around 29.98% of the area is in a very high vulnerability zone, followed by 23.68% of area covers high vulnerability, 25.18% comes under the range of moderate vulnerability, 12.14% covers the area in the zones of low vulnerability, and 8.97% area covers the total area in the ranges of very low vulnerability. Utilizing the amount of nitrate in ground water, the findings were confirmed. It was determined that in an urban environment, the suggested DRASTICA model achieved enhanced than the conservative DRASTIC model. The classifications are as follows: extremely high, high, medium, and low. Very high Vulnerability zones account for 214 values in Palani taluk, the research region, whereas very low vulnerability zones account for 3 values in Palani taluk. Urbanization index showed that anthropogenic impact and the depth of the water table had a substantial impact on groundwater susceptibility to contamination, indicating that manmade effect must be carefully taken into consideration in such studies. This study's modified-DRASTIC/DRASTICA model will aid in better classifying groundwater sensitive areas to contamination where manmade pollution is high, especially in and near metropolitan centers. The groundwater susceptibility possible map that is produced can be more successfully used as the main tool for managing, organizing, and safeguarding groundwater resources. Low nitrate concentrations are found in forests and arid terrain, whereas high nitrate values are found in urban areas. The majority of the Palani taluk has low to moderate nitrate concentrations. The Melkaraipatty and Thalaiyuthu Palani Taluk's urban areas are considered by high sensitivity because of low water levels and strong manmade effect.</p>

Temperature and precipitation control the seasonal patterns of discharge and water isotopic signals of the Nyang River on the southeastern Tibetan Plateau

River hydrology on the southeastern Tibetan Plateau (SETP) is particularly sensitive to climate change, through the serious impacts of the decline in Indian summer monsoon (ISM) rainfall and the accelerated melting of snow and glaciers during the recent decades. Investigating the effects of meltwater and rainfall on the seasonality and quantity of river runoff in the region is crucial for improving regional hydrological monitoring and water management, and water stable isotopes can provide an effective method. Based on the event-based data of precipitation and river water isotopes, river discharge and meteorology monitored at a hydrometric station of the Nyang River on the SETP in 2011, we show that river discharge has a strong reliance on temperature and precipitation simultaneously through their controls on the meltwater and rainfall runoff, and river water deuterium excess (d) and δ18O potentially track the meltwater and rainfall effects separately. The seasonal signals of river discharge and isotopic data provide evidence that meltwater is the key factor of river discharge and isotopic changes during the pre-ISM season (low water level period) and ISM rainfall during the early to mid-ISM season (growing and high water level period) but key factors are not clear during the mid to post-ISM season (recession period). These inferred seasonal runoff source relationships are in close agreement with the runoff source contributions estimated using a season-specific δ18O-d mixing model approach. Specifically, the result suggests meltwater contributes ∼28 %, ∼41 % and ∼25 % of the total river runoff, and snowmelt does make a major contribution to the meltwater (compared to glacier melt) during the three individual hydrological periods. This study investigated the event-based river discharge and isotopic responses to temperature and precipitation and the relevance of seasonal meltwater and rainfall effects for a representative basin on the SETP, and we propose that long-term isotopic record of river water in this region may document catchment changes in runoff source relationships (especially snowmelt vs ISM rainfall).

Scouring effect of the middle and lower reaches of the Yangtze River and its impact after the impoundment of the Three Gorges Project

三峡及其上游干支流梯级水库建成运用后,大坝下游“清水下泄”引起了长江中下游河道发生长时间、长距离的冲刷。2001-2021年期间宜昌至长江口已累计冲刷了50.3亿m³,需厘清河道冲刷对河势、防洪、航运等方面产生影响。分析表明:三峡工程运用后,长江中下游河势总体稳定,弯道段出现切滩撇弯、汊道段出现塞支强干等现象;河道槽蓄量的持续增加,进一步增大了河道调蓄和行洪能力,但水流顶冲点的变化和近岸河床的冲刷下切,使得河道崩岸频发,并影响河势稳定和防洪安全;在河道冲刷、河势控制与航道工程综合作用下,长江中下游航道条件总体得到改善,但河道不均衡冲刷使得坝下游砂卵石河段出现“坡陡流急”,沙质河段出现洲滩散乱、航槽移位等现象,影响航道条件;同流量下枯水位呈下降态势,逢极枯年份影响长江中下游用水安全;江湖关系发生新变化,“三口”分流道由原淤积转为冲刷,两湖湖区水位不同程度的降低,枯水位出现时间有所提前,不利于湖区水资源和生态环境的安全与可持续发展;三峡工程实施枯水期补水调度和“压咸潮”调度以及长江口北支淤积减缓,对于遏制长江口咸潮入侵有利,入海泥沙显著减少引起长江口近岸河床冲刷,影响沿岸码头的安全运行。;After the construction of cascade reservoirs in the Three Gorges and its upper reaches, the downstream clear water of the dam was discharged, and a long-term and long-distance erosion occurred in the middle and lower reaches of the Yangtze River. From Yichang to the Yangtze Estuary, a total of 5030 million m³ was scoured. Under the background of large-scale erosion in the middle and lower reaches of the Yangtze River, it has a profound impact on river regime, flood control and shipping. The analysis shows that the river regime in the middle and lower reaches of the Yangtze River is generally stable, and the river regime in some parts of the river changes greatly, resulting in the phenomenon of beach cutting and bending, and the phenomenon of strong trunk. The increase of channel storage capacity increases the capacity of river discharge and flood storage, but the change of flow top scour point and the erosion of nearshore riverbed also make the river bank collapse frequently, affecting the stability of river regime and flood control safety. Under the combined action of channel scour, river regime control and channel engineering, channel conditions in the middle and lower reaches of the Yangtze River improved overall. However, due to the unbalanced scouring of the river channel, the sandy pebble river section in the downstream of the dam has a 'steep slope and rapid flow’, and the sandy river section has phenomena such as scattered beaches and channel displacement, affecting the channel conditions; the continuous erosion of river bed results in the decrease of low water level, which affects the water supply safety of life, production and ecology along the middle and lower reaches of the Yangtze River in extremely dry years. The relationship between rivers and lakes has undergone new changes. The three diversion channels have changed from original siltation to erosion. The water levels in the two lakes have decreased to varying degrees, and the low water level has appeared earlier, which has adversely affected the water resources and ecological environment in the lake area. The regulation of water replenishment and saltwater intrusion in dry season of the Three Gorges Project and the slowing down of siltation in the north branch are beneficial to the control of saltwater intrusion in the Yangtze Estuary. The sediment discharged into the sea from the Yangtze Estuary is significantly reduced and the riverbed near the Yangtze Estuary is scoured strongly. It seriously threatens the safety of the main structure of coastal enterprise wharf.

Changes in Radiation Exposure Rate of Fish of the Cooling Pond of the Chornobyl NPS and Lake Azbuchyn after Water Level Lowering

Changes in the absorbed dose rate of external and internal exposure of the representatives of fish fauna of the cooling pond of the Chornobyl NPS and Lake Azbuchyn after the interruption of water supply into the cooling pond at the end of 2014 were investigated in 2014-2021. Changes in hydrological regime resulted in the decrease in water level in the cooling pond by 6.5-7.0 m, whereas in Lake Azbuchyn - by 2.5-3.0 m. In this case, <sup>90</sup>Sr concentration activity in the water and biota increased. It has been found that in 2021 dose load from the incorporated <sup>90</sup>Sr on fish of the cooling pond increased on the average by a factor of 4.5, whereas in Lake Azbuchyn - by a factor of 7.5 as compared to previous period (prior to a decrease in water level). The external dose rate for fish of the cooling pond remained almost unchanged, whereas in Lake Azbuchyn it increased as a result of replacing littoral and sub-littoral zones of the lake with the sections of the bottom characterized by an essentially higher level of radio-nuclide contamination.

Prediction models for manganese, iron and ammonium in raw water for a drinking water treatment plant Butoniga (croatia)

Drinking water treatment plant Butoniga is one of the main water supply facilities for potable water in Istria (Croatia). Water for treatment process is captured from the Butoniga reservoir which is a small and relatively shallow reservoir. As such, the reservoir is very sensitive to eutrophication and degradation processes caused by climate change and human activities in the watershed. In summer months during tourist season, when at highest water demand and lowest water level at the reservoir, the water temperature is the most critical parameter during treatment process. To capture colder water, raw water for treatment is taken from the lowest water intake, i.e. from the deepest layer in the Butoniga reservoir. This layer has another problem, namely increased concentrations of manganese, iron and ammonium under lower pH values. This study provides prediction models for manganese, iron and ammonium for seven days in advance, which are some of the most critical parameters during summer months and have significant influence on treatment process of raw water. For modelling purposes, machine learning software Weka was used to build models in form of model trees. Obtained prediction models for manganese, iron and ammonium have high accuracy compared to the measured data with a good prediction of the peak values. Therefore, obtained models can help in optimization of the treatment processes at the treatment plant, which are depending on the quality of raw water in Butoniga reservoir.

Air entrainment and transport in a bottom outlet controlled by a cylindrical gate

This study deals with a bottom outlet that causes significant surges at both the inlet and exit. The bottom outlet comprises an intake, a vertical shaft and a tunnel underneath the rockfill dam and a submerged exit. In the intake tower, a cylinder gate controls hexagonal openings near the reservoir bottom. Operations during the dam construction show that discharges at a low reservoir water level result in upsurges of air-water mixture within the hollow gate cylinder and blowouts in the tailwater. To understand the flow behaviors, 3D CFD modeling is performed to examine air entrainment at the intake and transport down the waterway. Both low and high-water levels are simulated, and the air-water flow phenomenon is reproduced. In both cases, air pockets are generated, which undergo accumulation and breakup process. When moving downstream, they could cause severe surface fluctuations, even blowouts. Consequently, engineering solutions are required to address this issue. The aim of this study is to provide basis for risk assessment of outlet operations and potential rehabilitation measures.