Hydraulic Relationships Research Articles

Development and evaluation of hydraulic geometry relationships for large Brazilian river basins

ABSTRACT River cross-section characteristics are not available for many regions of the world, and they are generally expressed as hydraulic geometry (HG) relationships. These relationships usually represent average characteristics of a region, which can generate biased estimates in smaller basins. Therefore, to improve the representation of river channel geomorphological characteristics, the objective of this study was to use a large database of river cross-section geometries to refine HG relationships for five river basins in Brazil. HG relationships were developed for the entire basins and for hydraulically homogeneous regions, obtained through a geographical convenience method. The relationship between the coefficients of the geometric relationships and morphoclimatic characteristics was assessed, showing a trend between precipitation and slope and the coefficients of the depth relationships. The estimated bankfull width and depth values were also compared to observed data and global datasets, showing an improvement in estimates with the more refined HG relationships.

Interrelationships and Environmental Influences of Photosynthetic Capacity and Hydraulic Conductivity in Desert Species Populus pruinosa

An improved understanding of the mechanisms underlying plant adaptation to habitat heterogeneity can be achieved by clarifying the climate-driving factors of the hydraulic and photosynthetic traits of different populations. With a focus on Populus pruinosa Schrenk, which is the predominant tree species in the desert riparian forests of the Tarim Basin, Xinjiang, this study investigated the hydraulic and photosynthetic trait relationships and their interactions with environmental factors in 11 P. pruinosa populations using a Pearson correlation analysis, plant trait networks, a redundancy analysis, and a least squares linear regression analysis. The results showed that the degree of variation in the hydraulic traits was higher than that in the photosynthetic traits. The net photosynthetic rate (Pn) showed a significantly positive correlation with leaf-specific conductivity (Kl) and the Huber value (Hv). The Hv exhibited a significantly positive correlation with the water-use efficiency and Kl, and the branch–leaf mass ratio significantly affected the hydraulic traits. The groundwater depth (GD) in natural P. pruinosa forest habitats ranged from 3.4 to 7.9 m. With an increase in the annual average temperature, the hydraulic conductivity of the xylem significantly increased; with an increase in GD, Pn and Kl significantly decreased. The temperature annual range, temperature seasonality (standard deviation), min temperature of the coldest month, and GD were significantly correlated with the diameter and average path length of the overall trait network parameters, and these environmental factors affected the coordination of the functional traits of P. pruinosa.

Investigating the Hydrological Relationship between the North Taihang Tunnel and Tianshengqiao Nine Falls

The impact of a tunnel construction on the groundwater system depends on various parameters and cannot be easily predicted. Along these lines, a deep understanding of the hydrological relationship between tunnels and surface water is considered of vital importance for ensuring safety during railway construction. Upon completion, the North Taihang Tunnel will be one of four extra-long railway tunnels running through the natural ecotope and level-3 protection areas of the Tianshengqiao National Geological Park in Fuping County, Hebei Province. It will be 1 km away from the Tianshengqiao Nine Falls, which is known as a breathtaking landscape feature in Northern China. Local government, societies, and railway design units have raised concerns about whether the construction and operation of the North Taihang Tunnel will affect the Tianshengqiao Nine Falls. To effectively address this issue, in this work, hydrogeological mapping and hydraulic potential-energy calculations were performed in conjunction with hydrochemical and geological structure analyses. The groundwater system units in the study area were divided and the water source of the nine-level waterfall was determined retrospectively. In addition, the recharge of groundwater to the nine-level waterfall was calculated, the hydrogeological properties of the linear structure were analyzed, and the dominant channels of underwater discharge in surface water were compared and studied. The extracted results indicated that: (1) The Tianshengqiao Nine Falls represent a seasonal fall landscape, which is mainly supplied by surface water formed by precipitation and a low proportion of groundwater supply. (2) The water bodies of the North Taihang Tunnel project and Tianshengqiao Nine Falls belong to two independent groundwater systems. (3) No linear structure that connects these two groundwater systems has yet been discovered. It is widely accepted that a minor possibility of hydraulic connection might be present between the North Taihang Tunnel and Tianshengqiao Nine Falls. This work analyzed the water quantity of Nine Falls, determined the hydraulic relationship between the tunnel project and the waterhead of the Nine Falls, and addressed all stakeholder concerns. The conclusions could provide technological support for the scheduled construction projects.

Monthly hydraulic geometry relationship quantification with environmental LAI by utilizing sentinel data: A case in Jingjiang reach of the Yangtze River

This study presents a novel approach for quantifying the dynamics of monthly hydraulic geometry relationships in the Jingjiang reach of the Yangtze River by integrating leaf area index (LAI) data as an indicator of riparian vegetation. A comprehensive system of ordinary differential equations (ODEs) couples traditional power-law hydraulic geometry equations with LAI, capturing the influence of erosion control on channel morphology. The periodic delayed response theory and automatic differentiation techniques are employed to enhance the modeling framework’s capabilities. Calibration and verification demonstrate the models’ effectiveness in capturing overall trends in discharge, width, and depth dynamics, outperforming traditional constant-parameter approaches. However, model predictive abilities are limited under extreme climate conditions due to training on normal climate data. Key assumptions, including the periodic delayed response theory’s neglect of peak discharges, simplified representation of artificial cut-offs, and reliance on remotely sensed data with limited local validation, introduce uncertainties. The proposed modeling framework shows potential for broader application to other river systems with appropriate adjustments. Future research could incorporate additional environmental factors, integrate models across scales, couple with advanced simulation techniques, and expand stability assessments beyond the riverbed index. By addressing related challenges, this integrated approach lays a foundation for enhancing understanding of river morphodynamics and channel stability.

Multistage Stochastic optimization for mid-term integrated generation and maintenance scheduling of cascaded hydroelectric system with renewable energy uncertainty

The uncertainties resulting from the escalating penetration of renewable energy resources pose severe challenges to the efficient operation of modern power systems. Hydroelectricity is characterized by its flexibility, controllability, and reliability, and thus becomes one of the most ideal energy resources to hedge against such uncertainties. This paper studies the mid-term integrated generation and maintenance scheduling of a cascaded hydroelectric system (CHS) consisting of multiple cascaded reservoirs and hydroelectric units. To precisely describe the mid-term water regulation policies, the hydraulic coupling relationship and water-energy nexus of CHS are incorporated into the proposed optimization model. The uncertainties of natural water inflow and the power outputs of wind/solar energy generation are taken into consideration and captured via a stochastic process modeled by a scenario tree. A multistage stochastic optimization (MSO) approach is developed to coordinate the complementary operations of multiple energy resources, by optimizing the mid-term water resource management, generation scheduling, and maintenance scheduling of CHS. The proposed MSO model is formulated as a large-scale mixed-integer linear program that presents significant computational intractability. To address this issue, a tailored Benders decomposition algorithm is developed. Two real-world case studies are conducted to demonstrate the capability and characteristics of the proposed model and algorithm. The computational results show that the proposed MSO model can exploit the flexibility of hydroelectricity to efficiently respond to variable wind and solar power, and reserve water resources for the generation in peak months to reduce the consumption of fossil fuel. The proposed solution approach also exhibits promising computational efficiency when handling large-scale models.

Evaluation of vulnerable zones to water pollution in the lower Soummam alluvial aquifer, Bejaia, Algeria

Abstract Understanding the critical relationship between the Soummam River and its alluvial aquifer is crucial for the protection of this vital water resource. The approach is based on monitoring the spatial and temporal evolution of physico-chemical parameters and identifying their origin through correlation with the geology and piezometry of the alluvial aquifer; this will be achieved using differential gauging and hydrogeochemical tracing. This will provide valuable information for the management and protection of this precious water resource. The case study focuses on the alluvial aquifer of the lower Soummam Valley in Bejaia, Algeria, where a unique natural barrier upstream creates a close hydraulic relationship between the river and the aquifer. This allows for water exchange, which we investigated through two sampling campaigns (high and low water) at 32 water points (boreholes, wells and stations). By tracking the movement of special chemical tracers in both the Soummam River and the underlying alluvial aquifer, this study confirms a direct hydraulic connection between them. This means that water can flow from the river into the aquifer, highlighting the potential risk of water pollution. This has helped us to identify areas where pollution from the river could seep into the groundwater, threatening the drinking water supply.

Hydraulic Relationship between Hulun Lake and Cretaceous Confined Aquifer Using Hydrochemistry and Isotopic Data

Hydraulic Relationship between Hulun Lake and Cretaceous Confined Aquifer Using Hydrochemistry and Isotopic Data

Assessments of groundwater recharge process and residence time using hydrochemical and isotopic tracers under arid climate: Insights from Errachidia basin (Central-East Morocco)

The aquifer systems in the Errachidia basin, located to the south of the High Atlas limestone, are constituted by three superimposed and exploitable aquifers (Senonian, Turonian, and Infracenomanian). These aquifers hold economic significance for the central-east region of Morocco. This area experiences an arid to Saharan climate characterized by low precipitation, high temperatures, and very high evaporation. It is one of the most exposed and vulnerable regions to climate change in Morocco. The low local rainfall cannot explain the recharge of the deep aquifers. However, the significant spring discharges from these aquifers indicate the existence of other recharge contributions.The aim of this study is to elucidate the recharge processes of the Cretaceous aquifers in the investigated basin, clarify hydraulic relationships between them and the Jurassic aquifers of the High Atlas Mountains and estimate the residence time of groundwaters. Water samples from aquifers are collected and analyzed for chemical and isotopic elements. Several statistical methods (SOM, discriminant factorial analysis, CPA) are employed. The results reveal that many samples from different aquifers exhibit clear similarities in chemical characteristics, providing evidence of water transfer between aquifers. Isotopic findings are consistent with chemical characterization and mineralization anomalies.Recharge of the investigated aquifers originates from the Jurassic limestone of the High Atlas Mountains, facilitated by the karstic nature of the Jurassic in contact with the permeable formations of the Cretaceous basin. Age dating results, using 3H and 14C values, confirm that most of the investigated groundwater results from a mixing of old and recent recharges. This process of groundwater renewability is relevant. All the findings are valuable for decision-makers to enhance their understanding of the aquifer system's functioning and inform sustainable management strategies for future sustainability.

Machine learning facilitates connections between soil thermal conductivity, soil water content, and soil matric potential

Properly understanding the strongly coupled thermal and hydraulic properties of porous media is crucial to interests in different fields, e.g., agriculture, building physics and meteorology. Previous studies generally consider the thermal and hydraulic properties independently, specifically, the soil thermal conductivity curve and the soil water retention characteristics curve as methods to connect such process are unavailable or untested. In an effort to test methods based on machine learning (ML) to effectively integrate the soil thermal conductivity (λ), matric potential (ψ) and water content (θ), 2328 measurements from 43 soils were compiled using ML algorithms. Five ML algorithms, including random forest-RF, gradient boosting decision tree-GBDT, support vector machine-SVM, multiple linear regression-LR and backpropagation neural network-BPNN, based on the balanced dataset with synthetic minority over-sampling technique were trained, validated and tested to establish the λ(ψ) and λ(θ) relationships. Results demonstrate that, ML algorithms perform better than empirically based methods to optimize the thermal and hydraulic relationship. The selection of ML algorithms has a significant influence on the coupling relationship and should be taken into account. GBDT performed superior for small soil hydrothermal datasets (Testing set: Nash-Sutcliff efficiency-NSE = 0.9999 and Root Mean Square Error-RMSE = 0.0144 W m−1 K−1; independent verification: NSE = 0.7122 and RMSE = 0.2726 W m−1 K−1), while BPNN is limited by the amount of data with NSE = 0.9970, RMSE = 0.0790 W m−1 K−1 of Testing set.

Use of isotope techniques to evaluate the recharged ability of the upper Pleistocene aquifer in the Nambo Plain

In the Nambo Plain, the monitoring data on dynamics and quality of groundwater has shown declining signs in quantity and quality both in the existing groundwater aquifers, and the exploitation of groundwater in recent time is believed to be a cause of this decline. That shows the need for further research, especially on the modern recharge ability of the existing groundwater aquifers, to re-evaluate the groundwater potential of the region. For that purpose, isotope techniques are applied to evaluate the recharge ability of the upper Pleistocene aquifer, an important source of water supply in rural areas in the Nambo Plain.
 In this study, groundwater, river water and rainwater samples were collected and analyzed for stable isotope composition, tritium, radiocarbon and major hydro-chemical parameters. Data on stable isotope composition in groundwater are used to define the origin of groundwater while tritium and 14C content are used to determine groundwater age and to predict the aquifer’s recharge zone; and in combining with the stable isotope composition and tritium content of river water to evaluate the dynamic relationship between river water and groundwater.
 The obtained results show that: i) Groundwater in the study aquifer is originated from meteorological water and formed at different stages. ii) The high 3H and 14C content in some groundwater samples indicate that the aquifer has modern rainwater infiltrated as a recharge source. iii) The similarity of stable isotope composition in the Vam Co river water and groundwater adjacent to the river shows that there is a hydraulic relationship between them. This is an important basis for assessing the recharge ability to the qp3 aquifer of the Vam Co river water.

Investigating the Influence of the Relative Roughness of the Riverbanks to the Riverbed on Equilibrium Channel Geometry in Alluvial Rivers: A Variational Approach

The roughness of a river’s boundary significantly influences the sediment transport process and the ultimate configuration of the river’s stable cross-section. This interplay between boundary roughness and river morphology is crucial to a river’s overall behavior and form. This study aims to analyze the influence of the relative roughness of riverbanks to a riverbed λ on the equilibrium form of alluvial rivers using a variational method. The results show the following: (1) As the parameter λ transitions from smaller to larger values, noteworthy variations are observed in a river’s characteristics. Specifically, there is a discernible reduction in the calculated maximum sediment discharge, coupled with a corresponding expansion in the optimal width–depth ratio. For instance, when λ changes from 1 to 0.1, the optimal width–depth ratio increases by 45%, while the calculated maximum sediment discharge experiences a decrease of 1.62%. (2) An examination of hydraulic geometric relationships, derived by assigning distinct values to the relative roughness of riverbanks to the riverbed, highlights the significant influence of this relative roughness on the ultimate equilibrium configuration of the river channel. Remarkably, this effect remains consistent and stands independently of other variables such as sediment discharge, flow discharge, channel gradient, and sediment size. (3) The critical and average hydraulic geometric relationships deduced in this study closely align with previous research findings. Notably, this research contributes to addressing the existing gap in understanding the mechanistic underpinnings of how river boundary conditions impact the equilibrium forms of rivers, thereby advancing our knowledge of river morphology. Nevertheless, it is imperative to emphasize that while this study provides valuable theoretical insights, the practical application of these findings in the context of river morphological evolution necessitates further in-depth research. It calls for a more comprehensive exploration of the transition from theoretical constructs to real-world applications, thus promoting a deeper understanding of the dynamics that shape river systems.

Groundwater chemistry and isotope for interpreting the hydrogeological conditions and hydrochemical evolution of multilayer aquifer system of Donghai island, China

Groundwater is generally important water resource for islands. Groundwater recharge source and its hydrochemical characteristics are vital issues for the sustainable development and management of island groundwater resources. In this study, taking Donghai island which is featured with multi-layer aquifer structure as an example, by comprehensive using of statistical analysis, stable isotope (2H-18O), Gibbs diagram and ion ratio graph, we conducted a comprehensive hydrochemistry investigation for the groundwater in the shallow aquifer (i.e., phreatic and feeble confined aquifers) and middle confined aquifer of this island. And the hydrochemical characteristics, recharge sources, hydrogeochemical processes and source of element components of groundwater in different aquifers of Donghai island were identified. The results show that the major ions and TDS of the shallow groundwater are higher than those of the confined groundwater, and that those aquifers have not suffered significant seawater intrusion. The main hydrochemical types of shallow groundwater and confined groundwater are Cl·SO4-Ca·Na and HCO3-Na·Mg, respectively. Different hydrochemical types and chemical component concentrations between these two aquifers indicate that the hydraulic relationship between aquifers is relatively weak. The results of 2H-18O stable isotope and deuterium excess indicate that the shallow groundwater originated from local precipitation and that the recharge period of the confined groundwater is different from the shallow groundwater. Results of ion ratio reveal that the island groundwater hydrochemistry is mainly controlled by the water-rock interaction, featuring with dissolution of silicate rocks (such as sodium feldspar, potassium feldspar, calcium feldspar and biotite). In addition, cation exchange is also an important hydrogeochemical process controlling the hydrochemical composition of the confined groundwater. The results will be helpful for understanding of the local island hydrogeology and be supportive for the groundwater resources quantitative research such as numerical modeling for Donghai island.

Development, application and comparison of coupling techniques for modeling the hydromechanical behavior of unsaturated soils

This paper presents formulations for modeling the hydromechanical behavior in unsaturated soils using different coupling techniques. For this purpose, hydraulic constitutive relationships based on classical empirical models and mechanical constitutive relationships based on generalized effective stress are adopted. The coupling terms are defined using fixed stress rates. They are included in finite-element formulations adapted for using four coupling techniques: the fully implicit, the sequential-iterative, the sequential-explicit, and the one-way. The algorithms proposed for each technique are implemented in a numerical framework that manages the solution process considering the same simulator, enabling fair comparisons among all methods. Numerical tests are carried out for each coupling technique's stability, accuracy, and performance. According to the results, the proposed techniques can be adopted to simulate properly the hydromechanical behavior of unsaturated soils, including soil expansion and collapse under wetting.

Herb hydraulics: Variation and correlation for traits governing drought tolerance and efficiency of water transport

Hydraulic traits dictate plant response to drought, thus enabling better understanding of community dynamics under global climate change. Despite being intensively documented in woody species, herbaceous species (graminoids and forbs) are largely understudied, hence the distribution and correlation of hydraulic traits in herbaceous species remains unclear. Here, we collected key hydraulic traits for 436 herbaceous species from published literature, including leaf hydraulic conductivity (Kleaf), water potential inducing 50 % loss of hydraulic conductivity (P50), stomatal closure (Pclose) and turgor loss (Ptlp). Trait variation of herbs was analyzed and contrasted with angiosperm woody species within the existing global hydraulic traits database, as well as between different growth forms within herbs. Furthermore, hydraulic traits coordination was also assessed for herbaceous species. We found that herbs showed overall more negative Pclose but less negative Ptlp compared with angiosperm woody species, while P50 did not differ between functional types, regardless of the organ (leaf and stem). In addition, correlations were found between Kleaf and P50 of leaf (P50leaf), as well as between Pclose, P50leaf and Kleaf. Within herbs, graminoids generally exhibited more negative P50 and Ptlp, but lower Kleaf, relative to forbs. Within herbs, no clear pattern regarding hydraulic traits-climate relationship was found. Our analysis provided insights into herb hydraulic, and highlighted the knowledge gaps need to be filled regarding the response of herbs to drought.

Effects of season and slope orientation on stable isotopes of different water bodies in the subalpine shrub zone of the eastern Qilian Mountains in China.

The subalpine shrub zone of the Qilian Mountains is an important water-retaining area, and it is crucial to clarify the processes of its hydrological cycle. Therefore, based on the stable isotope values of different water bodies in the subalpine shrub zone of the eastern Qilian Mountains from May to October 2019, the characteristics of δD and δ18O of different water bodies and their hydraulic relationships with each other were studied. The results showed that the stable isotope values of precipitation exhibited the largest fluctuations, while they were the most stable for groundwater. Plant transpiration was stronger than the evaporation of other water bodies. The stable isotope of precipitation was enriched in high temperature and low humidity environments. Isotopic values of plant and soil water were higher and more stable on the semi-sunny slope than on the semi-shady slope. According to the stable isotopes, there was a strong hydraulic relationship between the different water bodies in the study area, and precipitation was the ultimate source of all of them. Precipitation replenished soil water through infiltration. Part of the soil water was absorbed by plants, while the rest continued to infiltrate to replenish groundwater. Groundwater and precipitation replenished the river water.

A Method for Calculating Water Demand for Sediment Transport Based on the Principles of River Dynamics

Sufficient water is pivotal in maintaining the stability of boundaries in sandy river systems. However the current methodologies employed for computing the water demand for sediment transport in rivers frequently neglect this component. This research utilizes data spanning 1960 to 2020 from seven principal hydrological stations located in the lower Yellow River to establish the correlation between key factors pertaining to the sediment transport capacity of flow. A closed equation system was established based on the principles of river dynamics to solve unknown hydraulic parameters. Finding a suitable hydraulic geometric relationship equation as a supplementary equation is a key step in constructing a closed equation system. The findings indicate that sediment transport water demands are 71.79, 133.24, 226.89, 286.12, and 313.6 × 108 m3, respectively, when sediment inflow is at 1, 2, 4, 6, and 8 × 108 t, with a bankfull discharge of 4000 m3/s. As the sediment inflow diminishes and the unit water demand for sediment transport increases, the sediment transport efficiency of the lower Yellow River reduces. The outcomes of this research can serve as a foundation for the joint operation of the Yellow River’s main and branch reservoirs, as well as for designing water resource allocation schemes within the basin.

Accelerating the Consolidation of Thickened Tailings Using Sand Co-Disposal

Only grams or kilograms of valuable resources are extracted for each tonne of ore processed, generating immense amounts of tailings. Returning tailings-containment dams to their equivalent pre-disturbance landscape state is many stakeholders’ acceptable management strategy. The depositing of thickened fluid fine tailings (FFT), which the industry has relied upon to develop geotechnically stable dry landscapes, has not materialised due to the low hydraulic conductivity of such placements. The addition of sand to thickened FFT is proposed to accelerate the consolidation of thickened FFT in a co-disposal scheme, and this study evaluates its impact. In the continuum of solid wastes from mining operations, sand is the next-larger-sized grade of solids after “fine” that is produced in high proportions. Blends of highly-plastic FFT and fine-grade sand tailings at varying sand-to-fine ratio (SFR) values were tested. Sand lowered the liquid limit but did not significantly affect the plastic limit of FFT. The changes in liquid and plastic limits for SFR ≥ 1 blends were under 5% of water content. The maximum unit weight for the co-disposal mixes was obtained at SFR 3. Despite increases in unit weights, hydraulic conductivity increased with increasing SFR, while the trend for compression rates was in the reverse order. Void ratio—effective pressure—hydraulic conductivity power law relationships at varying SFR were obtained from the consolidation measurements. The constitutive constants of these relationships were used to model settlement of 30 m deep pits over a 25-year period. For all the deposits studied, the dewatering converged to a maximum solids content characteristic of each SFR in the order 74, 85, 88, and 94% (w/w) for thickened FFT and SFRs 1, 2, and 3, respectively. The numerically calculated average solid contents of the deep-pit placements grew closer with increasing SFR becoming 59, 77, 82, and 86% (w/w), respectively. Balancing the consolidation-rate gains and the land footprint required for storage with SFR increase, the optimal composition for co-disposal for this material and similar tailings is SFR 1.

Assessment of the hydrogeochemical and isotopic characterization and hydraulic behavior of the Izeh complex karstic area, Khuzestan province, southwest Iran

Proper water resources management requires recognizing and evaluating the factors that affect the quantity and quality of water resources. The Ilam-Sarvak (Upper Cretaceous) and Asmari (Oligocene to Miocene) limestone- dolomite formations in the Zagros structural belt have formed a promising karst groundwater horizon. In the present study, the hydraulic relationship between the karst structures of the Izeh territory in the northeast of Khuzestan province was investigated using hydrogeochemical and isotopic information of springs and wells. The results enabled to understand various components influencing the recharge of water resources. In this study, samples were collected from the karst springs and wells of Mongasht, Shavish-Tanosh and Kamarderaz anticlines and Naal-e-Asbi (Horseshoe) syncline and meteoric water to understand the hydrochemical and isotopic characterization, and hydrogeological and hydraulic behavior of the Izeh karst system. The meteoric and groundwater samples were analyzed to determine major and minor ion concentrations and δ18O and δ2H isotope ratios. Isotopic content ranged from -31.6 to -2.9‰ and from -6.32 to -1.87‰ for δ2H and δ18O, respectively, and d-excess values were high and positive. The study of the isotopic content of water samples of springs and wells in the region shows three groups of water sources. The first group, related to the Mongasht anticline springs, has lower isotopic values, indicating that it is recharged by rainfall at high altitudes and snow melting. The isotopic value of the second group is richer than that of the first group, indicating rainfall recharge as well as groundwater mixing (ex­amples of Naal-e-Asbi syncline and Shavish-Tanosh anticline). The highest value in the third group (samples of Kamarderaz anticline) is attributed to evaporation and longer distance from the recharge site to the discharge point, as well as to the diffu­sion system. The trend of decrease in Sr+2 and increase in Ba+2 in the samples of dolomitic limestone formations (Shavish Ta­nosh and Mongasht anticlines) compared to the water samples of Kamarderaz anticline and Naal-e-Asbi syncline indicates the possibility that karst aquifers of the region are recharged from the Mongasht anticline and that there is a hydraulic relation­ship between these structures. D-excess and δ18O show a linear trend, illustrating the effect of altitude difference on isotopic content and recharge sources. The major and minor changes in the concentration of ions, the isotopic content of groundwa­ter and the relationship between TDS and δ18O and d-excess and δ18O indicate the mixing and recharging of karst aquifers (Shavish-Tanosh, Kamarderaz and Naal-e-Asbi aquifers) from the Mongasht karst aquifer and their hydraulic connection.

Determination of River Ecological Base Flow Based on the Coupling Relationship of Sediment–Water Quality–Biodiversity in Water Shortage Area of Northwest China

Maintaining the integrity of ecosystem service functions of rivers has become the top issue in the water shortage area of Northwest China. By combining the coupling relationship of sediment, water quality, and biodiversity and the hydraulic relationship of the section, we established a quantitative calculation method for the river ecological base flow, which is mainly divided into the following three steps: first, we determined the reasonable ecological flow velocity range of rivers via water purification, maintaining the river geometry and biodiversity; second, we combined the hydraulic relationship between the river ecological velocity range and the river ecological base flow to determine the protection target of the river ecological base flow; finally, we combined the remaining water volume of rivers and ecological base flow protection target of rivers to determine their protection rate. Take the Baoji section of the Weihe River as an example: the results show that the ecological base flow in the Baoji section of the Weihe River is [6.26, 9.17 m3/s] and [32.94, 38.93 m3/s] from October of this year to May of next year and from June to September, respectively, and the protection rates of the ecological base flow for five typical years are 62.47%, 41.10%, 16.16%, 15.07%, and 10.68%. These coupling methods can also be used in the world’s river basin, which has similar problems.

Natural and anthropogenic factors regulating fluoride enrichment in groundwater of the Nansi Lake Basin, Northern China

Excess fluoride (F−) in groundwater can be hazardous to human health of local residents who rely upon it. Beside natural sources, anthropogenic input may be an additional source to be considered. Twenty surface water and 396 groundwater samples were collected from the Nansi Lake Basin, with hydrogeochemical and isotope techniques employed to clarify the spatial variability, source, and the natural and anthropogenic factors regulating the occurrence of high F− groundwater. The factors responsible for elevated F− levels in surface water and deep confined aquifers are discussed based on their hydraulic relationship. Also a conceptual model of F− enrichment with different aquifer systems is put forward based on the geomorphic units of the basin. The results show that F− concentration is between 0.1 and 6.9 mg/L in the west of Lake, while ranged from 0.03 to 1.74 mg/L in the east of Lake. The hydrogeological setting and lithology are the primary factor determining the provenance of high-fluoride groundwater in the basin. Fluoride mainly originated from the dissolution of fluorine-bearing minerals, and is affected by the alkaline groundwater environment, cation exchange, adsorption, and evaporation. The landforms on the east side of Nansi Lake are low hills and piedmont sedimentary plains, where the aquifers consist of karst fissure water and overlying porewater. High F− groundwater is not observed in this area due to its rapid flow and Ca2+-enriched hydrochemical characteristics. The anthropogenic input (such as fertilizer application on farms and illegal industrial pollutant discharge), contribute F− to groundwater in varying degrees, especially in the shallow aquifers east of the lake and in some parts west of the lake. This work is a clear example of how natural processes together with human activities can affect the chemical quality of groundwater, which is essential to safeguard the sustainable management of water resources in semi-arid areas.