Groundwater Table Depth Research Articles

Estimation, modeling, and prediction of land subsidence using Sentinel-1 time series in Tehran-Shahriar plain: A machine learning-based investigation

Land subsidence (LS) is a major geologic hazard threatening most areas in Iran due to excessive groundwater extractions. The main objective of this study was to estimate LS applying PS-InSAR technique and then model and predict it through machine learning methods. Sentinel-1 time series images were used to retrieve LS from 2014 to 2019. Random forest regression (RFR) and artificial neural networks (ANN) were implemented to model LS of 2014–2017 using some conditioning factors including groundwater level decline, aquifer media, precipitation rate, slope, landuse type, depth to water table, distance from exploiting wells, distance from rivers and distance from faults as independent variables. The best calibrated method was used to predict LS over 2018–2019. In addition, all k-combinations (k=1: n, n is the number of factors) of conditioning factors were evaluated to identify the best combination resulting in the best output. The procedure was examined in the Southwest of Tehran and Shahriar plain, Iran. The maximum cumulative displacement values were 561.78 and 638.5 mm for Tehran and Shahriar, respectively. The accuracy assessment showed the RMSE value of 9.97 mm for LS retrieval. The experimental results of LS modeling indicated that RFR outperformed ANN, representing more robust and reliable results with the RMSE value of 1.35 mm for the both study areas. The investigation of the possible factor combinations showed that using the 4-factor combination consisting of precipitation, ground water table change and depth to water table along with distance from faults for S1 and the thickness of fine-grained soil layers (clay and silt) for S2 have presented promising results in modeling and predicting LS. Using all the conditioning factors, LS was predicted with RMSE value of 2.53 mm and 2.09 mm for S1 and S2, respectively. Using the 4-factor combination, however, the prediction RMSE increased by 0.13 mm and 0.04 mm for S1 and S2, respectively. This 5-percent difference can be ignored against decreasing the total cost of applying all factors. This study demonstrates the usability of processing Sentinel-1 data for LS retrieval and applying RFR for LS prediction.

Chemical characteristics of salt migration in frozen soils during the freezing-thawing period

Soil water and salt movement in freezing-thawing periods play an important role in the agricultural ecological environment. Field experiments show a non-synchronized movement of soil water and salt during the freezing-thawing period with no definite mechanism. In this study, the non-synchronization of water and salt movement in the frozen layer (0–1 m) was analyzed from the perspective of soil salt composition combining with the convection–diffusion theory. Field experiments were carried out during two freezing-thawing periods from 2017 to 2019 in Yonglian experimental station of Hetao Irrigation District in Inner Mongolia, China. The contents of soil moisture, salt and its components (Na, K, Ca, Mg, CO3, HCO3, Cl and SO4) were measured. The correlation analysis between storage increments of total salt and its components was carried out and the FREZCHEM model was used to calculate the soluble and solid salt components. During the freezing period, the soil water storage increased by 5.42% on average, while the soil salt storage decreased by 18.69%, showing the different migration directions of soil water and salt. The migration direction of each component of salt was not exactly the same with that of the total salt. The main components causing the storage increment of soil salt were different in the three saline soils. The solute concentration gradient of soluble salt reached 3.07 mol/(L·m), which caused stronger diffusion effect to result in downward salt migration, while the convection effect drove the soil water and salt to move upwards. This is the major reason for the non-synchronization movement of soil water and salt during the freezing-thawing period. This study provides new data and perspective to understand the soil water and salt movement during the freezing-thawing period in agricultural areas with shallow groundwater table depth.

Determination Of Groundwater Recharge Area In Raimanuk And Surroundings, Timor Island

The Raimanuk area in Timor, East Nusa Tenggara, is located in the Aroki Groundwater Basin. The decreasing quality and potential groundwater availability in the Aroki Groundwater Basin is feared due to its widespread use for household needs and agriculture. The lack of the groundwater recharge area map will pose an obstacle in policymaking regarding the management and preparation of spatial conservation areas in the Raimanuk Region. This study aims to determine the zone and classification of groundwater recharge areas in the Raimanuk area based on spatial data analysis. The groundwater recharge area can be determined using slope, river flow patterns, spring emergence, and groundwater table depth. The classification of the recharge area uses a scoring approach with an overlapping analysis of the parameter assessments, which are hydraulic conductivity, precipitation, soil cover, slope, and depth of unconfined groundwater. The result of the study is the groundwater recharge area map of Raimanuk. The groundwater recharge area is located in the Mandeu Hill area, which is the main recharge area. The groundwater discharge area is located in the Aroki plain area that can be the main recharge area.

FACTORS AFFECTING THE THICKNESS OF REPLACEMENT LAYER ON MEDIUM CLAY

Soil replacement is a common technique that can be used to increase the soil bearing capacity and reduce the expected settlement. The thickness of replacement layer depends on many factors such as: the applied stress, original soil properties, material of replacement layer and the cost of foundation works. However, until now the practical thickness of replacement is usually selected based on soil experts’ experience. This study proposed an optimization model to assist geotechnical engineers in predicting the optimum thickness and material type of replacement layer that satisfy the main design requirements, i.e. bearing capacity, consolidation settlement and cost considerations at the same time. The Evolutionary solving method that uses a variety of genetic algorithm and local search methods was used to solve the research problem. Furthermore, the effect of the thickness and properties of clay layer and the depth of ground water table on determining optimum type and thickness of replacement soil were investigated. The study evaluated the relationship between the replacement layer thickness and the total direct cost of foundation works and found that, the notion of increasing replacement thickness to decrease cost limitlessly was not viable and an optimal thickness was usually achieved.

Development and application of a new package for MODFLOW-LGR-MT3D for simulating regional groundwater and salt dynamics with subsurface drainage systems

Subsurface drainage systems have been widely used to help manage soil salinization worldwide. However, designing a subsurface drainage system requires predictions of regional groundwater and salt dynamics. While these dynamics can be obtained using MODFLOW’s drain package (DRN), this package requires that the drain conductance be specified, which is difficult to determine for subsurface drainage systems with different layout parameters, including the pipe spacing, depth and radius. In this study, a new subsurface drainage (SDR) package based on the Hooghoudt equation was developed within the MODFLOW-LGR-MT3D framework to simulate the effects of subsurface drainage pipes on groundwater flow and salt dynamics. The accuracy and applicability of SDR were tested by a synthetic case, a published indoor experiment and two field experiments. Comparison with indoor experimental data shows that the RRMSE of cumulative drainage volume was 5.08% and the RRMSE of groundwater table depth was 3.69%. The simulation results of outdoor experiment show that the RRMSE of drainage volumes of a single pipe ranged from 3.14% to 4.69%, and the relative errors of cumulative drainage volumes were below 6% and the relative errors of drainage discharge were 3.1–16.3%. The results demonstrate that SDR can accurately simulate leaching water and solute transport under transient flow conditions. The model was then applied to the Yonglian irrigation area of Inner Mongolia, China, for subsurface drainage system design, and 3 different layout schemes of subsurface drainage systems were presented. The total salt discharge increased by 38–54% after the application of the subsurface drainage system, 36–45% of which was discharged by subsurface drainage pipes. This study provides a pilot example for regional subsurface drainage system design.

An Indirect Approach Based on Long Short-Term Memory Networks to Estimate Groundwater Table Depth Anomalies Across Europe With an Application for Drought Analysis

The lack of high-quality continental-scale groundwater table depth observations necessitates developing an indirect method to produce reliable estimation for water table depth anomalies (wtda) over Europe to facilitate European groundwater management under drought conditions. Long Short-Term Memory (LSTM) networks are a deep learning technology to exploit long-short-term dependencies in the input-output relationship, which have been observed in the response of groundwater dynamics to atmospheric and land surface processes. Here, we introduced different input variables including precipitation anomalies (pra), which is the most common proxy of wtda, for the networks to arrive at improved wtda estimates at individual pixels over Europe in various experiments. All input and target data involved in this study were obtained from the simulated TSMP-G2A data set. We performed wavelet coherence analysis to gain a comprehensive understanding of the contributions of different input variable combinations to wtda estimates. Based on the different experiments, we derived an indirect method utilizing LSTM networks with pra and soil moisture anomaly (θa) as input, which achieved the optimal network performance. The regional medians of test R2 scores and RMSEs obtained by the method in the areas with wtd ≤ 3.0 m were 76–95% and 0.17–0.30, respectively, constituting a 20–66% increase in median R2 and a 0.19–0.30 decrease in median RMSEs compared to the LSTM networks only with pra as input. Our results show that introducing θa significantly improved the performance of the trained networks to predict wtda, indicating the substantial contribution of θa to explain groundwater anomalies. Also, the European wtda map reproduced by the method had good agreement with that derived from the TSMP-G2A data set with respect to drought severity, successfully detecting ~41% of strong drought events (wtda ≥ 1.5) and ~29% of extreme drought events (wtda ≥ 2) in August 2015. The study emphasizes the importance to combine soil moisture information with precipitation information in quantifying or predicting groundwater anomalies. In the future, the indirect method derived in this study can be transferred to real-time monitoring of groundwater drought at the continental scale using remotely sensed soil moisture and precipitation observations or respective information from weather prediction models.

Two-dimensional analytical solution for subsurface volatile organic compounds vapor diffusion from a point source in layered unsaturated zone

Although migration of subsurface volatile organic compounds (VOCs) from contaminant sources in unsaturated soil widely exists, the related analytical models are quite limited. A two-dimensional analytical solution is hence developed to simulate vapor diffusion from the subsurface contaminant source in the layered unsaturated zone. The contaminant source is simplified as a point source leaking at a constant rate. The influences of several important factors, including thickness of stagnant air layer, depth of groundwater table, source characteristics and soil layering characteristics, on vapor migration in subsurface soil are comprehensively investigated by the present model. Soil type does not affect the normalized vapor concentration profile for homogeneous soil, which is not valid for layered soil. The width and effective diffusivity of the upward diffusion pathway and downward diffusion pathway are favorable indexes to evaluate the intensity of subsurface vapor horizontal diffusion. The single-layer capillary fringe assumption overestimates the vapor plume, the assumption can give acceptable result for coarse soil while it is recommended to divide the soil into several layers based on the water-filled porosity profile for fine soil.

Evaluation of Water Content in Soils of Žitný Ostrov from the Point of View of Its Exploitation for Biosphere

The lithospheric zone between the soil surface and the first ground water horizon, respectively the ground water table, has a character of three-phase system. It consists of solid phase having fine to rough disperse granularity. This creates a structure of porous environment with characters that can be physically determined. The water occurs in pores in different forms of state and its bond with solid phase. Its energetic bond is clearly quantified by means of moisture retention curve. The gas phase fills pores with the water up to the value of the full porosity, i.e. it fills the part of pores that is not saturated with water. Therefore, this lithospheric zone is called the soil aeration zone. The volume of water occurring in the soil aeration zone corresponds to the concentration of water in the framework of hydrological cycle components. This water serves as the water resource for the vegetation cover. The data used for calculation were particular soil types in the area, depth of ground water table, hydrolimits (wilting point, point of decreased availability, field water capacity) and aeration zone thickness. The water content in the soil aeration zone between hydrolimits field water capacity (FWC) and wilting point (WP) is the critical interval of water content for vegetation cover in a given locality. Water from this interval is available for the vegetation cover. This water has no properties of free water, and plants have to have a developed root system and such suction pressure, that is able to overcome the bond between water and soil. Calculated results were verified with the help of monitored water content. Both calculated and measured values of soil water content in the aeration zone show that the water content is affected by appurtenant soil type. The human activity in a landscape directly affects the dynamics of this water resource, either from quantitative or qualitative viewpoint. This affect is demonstrated by changes of the ground water regime, i.e. changes of ground water table and amplitude of its fluctuation. The paper brings results of water content evaluation in the soil aeration zone in the Žitný ostrov area.

A parametric sensitivity analysis for prioritizing regolith knowledge needs for modeling water transfers in the West African critical zone

AbstractHard rock aquifers (HRAs) in West Africa (WA) are located within a thick regolith layer. The representation of thick tropical regolith in integrated hydrological models lacks consensus on aquifer geometries and parameter ranges. Our main objective was to determine the knowledge requirements on saturated hydraulic conductivity (Ks) to model the critical zone (CZ) of HRAs in WA. A parametric sensitivity analysis with a focus on the representation of the Ks heterogeneity of the regolith was conducted with a critical zone model (Parflow‐CLM [Community Land Model]) of the Upper Ouémé catchment in Benin (14,000 km2) at a 1‐ × 1‐km2 resolution. The impact of parameter changes in the near subsurface (0.3‐to‐5‐m depth) and in the deeper regolith aquifer (24‐ and 48‐m maximum depth) was assessed in five modeling experiments. Streamflow was largely dependent on Ks and on clay distribution in the near subsurface and less on the properties of the deeper subsurface. Groundwater table depths and amplitudes were controlled by vegetation and topography as observed on instrumented hillslopes and for Ks within the literature range. Experiments with higher Ks suggested a Ks threshold where dynamics become less determined by one‐dimensional vertical and more determined by lateral processes. Such heterogeneity impacts from smaller scales need to be accounted for when hydrological models are upscaled to larger domains (1‐ × 1‐km2 resolution or coarser). Our findings highlight the need for a new conceptual approach to represent clay distribution in order to develop catchment‐scale CZ models of HRAs in WA that capture the observed processes.

Modelling the Impact of Vegetation Change on Hydrological Processes in Bayin River Basin, Northwest China

Vegetation change in arid areas may lead to the redistribution of regional water resources, which can intensify the competition between ecosystems and humans for water resources. This study aimed to accurately model the impact of vegetation change on hydrological processes in an arid endorheic river watershed undergoing revegetation, namely, the middle and lower reaches of the Bayin River basin, China. A LU-SWAT-MODFLOW model was developed by integrating dynamic hydrological response units with a coupled SWAT-MODFLOW model, which can reflect actual land cover changes in the basin. The LU-SWAT-MODFLOW model outperformed the original SWAT-MODFLOW model in simulating the impact of human activity as well as the leaf area index, evapotranspiration, and groundwater table depth. After regional revegetation, evapotranspiration and groundwater recharge in different sub-basins increased significantly. In addition, the direction and amount of surface-water–groundwater exchange changed considerably in areas where revegetation involved converting low-coverage grassland and bare land to forestland.

The pesticide fate tool for groundwater vulnerability assessment within the geospatial decision support system LandSupport

The protection of groundwater resources from non-point-source pollutants, such as those coming from agricultural practices, is the focus of several European Directives, including the Water Framework Directive and the Pesticide Directive. Besides the environmental goals to be reached by the single EU member state, these directives clearly underline the role of experts in supporting planners and public authorities to fulfil these objectives. This work presents a new web-based, freely-available dynamical tool, named the pesticide fate tool, developed within the geospatial Decision Support system (DSS), LandSupport, for the assessment of groundwater vulnerability, specific for type of pollutant. The tool is based on the extended transfer function model, specifically expanded to consider the transport of reactive solutes, such as pesticides. The work describes the tool implementation for three case studies, with different spatial scales and pedo-climatic conditions: Valle Telesina, IT, Marchfeld, AT, and Zala County, HU. Principal inputs of the tool are: soil physical and hydrological properties, climate, groundwater table depth, type of crops and related pesticides. Results of the model are shown through the LandSupport GUI both as coloured maps, representing the relative concentration of pesticide at the arrival to the water table at the end of the simulation period, and as cumulative charts of the solute arrival at the depth of interest. The three case studies are shown as examples of application of the LandSupport DSS in supporting the Water and Pesticides directives, demonstrating that it represents a valuable instrument for public authorities, environmental planners, as well as agricultural extension services. For example, large differences are shown by soils in filtering the tetraconazole (99.9% vs 76%), a fungicide used in viticulture, or different percentage of arrival (0.32% and 0,01%) to the groundwater table are shown for two herbicides (Tribenuron and Florasulam) largely used to control annual dicotyledonous weeds.

Elevated salinity and water table drawdown significantly affect greenhouse gas emissions in soils from contrasting land-use practices in the prairie pothole region

Land-use practices can alter shallow groundwater and salinity, further impacting greenhouse gas (GHG) emissions, particularly in the hydrologically dynamic riparian zones of wetlands. Emissions of CO2, CH4, and N2O were estimated in soil cores collected from two prairie pothole region (PPR) sites with three adjacent land-use practices (i.e., annual crop = AC, pasture = PA, and short rotation willow = SRW) and treated with declining water table depths (2 to 26 cm), and salinity (S0 = control, S1 = 6 mS cm−1, and S2 = 12 mS cm−1) in a microcosm experiment. Land-use practices significantly (p < 0.001) affected GHG emissions in soils from both sites in the order of PA > AC = SRW. Compared to the control, emissions of CO2 and CH4 were significantly lower under higher salinity treatments (i.e., S1 and S2), while N2O was significantly higher (p < 0.05). Emissions under declining groundwater table depths were significantly (p < 0.001) variable and specific to each gas, indicating the impacts of shifted soil moisture regime. Overall, the CO2 and CH4 emissions increased up to week four and then decreased with declining water table depths, whereas N2O emission increased up to a maximum at week six. The soils from SRW had considerably lower global warming potential compared to AC and PA. Groundwater salinity in soils from contrasting land-use in the PPR has significant impacts on GHG emissions with potential for crucial climate feedback; however, the magnitude and direction of the impacts depend on hydrology.

The Use of Dual and Surge Irrigation to Improve The Efficiency of Surface Irrigation

A field experiment was conducted in a farm(5km northwest of Ramady City) during Autumn Season in a silty clay loam sedimentary soil. The ground water table depth is 120 cm. Field has divided into 10 strips(2.40x80)m with spaces 1m between strips and 2 m between replicates each strips has divided into 3 furrows (20 cm in depth, 80 m length,with 0.2% slop) with each others.Study factors included Contineous Irrigation (conventional), Dual Contineous irrigation, Contineous irrigation with two phases, Surge irrigation, Dual Surge irrigation Cycle ratio was 0.25 with time On-time 4 minutes and off-time 12 minutes for both dual surge irrigation and surge irrigation with discharge of 2 litter/sec. for both advance phase while the discharge after completing advance phase was 0.8 litter/sec. The plots were planted with corn(Zea mays L)and irrigated drainage water with salinity 5.8-6.2 ds/m, and Euphrates water (1.1-1.3 ds/m). Consumptive water use was calculated by Evaporation Pan method. Twenty test has been carried out for advance and recession of flow along furrow by using eight observation stations. Apportinity time and absorbed water depth in each middle furrow was calculated at each station. Practical and Theoretical relative yield of corn were calculated.Results showed that Dual Surge Irrigation system reduced of salty water used to complete advance phase with rate of 12.41% comparing with Dual Contineous irrigation system, The efficiency of Salt- water displacement proceeses downward increased by 11.56%. by the effect of fresh water under Dual surge irrigation system compared with Dual Contineous Irrigation system, The percentage fresh water saving reached to 44.94% and 51.30% in dual surge and dual Contineous irrigation system respectively, Insert Surge Irrigation technique on Dual Contineous Irrigation system leads to reduce salt- water advance phase time, late in recession time in Dual surge Irrigation and Surge Irrigation with the other treatments during advance and post- advance phase, distribution of Dual surge Irrigation system as compared with dual Contineous irrigation system in salt- water distribution efficiency during advance phase and uniformity of total absorption depth along the furrow for all testing months during the season, theoretical relative yield (RY%) has decreased gradually with increasing in depended depth for calculating the average soil salinity (ECe) with assumption of no mixing between fresh and saline water, practical relative yield exceeds the theoretical relative productivity when assuming the condition of mixing between fresh water and salt water, the practical relative yield has distinction on the theoretical yield at depth of 0-90-cm in Maas 1984 equation.

Effects of evolving salt precipitation on the evaporation and temperature of sandy soil with a fixed groundwater table

AbstractThe effects of salt precipitation on water and heat transport in soil have garnered considerable attention. However, salt precipitation growth on the soil surface and its influence on soil evaporation and temperature under a fixed groundwater table are not well understood. Therefore, the objective of this study was to investigate the impact of the evolution of salt precipitation on evaporation and temperature in sandy soils with a fixed groundwater table depth (20 cm). The laboratory experiment consisted of two treatments for sand columns: one with fresh groundwater, and the other with saline groundwater. Regions with salt precipitates expanded laterally and vertically whereby a salt crust was formed that disconnected from the soil. The lateral growth of salt precipitation had a minor impact on evaporation as the soil remained wet, while mostly being covered by the salt crust. However, the elevated salt crust caused a sharp decrease (&gt;60%) in the evaporation rate. Therefore, a new stage of saline soil evaporation was determined; the evaporation rate was further reduced by the elevated salt crust. Moreover, the soil profile temperature decreased when the soil was covered by the salt crust, which is likely attributable to the increased albedo and the formation of a layer of air owing to the elevated salt crust. Therefore, we suggest that the upward growth of salt precipitation should be comprehensively studied because it can cause significant reductions in evaporation rates and soil temperature.

Clouds and Vegetation Modulate Shallow Groundwater Table Depth

AbstractA 10-yr simulation of shallow groundwater table (GWT) depth over a temperate region in northwestern Europe, using a physics-based integrated hydrological model at kilometer scale, exhibits a strong seasonal cycle. This is also well captured in terms of near-surface soil moisture anomalies, terrestrial water storage anomalies, and shallow GWT depth anomalies from observations over the region. The modeled monthly anomaly of GWT depth exhibits a statistically significant (p &lt; 0.05) moderate positive/negative correlation with non-rain- and rain-affected monthly anomalies of incoming solar radiation. The vegetation cover also produces a strong local control on the variability of shallow GWT depth. Thus, much of the variability in the simulated seasonal cycle of shallow GWT depth could be linked to the distribution of clouds and vegetation. The spatiotemporal distribution of clouds, partly influenced by the Rhine Massif, modulates the seasonal variability of incoming solar radiation and precipitation over the region. Particularly, the southwestern and northern part of the Rhine Massif divided by the Rhine Valley exhibits a dipole behavior with relatively high (low) shallow GWT depth fluctuations, associated with positive (negative) anomaly of incoming solar radiation and negative (positive) anomaly of precipitation.

Soil Enzyme Activity as Affected by Land-Use, Salinity, and Groundwater Fluctuations in Wetland Soils of the Prairie Pothole Region

Land-use change and climatic variability are significant drivers for the loss of ecosystem services and soil quality in the prairie pothole region (PPR) wetland systems. Land-use induced changes in groundwater table and salinity may influence biogeochemical processes facilitated by extracellular enzymes (EEs) involved in soil organic matter (SOM) decomposition. The effects of changing groundwater table and salinity on β-glucosidase (BG), N-acetyl glucosaminidase (NAG), and alkaline phosphatase (AP) activities were assessed in wetland soils collected from three different adjacent riparian land-use practices in the PPR. In a microcosm study conducted over ten weeks, soils were treated with groundwater salinity (control, 6 mS cm−1, and 12 mS cm−1) and declining groundwater table depths. Extracellular enzyme activities (EEAs) differed significantly (p < 0.05) among soils from different land-uses and between groundwater table depths. The impact of groundwater salinity on soil EEAs were non-significant (p > 0.05). Soil EEAs were significantly higher in soils from pasture, suggesting that the land-use effects resulted from background SOC and TN. Soil EEAs significantly (p < 0.05) reduced under a deeper groundwater table depth, except reverse for BG in site B, indicated that the lowered groundwater table could lead to transitory drought stress for SOM decomposers.Graphical Abstract

Modelling the hydrological interactions between a fissured granite aquifer and a valley mire in the Massif Central, France

Abstract. We developed a high-resolution MIKE SHE/MIKE 11 model of a 231.3 ha headwater catchment in the granitic uplands of the French Massif Central to estimate the contribution of groundwater upwelling to the water balance of the Dauges mire, an acidic valley mire of international importance for nature conservation. We estimated that groundwater upwelling from the underlying weathered granite formations – mostly an approximately 55 m deep fissured zone – provides 27.1 % of total long-term inflows to the mire. This contribution increases to 37.2 % in September when total inflows are small. Overland boundary inflow accounts for an average of 40.2 % of total inflows. However, most of this originates from groundwater seepage through mineral soils along the mire margins or in small non-channelised valleys upslope of the mire. A sensitivity analysis showed that model performance in terms of the simulation of mire groundwater levels was most sensitive to parameters describing the mineral soils and weathered granite formations rather than the overlying peat layer. Variation partitioning demonstrated that groundwater upwelling was the most important factor driving simulated monthly groundwater table depth within the mire. Sustained groundwater upwelling maintains the mire water table close to or at ground level for most of the year. As a result, precipitation and overland boundary inflows quickly leave the wetland as saturation-excess runoff. There was close agreement between the observed distribution of mire habitats and areas where the simulated long-term groundwater seepage rate was larger than zero in September. Our results demonstrate that, contrary to the assumed small contribution of groundwater to the hydrology of hard-rock regions, groundwater upwelling from underlying weathered formations can be a quantitatively important and functionally critical element of the water balance of valley mires in granitic headwater catchments. These results have important legal and management implications.

Assessing the impacts of irrigated agriculture on hydrological regimes in an oasis-desert system

Irrigated agriculture greatly affects the hydrological systems and thereby eco-environment and food security in arid and semi-arid regions. However, a comprehensive assessment of the hydrological system dynamics in response to irrigated agriculture is still scarce, especially in oasis-desert systems of arid inland regions. Thus, we investigated the impact of irrigated agriculture on hydrological regimes in an oasis-desert system of northwest China. Temporal variations in water balance and lateral groundwater flow in oasis and desert experimental fields (i.e. oasis plot and desert plot) were quantified using the water balance analysis method. Soil water variations, groundwater dynamics and surface water and groundwater interactions in the oasis-desert system were determined by combining line transect survey methods and stable isotope (18O, 2H) techniques using the USGS MODFLOW software. The results showed that water exchange fluxes and groundwater dynamics were altered by the application of water-saving irrigation techniques and the increase in total precipitation. In particular, the downward total exchanging flux above groundwater table and the outward total lateral groundwater flow reduced significantly in the oasis plot. Spatial heterogeneity and profile variability of soil moisture along the soil water content (SWC) transect significantly reduced. Simultaneously, the depth dependence of SWC in oasis cropland and the deep soil moisture at the edge of desert were improved under water-saving irrigation scenario. Temporal variations in groundwater table depths (GTDs) exhibited three different patterns (i.e. stable, metastable and fluctuating) and maintained a continuously downward trend except for the oasis-desert ecotone along the GTD transect, and an abrupt change was found to have occurred during 2006–2012, prompting changes in the seasonality of groundwater resource availability. Groundwater recharge and discharge processes changed dramatically due to large-scale land reclamation and groundwater pumping. Groundwater depletion is approaching hydrological limits although the process is largely compensated by precipitation and streamflow variability. Water-saving irrigation in conjunction with restriction of land reclamation and adaptation of water management practices is, at least for the present, the most effective way to maintain the coexistence of oasis and desert ecosystems in arid inland regions.

Fuzzy-based multiple decision method for landslide susceptibility and hazard assessment: A case study of Tabriz, Iran

Due to the complexity of the causes of the sliding mass instabilities, landslide susceptibility and hazard evaluation are difficult, but they can be more carefully considered and regionally evaluated by using new programming technologies to minimize the hazard. This study aims to evaluate the landslide hazard zonation in the Tabriz region, Iran. A fuzzy logic-based multi-criteria decision-making method was proposed for susceptibility analysis and preparing the hazard zonation maps implemented in MATLAB programming language and Geographic Information System (GIS) environment. In this study, five main factors have been identified as triggering including climate (i.e., precipitation, temperature), geomorphology (i.e., slope gradient, slope aspect, land cover), tectonic and seismic parameters (i.e., tectonic lineament congestion, distribution of earthquakes, the unsafe radius of main faults, seismicity), geological and hydrological conditions (i.e., drainage patterns, hydraulic gradient, groundwater table depth, weathered geo-materials), and human activities (i.e., distance to roads, distance to the municipal areas) in the study area. The results of analyses are presented as a landslide hazard map which is classified into 5 different sensitive categories (i.e., insignificant to very high potential). Then, landslide susceptibility maps were prepared for the Tabriz region, which is categorized in a high-sensitive area located in the northern parts of the area. Based on these maps, the Bozgoosh-Sahand mountainous belt, Misho-Miro Mountains and western highlands of Jolfa have been delineated as risk-able zones.

Groundwater table monitoring and analysis of optimum groundwater table depth for crops in 1.6 million km&lt;sup&gt;2&lt;/sup&gt; of major grain-producing regions in China

Grain is the only source for the survival of humans and also serves as the foundation for social prosperity and stability. In China, 1.4 billion people are supported by 1.2 million km² of arable land. In this case, Chinese hydrogeologists make every effort to satisfy agricultural water needs, contributing substantially to the stable development of agriculture. This paper focuses on the functions of the 58 functional areas for agricultural product supply in the seven major grain-producing regions in China determined according geography, environment, and hydrologic conditions, as well as the construction of the National Groundwater Monitoring Project implemented by the Ministry of Natural Resources (also referred to as the Project) that cover 47 functional areas. Moreover, this paper makes the statistics of the data of 3177 monitoring points in the major grain-producing regions in China in 2020, obtaining the following results. Different crops have different optimum groundwater tables. For instance, the optimum groundwater table for wheat, soybean, and maize is 0.6‒1.5 m, 0.4‒1.0 m, and 0.4‒1.0 m, respectively in the case of loam soil and is 0.4‒1.5 m, 0.6‒1.5 m, and 1.5‒2 m, respectively in the case of sandy loam soil in the Huang-Huai-Hai Plain. For the 47 functional areas for agricultural product supply in China with a high density of groundwater monitoring points, the average annual groundwater tables were all lower than the lower limits of the optimum groundwater table depth ranges for crops in 2020, with the groundwater table depths occasionally higher than the lower limits in only seven of the functional areas throughout 2020. These data will contribute to high and stable crop yields, basic grain supply, and the elimination of extreme poverty.