Deep Groundwater Table Research Articles

Megacity solid waste disposal suitability mapping in Dhaka, Bangladesh: an integrated approach using remote sensing, GIS and statistics.

Selecting suitable Megacity Solid Waste Disposal (MSWD) sites is a challenging task in densely populated deltas of developing countries, exacerbated by limited public awareness about waste management. One of the major environmental concerns in Dhaka City, the world's densest megacity, is the presence of dumps close to surface water bodies resources. This study employed the Geographic Information System (GIS)-Analytic Hierarchy Process (AHP) framework to integrate geomorphological (slope and flow accumulation), geological (lithological and lineament), hydrogeological (depth to groundwater table and surface waterbody), socioeconomic (Land use land cover, distance to settlement, road, and airport), and climatological (wind direction) determinants, coupled by land-use and hydro-environmental analyses, to map optimal dumps (MSWDO) sites. The resulting preliminary (MSWDP) map revealed 15 potential landfill areas, covering approximately 5237 hectares (ha). Combining statistical analysis of restricted areas (settlements, water bodies, land use) with AHP-based ratings, the MSWDO map revealed two optimal locations (2285ha). Additionally, the hydro-environmental analysis confirmed the unsuitability of northern sites due to shallow groundwater (< 5.43m) and thin clay, leaving 11 options excluded. Sites 12 (Zone A, 2255ha) and 15 (Zone B, 30ha), with deeper groundwater tables and thicker clay layers, emerged as optimal choices for minimizing environmental risks and ensuring effective long-term waste disposal. This study successfully integrates remote sensing, geospatial data, and GIS-AHP modeling to facilitate the development of sustainable landfill strategies in similar South Asian delta megacities. Such an approach provides valuable insights for policymakers to implement cost-effective and sustainable waste management plans, potentially minimizing the environmental risks to achieve Sustainable Development Goals (SDGs) 6, 11, 13, and 15.

Shallow Groundwater Around Plateau Lakes： Spatiotemporal Distributions of Dissolved Carbon and Its Driving Factors

Dissolved carbon in groundwater plays an important role in carbon cycling and ecological function maintenance, and its concentration level affects the migration and transformation of pollutants in groundwater. To understand the spatiotemporal variation characteristics of dissolved carbon and its driving factors in shallow groundwater around plateau lakes, variations in the concentrations of dissolved organic carbon （DOC）, inorganic carbon （DIC）, and total carbon （DTC） and their driving factors in shallow groundwater （n = 404） around eight plateau lakes were analyzed. The results indicated that the average values of ρ（DOC）, ρ（DIC）, and ρ（DTC） in shallow groundwater around plateau lakes were 8.23, 49.01, and 57.84 mg·L-1, respectively, with the ρ（DOC） in 79.0% of shallow groundwater samples exceeding 5 mg·L-1. There were no significant differences in the DOC, DIC, and DTC concentrations between rainy and dry seasons, whereas the change in dissolved carbon concentrations in shallow groundwater were strongly affected by the intensity of agricultural intensification and the depth of groundwater table； the DOC, DIC, and DTC concentrations in shallow groundwater from facility agricultural regions （SFAR）, cropland fallow agricultural regions （CFAR）, and intensive agricultural regions with deeper groundwater tables （DIAR） were significantly reduced by 25.8% - 56.6%, 14.0% - 32.9%, and 16.6% - 36.7%, respectively, compared with those in intensive agricultural regions with shallower groundwater tables （SIAR）. Additionally, the dissolved carbon concentrations in shallow groundwater from DIAR were significantly lower than those of SFAR and CFAR. RDA revealed that physicochemical factors in water and soil significantly explained the changes in the dissolved carbon concentrations. Moreover, the dissolved carbon concentrations in shallow groundwater around Yilong Lake were significantly higher than those of other lakes, whereas that of Chenghai Lake was significantly lower than that of other lakes. Our study highlights that agricultural intensification intensity and groundwater table depth jointly drove the variations in dissolved carbon concentrations in shallow groundwater around plateau lakes. The study results are expected to provide a scientific basis for understanding the carbon cycle in plateau lake areas with underground runoff flowing into lakes and evaluating the attenuation of pollutants by dissolved carbon in shallow groundwater.

Numerical modeling of PFAS movement through the vadose zone: Influence of plant water uptake and soil organic carbon distribution

In this study, we investigated the effects of soil organic carbon (SOC) distribution and water uptake by plant roots on PFAS movement in the vadose zone with a deep groundwater table under temperate, humid climate conditions. Two series of numerical simulations were performed with the HYDRUS computer code, representing the leaching of historical PFOS contamination and the infiltration of water contaminated with PFOA, respectively. We considered soil profiles with three distributions of SOC (no SOC, realistic SOC distribution decreasing with depth, and uniform SOC equal to the content measured in topsoil), three root distributions (bare soil, grassland, and forest), and three soil textures (sand, sandy loam, and loam). The SOC distribution had a profound impact on the velocity of PFOS movement. The apparent retardation factor for realistic SOC distribution was twice as large as for the scenario with no SOC and more than three times smaller than for the scenario with uniformly high SOC content. We also showed that the root distribution in soil profoundly impacts the simulations of PFAS migration through soil. Including the root zone significantly slows down the movement of PFAS, primarily due to increased evapotranspiration and reduced downward water flux. Another effect of water uptake by plant roots is an increase of PFAS concentrations in soil water (evapo-concentration). The evapo-concentration and the slowdown of PFAS movement due to root water uptake are more significant in fine-textured soils than in sand.

Groundwater level influence on liquefaction potential at Pombewe housing site, Sigi regency, Central Sulawesi

The September 28, 2018, earthquake in Palu, Central Sulawesi, caused liquefaction and destroyed at least 3,720 houses. Therefore, it is necessary to consider the potential of liquefaction in choosing a residential location, especially in liquefaction-prone zones. The parameters of soil type, seismicity, and the groundwater table as a determinant of the saturation level determine liquefaction potential. The research aims to see the influence of groundwater level parameters in increasing the liquefaction potential when other parameters are met. The study was conducted at the Pombewe permanent housing site, Sigi Regency, Central Sulawesi. This shelter is an official relocation area for victims of the 2018 earthquake. Preliminary data stated that the location is safe from liquefaction potential because it has a deep groundwater table. The study used the CPT-based liquefaction triggering procedure method by Boulanger and Idriss and assumed that the groundwater table at the site was shallow. The Liquefaction Potential Index determines the potential liquefaction level. The results show that the area under review will only experience liquefaction if the groundwater table is above 1.0-11.6 meters (LPI&gt;0). If the water table rises above that depth, the LPI value increases to 1.6x10-9 – 0.44. Thus, the water table is a determining parameter in analyzing the liquefaction potential of an area.

Rainwater Harvesting through Point Recharge Method for Efficient Recharge of Tube Wells for Sustainable Management of Groundwater Resources in Karnataka

Water is a precious natural resource for sustaining life, agriculture and environment. The dependability on groundwater has reached high in all time in recent decades due to reasons such as unreliable supplies from surface water due to vagaries of monsoon, increase in demand for domestic, agricultural and other purposes. Karnataka is largely dependent on groundwater to meet industrial, municipal, domestic and irrigation needs. So, Rainwater harvesting (RWH) forms an important component for development and management of water resources for domestic, agricultural, municipal and industrial uses. Management of scanty rain fall by rain water harvesting, Augmentation of depleting natural resources of water (deeper ground water table) and Management of poor-quality ground water and scope for conjunctive/domestic use is need of the hour. With increase in withdrawal of ground water, ground water (GW) table is declining at a rapid pace with an urgent need to recharge GW in addition to dilute poor quality ground water. Double ring technique of Groundwater Recharge consists of filtering the water at different layers using gradation materials generally the pebbles of different size with synthetic material wrapped around the casing pipe. By harvesting rain water and recharging into point recharge soaking infiltration gallery established at Irrigation Water Management Research Centre, (IWMRC) Belavatagi Tq: Navalagund has shown encouraging results as far as water quality, discharge and water table are concerned. The results of assessment of influence of ground water recharge through rainwater harvesting on ground water yield (lps), quality (dS/m) and fluctuations (feet bgl) during the year 2020, have shown that around 3.35 lakhs liters of water could be collected from rain water harvesting during the year 2020. Also, from point recharge through 7 recharge events (rain fall events from July to October 2020), it was observed that the considerable rise in the water table from more than 100 feet below ground level to around 22 feet below ground level, drastic reduction in groundwater salinity i.e. electrical conductivity (EC) of ground water from more than 10 dS/m to an average (EC) of 1.32 dS/m and tube well yield has significantly increased from 0.4 lps to around 2.4 lps. Therefore, Artificial recharge techniques through rainwater harvesting can be a better strategic approach to combat the emerging problems of water scarcity especially over exploitation of ground water and its quality deterioration.

Simulation and Prediction of Groundwater Dynamics in Nagarjuna Sagar Right Canal (NSRC) Command for Normal and Extreme Groundwater Recharge Conditions

Groundwater Modeling is the best tool to optimize the different combinations and to select the best combination for sustainable groundwater management. Using computer models, best solution or scenario can optimize by creating model with real conditions. In this study, computer model Visual MODFLOW was applied to Nagarjuna Sagar Right Canal Command area to simulate the groundwater dynamics. The net area irrigated under Nagarjuna Sagar Right Canal is 4.75 lakh ha. The aquifer properties of various layers and boundary conditions were fed in to the model as input for calibration and validation of the model. After calibration and validation, the model was used to predict the groundwater dynamics in the study area using different recharge scenarios. The validated groundwater model was used to predict the groundwater levels in the study area for the years 2020, 2030 and 2040 with different recharge scenarios. Global climate model was used to generate future weather data. MarkSim developed by the International Centre for Tropical Agriculture (CIAT) was used to generate the weather parameters like maximum and minimum temperatures for the years 2020, 2030 and 2040. The different recharge scenarios with average, lowest and highest recharge over the study period and projected evapotranspiration have been used and revealed that the groundwater levels increase with the increase in recharge and decreases with the decrease in recharge. The results revealed that the groundwater depleted area would decrease with the highest recharge scenario and it would increase with the lowest recharge scenario in future. The deeper groundwater table would be expected in future at Chimakurthy and Thalluru villages of Prakasam district and Karempudi and Piduguralla villages of Guntur district in the study area. This condition may be due to the excess utilization of groundwater which is less than the groundwater recharge in particular villages. The construction of rainwater harvesting structures for artificial groundwater recharge in those areas should be carried out immediately.

Parametric Analysis of Rainfall-Induced Loess Soil Slope Due to the Rainwater Infiltration

Hydraulic properties (such as soil–water characteristic curves (SWCC) and hydraulic conductivity function (HCF)) play an important role in evaluating the stability of unsaturated soil slopes. Loess soils are widely distributed in Gansu Province in China, and most of them are in unsaturated conditions due to the deep groundwater table (G.W.T). In this study, twenty-eight sets of data published in the literature were analyzed to develop the upper and lower bounds of the SWCC for loess soil in Gansu. The variation of HCF for the loess soil was estimated from the upper and lower bounds curve developed in this study. Subsequently, numerical analyses incorporating scenarios considering different SWCCs, HCFs, and rainfall conditions were conducted for investigating the effects of those factors on the rainfall-induced slope stability. The results of analyses indicate that the infiltration plays an important role in the rainfall-induced slope stability. Higher permeable soil leads to a larger infiltration amount, which, in turn, results in a lower safety factor. In addition, the effect of the hydraulic property on the rainfall-induced slope stability decreases with the increase in slope angle.

Responses of soil respiration to simulated groundwater table and salinity fluctuations in tidal freshwater, brackish and salt marshes

Hydrological and salinity fluctuations in coastal wetlands induced by climatic change (e.g., drought) and anthropogenic activities can significantly affect the blue carbon sink via soil respiration (CO2 emissions). However, little information is available on the interactive effects of the groundwater table and salinity on soil respiration in coastal wetlands. Here, in situ soil columns were collected from tidal freshwater wetlands, brackish wetlands, and salt marshes to conduct a simulated assessment of the effects of fluctuations in the groundwater table (−30 cm, −20 cm and −10 cm) and salinity (0 ppt, 12ppt, and 26 ppt) on soil respiration in the field. The results showed that soil respiration in tidal freshwater wetlands (0.56–2.1 μmol/m2/s) and salt marshes (0.19–2.02 μmol/m2/s) was higher than that in brackish wetlands (0.17–0.9 μmol/m2/s) in all groundwater table and salinity treatments. The diurnal variation in soil respiration in the three simulated wetlands showed a unimodal curve, while the peak time was influenced by the groundwater table and salinity, with the maximum occurring at 11 a.m.-2 p.m. Soil respiration in tidal freshwater wetlands and brackish wetlands was significantly higher in the deep (−30 cm) and medium (−20 cm) groundwater table treatments than in the shallow (−10 cm) groundwater table treatment (p < 0.05) and significantly higher in the low (0 ppt) and medium (12ppt) salinity treatments than in the high (26 ppt) salinity treatment (p < 0.05). However, soil respiration in salt marshes decreased significantly as the groundwater table and salinity increased (p < 0.05). The groundwater table and salinity exhibited significant interactive effects on soil respiration in brackish wetlands (p < 0.05) and salt marshes (p < 0.01). Additionally, significantly negative correlations were observed between soil respiration and groundwater table and salinity in three wetlands (p < 0.05). Soil respiration in the three wetlands was significantly and positively correlated with microbial biomass carbon (p < 0.05) and significantly and positively correlated with soil organic carbon and total nitrogen (p < 0.01). The findings of this work can help reduce the uncertainty of model to accurately estimate carbon cycling of coastal wetlands at local, regional and global scales, and improve the blue carbon sink of coastal wetlands by regulating the groundwater table and salinity levels in wetland restoration projects.

Лесопригодность экотопов Волго-Ахтубинской поймы для культур сосны

In the south of European Russia, the largest sand massifs are found in the zone of dry steppes and semi-deserts. Effective utilization of such lands requires creation of protective forest planting of drought-resistant coniferous species like Scots pine and Crimean pine. The productivity and longevity of such stands vary widely over the territory and depends on the presence of additional to atmospheric precipitation water supply and the root layer mineral supply. In this regard, sand massifs of steppificated river valleys composed of multiphase or single-phase polymineral rocks are of particular interest for afforestation. One of the most important objects of afforestation is the Northern (within the Volgograd region) highest and most drained part of the Volga-Akhtuba floodplain. Volga River damming by the Volga Hydroelectric Station (Volga GES) led to a restructuring of surface and ground water regimes, formation of new conditions of water and mineral nutrition and changes in other important factors of forest ecosystems in the area. The research aims at developing a classification of the Volga-Akhtuba floodplain ecotopes by water-mineral nutrition conditions, cultivation, expected productivity and longevity of pine plantings. We studied relationships of growth parameters of Pinus silvestris L. stands with soil-ground and hydrological conditions in different ecotopes of the large hilly and transitional floodplains after the Volga River damming by the Volga GES. Dynamics patterns of this relationship were revealed. It was found that in the northern part of the Volga-Akhtuba valley (approximately up to the Kapustin Yar – Kamenny Yar line) with increasing stratification, heavier granulometric composition of the root layer to sandy loam layer, lowering the surface level at a small distance from the drainage channel moisture supply and growth of Scots pine plantations improve, forest suitability of ecotopes increases. There is a risk of early decay and death of high-density pine forests in periods of low water and dry years on soils underlain by thick loams. Three groups of ecotope forest suitability were identified according to these indicators, as well as the conditions for the creation of forest plantations, productivity and longevity of plantings. The least favorable ecotopes are in the highlands of the hilly and transitional floodplains with minor soils of different composition on single-phase open-textured sands with deep (more than 4–5 m) groundwater table during low-water season. The most favorable are welldrained areas of the transitional floodplain with light soils on thick stratified predominantly sandy loam sediments, as well as on sands with close to the surface groundwater occurrence. Average ecotopes in terms of conditions are poorly drained areas of the transitional floodplain with minor sandy loam and loamy soils on deep loams.

Estimating soil water flux from single-depth soil moisture data

• We introduce a new analytical relationship between soil moisture and water flux. • Flux can be calculated from single-depth moisture data along the unsaturated zone. • The new solution is based on Richards equation with arbitrary hydraulic functions. • This solution allows shallow or deep groundwater table at the bottom boundary. Finding a relationship between soil moisture and soil water flux at a single soil depth has been of particular interest in recent years. Such a relationship, however, is challenging to derive due to a high degree of nonlinearity of the soil water flow governing equation, known as Richards equation. This paper presents a new algebraic soil moisture-flux relationship based on an approximate analytical solution of Richards equation with arbitrary soil hydraulic functions. This solution accounts for the groundwater contributions to soil moisture variations along the unsaturated zone. The new solution was evaluated using numerical solutions of Richards equation via the HYDRUS-1D model. Despite its simplicity, the new solution could reproduce HYDRUS-1D simulations for a homogeneous soil profile with coefficient of determination (R 2 ) higher than 0.9 in most cases. The new solution offers a potential approach to modeling groundwater recharge in existing groundwater models. In particular, this model can potentially provide a more realistic recharge estimate compared to the kinematic-wave approximation of Richards equation, that neglects upward flows through the vadose zone. Future research is needed to account for soil layering and root water uptake in the soil moisture-flux relationship.

The Stem Sap Flow and Water Sources for Tamarix ramosissima in an Artificial Shelterbelt With a Deep Groundwater Table in Northwest China.

The shelterbelt forest between oases and the desert plays a vital role in preventing aeolian disasters and desertification in arid regions of northwest China. Tamarix ramosissima (T. ramosissima), a typical perennial and native xerophyte shrub in Northwest China, grows naturally and is widely used in building artificial shelterbelt forests. The balance between water consumption and the availability of water determines the survival and growth of T. ramosissima. How T. ramosissima copes with extremely low rainfall and a deep groundwater table remains unknown. To answer this, the transpiration and the water sources of T. ramosissima were investigated by the heat balance and oxygen isotopic analysis method, respectively. Our results show that the daily T. ramosissima stem sap flow (SSF) was positively correlated with air temperature (Ta), photosynthetically active radiation (PAR), and the vapor pressure deficit (VPD). We found no significant relationship between the daily SSF and soil moisture in shallow (0–40 cm) and middle (40–160 cm) soil layers. Oxygen isotope results showed that T. ramosissima mainly sources (>90%) water from deep soil moisture (160–400 cm) and groundwater (910 cm). Diurnally, T. ramosissima SSF showed a hysteresis response to variations in PAR, Ta, and VPD, which suggests that transpiration suffers increasingly from water stress with increasing PAR, Ta, and VPD. Our results indicate that PAR, Ta, and VPD are the dominant factors that control T. ramosissima SSF, not precipitation and shallow soil moisture. Deep soil water and groundwater are the primary sources for T. ramosissima in this extremely water-limited environment. These results provide information that is essential for proper water resource management during vegetation restoration and ecological reafforestation in water-limited regions.

Tracking and modelling water percolation process in modern intensive farming loess terraces

Loess slopes along the Yellow River in China are prone to failure in response to intensive irrigation. Existing studies found that the wetting front depth subjected to intensive farming water could barely reach 6 m in loess terrace. Long-term field monitoring revealed that irrigation water takes a short time to recharge the groundwater. Yet the dynamic process and mechanism of irrigation water percolation through thick unsaturated loess remains unrevealed. To address this problem, the Heifangtai terrace was selected as the study area and a series of unique full-scale controlled field irrigation experiments were carried out combined with numerical modelling. The variations in water content, pore-water pressure, and electrical resistivity over time were monitored. From the field testing, the unsaturated stratified loess layer could be divided into two vadose zones based on the water percolation characteristics, namely, transient flow zone (0–6.5 m) and steady flow zone (>6.5 m). Variation in water content presented a hysteresis effect in the transient flow zone compared with the steady flow zone. In the whole seepage process, the vertical percolation rate of 0.5 m/day was double that of the horizontal percolation rate. Furthermore, the irrigation water percolating process was modelled using a finite element code, PANDAS, which was validated by the field testing. Numerical simulation results demonstrated that the movement of wetting front was hampered by the air outflow within transient flow zone and that irrigation water reached the deep groundwater table through the thick unsaturated stratified loess within 100 days, which was consistent with the field monitoring data. This research aids in a better understanding of the irrigation water percolation process in unsaturated stratified loess in the loess region.

The effect of flow partition on storm runoff and pollutant retention through raingardens with and without subsurface drainage

Green infrastructures (GIs) have been advocated worldwide to mitigate the negative impact of urbanization on regional hydrological cycle, their functions are closely related to their design features and the local environmental condition. This paper reports a field monitoring study that aimed to investigate how runoff partition in raingardens would affect flow and pollutant retention. A paired field experiment was conducted to compare runoff and pollutant retentions in two raingardens with and without subsurface drainage in a shallow water table area. Concentrations of ammonia nitrogen (NH3–N), nitrate nitrogen (NO3–N) and total phosphorus (TP) were measured at raingarden inflow, overflow and drainage paths. The results from 28 monitored storm events over two years showed that the raingarden without subsurface drainage achieved its retention mainly through ponding and infiltration, its pollutant retention rates (76% for TP, 81% for NO3–N, and 79% for NH3–N) were higher than its runoff retention rate (61%), indicating a first flush effect on pollutants retention in the raingarden during storm events, especially when the raingarden was empty and dry. The raingarden with subsurface drainage facilitated quick discharge of water, the observed runoff reduction through the raingarden was 36%; pollutant removal rates were quite variable: NH3–N was removed by 91% while the NO3–N and TP were increased by 3–47%. These results suggest that facilitating specific processes for targeted pollutants is necessary for achieving substantial pollutant removal in a stormwater retention device. Subsurface drainage pipes resulted in short circulating of runoff and lowered pollutant removal rates in the raingarden. Considering the water table fluctuation during the experimental period, we recommend to build infiltration-based GI devices to better capture first flush in intensively developed urban area, which caused deeper groundwater table. In conclusion, installations of different GI devices in urban landscape need to consider the local environmental conditions and facilitate the design features to meet specific storm runoff and pollutants mitigation requirement.

Field infiltration of artificial irrigation into thick loess

Frequent agricultural irrigation triggers numerous landslides in the loess platform, northwest China. We conducted a field infiltration experiment with a diameter of 20 m on the South Jingyang tableland in Shaanxi province, China to better understand the infiltration process in thick unsaturated loess. Soil moisture probes, tensiometers, and differential pressure transducers were installed at various depths to monitor the infiltration process. The results showed that the initially high infiltration rate gradually decreased and finally approached a constant value less than that of the saturated hydraulic conductivity of the top soil. Matric suction decreased rapidly, and the volumetric water content increased to a nearly saturated state with the arrival of the wetting front. The soil water characteristic curve obtained from field monitoring data agreed with that from laboratory tests performed on undisturbed specimens. Preferential flow associated with vertical cracks parallel to the margin of the platform was observed in the late Pleistocene Loess layer (L1), and an empirical model was developed from monitoring recordings to explain preferential flow formation. A transient perched water table formed above the lower part of the first paleosol layer (S1). The monitored pore-air pressure increased and then fluctuated before the arrival of the wetting front. The maximum value of pore-air pressure at different depths was less than 5 kPa and tended to increase linearly with dry density. The results of this research help understand the migration of irrigation water in thick unsaturated loess and the recharge mechanism of the deep groundwater table.

Monitoring Drought through the Lens of Landsat: Drying of Rivers during the California Droughts

Water scarcity during severe droughts has profound hydrological and ecological impacts on rivers. However, the drying dynamics of river surface extent during droughts remains largely understudied. Satellite remote sensing enables surveys and analyses of rivers at fine spatial resolution by providing an alternative to in-situ observations. This study investigates the seasonal drying dynamics of river extent in California where severe droughts have been occurring more frequently in recent decades. Our methods combine the use of Landsat-based Global Surface Water (GSW) and global river bankful width databases. As an indirect comparison, we examine the monthly fractional river extent (FrcSA) in 2071 river reaches and its correlation with streamflow at co-located USGS gauges. We place the extreme 2012–2015 drought into a broader context of multi-decadal river extent history and illustrate the extraordinary change between during- and post-drought periods. In addition to river extent dynamics, we perform statistical analyses to relate FrcSA with the hydroclimatic variables obtained from the National Land Data Assimilation System (NLDAS) model simulation. Results show that Landsat provides consistent observation over 90% of area in rivers from March to October and is suitable for monitoring seasonal river drying in California. FrcSA reaches fair (&gt;0.5) correlation with streamflow except for dry and mountainous areas. During the 2012–2015 drought, 332 river reaches experienced their lowest annual mean FrcSA in the 34 years of Landsat history. At a monthly scale, FrcSA is better correlated with soil water in more humid areas. At a yearly scale, summer mean FrcSA is increasingly sensitive to winter precipitation in a drier climate; and the elasticity is also reduced with deeper ground water table. Overall, our study demonstrates the detectability of Landsat on the river surface extent in an arid region with complex terrain. River extent in catchments of deficient water storage is likely subject to higher percent drop in a future climate with longer, more frequent droughts.

Using intrinsic vulnerability and anthropogenic impacts to evaluate and compare groundwater risk potential at northwestern and western coastal aquifers of Sri Lanka through coupling DRASTIC and GIS approach

Groundwater vulnerability assessment has become a crucial step in successfully protecting groundwater against pollution. An attempt of this study has been made to evaluate groundwater contamination risk using intrinsic vulnerability and land-uses in Vanathavillu, Kalpitiya and Katana area in Sri Lanka, using coupled DRASTIC with GIS as feasible methodology. The findings reveal that the groundwater in the areas under study falls under very low to high contamination risk. The higher risk of contamination has been identified in most of the Kalpitiya (about 82%) with the moderate along the beach in the west and next to Puttalam lagoon in the northeast and southeast. This is mainly due to pollution risk inherent with intense vegetable cultivation, over pumping, shallow groundwater tables and permeable sandy soil. Vanathavillu is under very low to moderate contamination risk, in which the moderate risk (about 13%) has especially been found the center, central southwest and west of the area. The relative less deep groundwater tables, possible seepage from the underlying limestone aquifer and less permeable red earth soil could be cause for the moderate risk in the area. Furthermore, results show that the Katana has low to moderately high groundwater contamination risk. Nitrate has a good agreement with the different pollution risk classes and that nitrate can be used as an indicator of aquifer degradation inherent with land-use activities in the coastal areas. Groundwater quality monitoring network should be set up to minimize the anthropogenic acts, particularly in high and moderate contamination risk zones.

Variability of Bimodal Soil-Water Characteristic Curves under Different Confining Pressures

Soils with two subcurves of Soil-Water Characteristic Curve (SWCC) (dual porosity soils) might be found within various residual soils. Soils located in different depths have different confining pressure. Residual soils are found in the unsaturated zones due to the deep groundwater table. There is a linear correlation between the hydraulic properties of the soil in the unsaturated area and that of its unsaturated properties. This study aims to examine the influence of the confining pressure towards the SWCC of dual porosity soil. The scope of this study involves measurements of the drying and wetting SWCC using Tempe cells, pressure plates, and an advanced triaxial apparatus. In this study, the mathematical equations were developed to explain the effect of confining pressure on SWCC. The experimental results indicated that the dual porosity soil exhibits bimodal characteristics for the drying curve of SWCC and it exhibits unimodal characteristics for the wetting curve of SWCC. As the confining pressure increases, the air entry values, the inflection points, and the standard deviation of drying SWCC increase. In addition, the hysteresis of SWCC is becoming smaller with the increasing confining pressure.

Three-dimensional slope stability analysis incorporating unsaturated soil properties in Singapore

ABSTRACT Rainfall-induced slope failure is a natural hazard that occurs in many parts of the world. To identify areas where rainfall-induced slope failure may potentially occur in Singapore, a slope susceptibility map of needs to be developed. Majority of the slope failures occurred in residual soils during or after torrential rainfall. In Singapore, residual soils are generally unsaturated because of the deep groundwater table. Hence, it is important to incorporate unsaturated soil properties (i.e. soil–water characteristic curve) in the development of slope susceptibility map in Singapore. In this study, spatial distributions of saturated and unsaturated soil properties were estimated using ordinary kriging. Seepage analysis of zonation in the residual soil from Bukit Timah Granite was carried out using Transient Rainfall Infiltration and Grid-Based Regional Slope-Stability Model (TRIGRS), a publicly available software. The resulting pore-water pressures from the seepage analyses were incorporated into Scoops3D for three-dimensional slope stability analyses. Most areas in the investigated zone were found to have high factors of safety. Only 0.054% of the investigated zonation was associated with very low factors of safety.

Solid-liquid distribution coefficients (Kd-s) of geological deposits at the Chernobyl Nuclear Power Plant site with respect to Sr, Cs and Pu radionuclides: A short review.

A review is presented of data on solid-liquid distribution coefficients (Kd-s) of the main radiologically important radionuclides of the Chernobyl release within geological deposits at the Chernobyl Nuclear Power Plant (ChNPP) Site. The Kd values for Sr, Cs and Pu for Quaternary sandy deposits that form sedimentary cover at Chernobyl fall within the range of parameters reported in international sorption databases. In agreement with general knowledge on radionuclide geochemical behavior and affinity to soils, Kd-s increase in the sequence: Sr < Cs < Pu. Alluvial and fluvioglacial sandy deposits are characterized by larger Kd values then deposits of eolian genesis due to higher content of clay minerals in fine fractions. For Sr, laboratory batch tests have given Kd values that are in a reasonable agreement with in situ measurements. At the same time, the 90Sr Kd-s obtained from groundwater transport model calibrations were noticeably lower than experimentally determined values, thus showing potential limitations of the Kd-approach. Monitoring data on mobility of 90Sr, 137Cs and 239,240Pu in groundwater in the Chernobyl zone on a whole are consistent with the radionuclide Kd-s summarized in this article. The highest concentrations in groundwater (based on data for 2012-2014) were observed for 90Sr, while orders of magnitude lower concentrations were observed for 137Cs and 239,240Pu. At the same time, detection of 137Cs and 239,240Pu in groundwater at sites with a relatively deep groundwater table suggests the possibility of facilitated transport of small amounts of these radionuclides in the form of non-retarded colloids or complexes.

Effects of soil texture and groundwater level on leaching of salt from saline fields in Kesem irrigation scheme, Ethiopia

In Ethiopia, soil salinity has become a challenge for agricultural production in irrigated arid and semi-arid areas. This research investigates the effectiveness of leaching salt remediation under different soil textures and groundwater tables. Leaching was conducted in the bare parts of three abandoned saline fields. Soil texture of Field 1 (F1) is sandy loam while Field 2 (F2) and Field 3 (F3) are clay loam. The F1, F2, and F3 groundwater was located at 1.8, 1.5 and &amp;gt; 3 m, respectively. The leaching requirement water levels were 15, 20, 25, and 30% higher than the evaporation of the bare field needed for four consecutive weeks, respectively. The results of this study show that, after four days of leaching, the salinity of F1 with sandy loam texture was significantly (P &amp;lt; 0.05) and more strongly reduced than for the other fields exhibiting clay loam texture. For F1, salinity was reduced from 16.3 to 6.2 dS/m and from 12.4 to 5.5 dS/m at depths of 0–30 and 30–60 cm, respectively. In head parts of F1 and F3, the salinity level was reduced to 2.0 dS/m. However, in F2 with shallow groundwater and clay loam texture, the salinity levels were slightly higher after leaching, i.e. from 11.2 to 12.0 dS/m and from 8.1 to 11.6 dS/m at 0–30 and 30–60 cm depths, respectively. In our experiment, effective leaching was achieved only in the field with sandy soil and deeper groundwater table. We saw that the application of leaching with surface drainage at shallow groundwater levels may further exacerbate salinity problems. For such situations, the use of subsurface drainage could sustain the groundwater depth and prevent additional salinization. On clay-textured fields with shallow groundwater table, a prolonged leaching application is necessary to reduce the salt contents.