Groundwater Level Changes Research Articles

ANALYSIS OF CHANGES IN GROUNDWATER LEVELS IN QUATERNARY DEPOSITS IN THE SOUTH-EASTERN PART OF THE IRTYSH-OB ARTESIAN BASIN

Link for citation: Balobanenko A.A., Vasilyev D.I., Dutova E.M., Kuzevanov K.I. Analysis of changes in groundwater levels in quaternary deposits in the south-eastern part of the Irtysh-Ob artesian basin. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 7, рр. 202-213. In Rus. Relevance. The tasks of studying the level regime of groundwater are very closely related to the need to predict their resources under the influence of both natural and artificial factors in order to develop scientific foundations for the rational use of water resources and effective management of the groundwater regime in the study area. Purpose: to study changes in the level regime of groundwater for domestic and drinking purposes in Quaternary deposits in the south of the West Siberian artesian basin based on the results of long-term regime observations. Objects: groundwater of the Irtysh-Ob artesian basin of the II order, the southeastern part of the West Siberian artesian basin of the I order, most actively involved in the sphere of anthropogenic activity. The study area is confined to a province with stable seasonal freezing of the aeration zone, where the main groundwater recharge is carried out in the spring due to snowmelt. Methods. The methodology for conducting observations of groundwater levels was determined by the regulations of the former USSR Ministry of Geology, and then the Ministry of Natural Resources of the Russian Federation, this paper presents a statistical processing of time series of observations of groundwater levels and a comparison of the results obtained with the data on the water regime of surface watercourses and climatic characteristics of the study areas. Results. The leading influence of climatic conditions on the main regularities of the natural hydrodynamic regime of groundwater was revealed. A different degree of intensity of the influence of external factors is shown, expressed by the amplitude of the groundwater level, depending on the type of groundwater regime and the degree of moistening of the territory. Natural factors have the least effect on groundwater as they move away from draining ones and with increasing depth.

Groundwater monitoring and specific yield estimation using time-lapse electrical resistivity imaging and machine learning

This paper presents an alternative method for monitoring groundwater levels and estimating specific yields of an unconfined aquifer under different seasonal conditions. The approach employs the Time-Lapse Electrical Resistivity Imaging (TL-ERI) method and machine learning-based time series clustering. A TL-ERI survey was conducted at ten sites (WS01-WS10 sites) throughout the dry and wet seasons, with five-time measurements collected for each site, in the Taichung-Nantou Basin along the Wu River, Central Taiwan. The obtained resistivity raw data was inverted and converted into normalized water content values using Archie’s law, followed by applying the Van Genuchten (VG) model for the Soil Water Characteristic Curve to estimate the Groundwater Level (GWL), and estimated the theoretical specific yield (Sy) by computing the difference between the saturated and residual water contents of the fitted VG model. In addition, the specific yield capacity (Sc), representing the nature of the storage capacity in the aquifer, was also calculated. The results showed that this approach was able to estimate those hydrogeological parameters. The spatial distribution of the GWL reveals that during the dry-wet seasons from February to July, there was a high GWL that extended from southeast to northwest. Conversely, during the wet-dry seasons from July to October, the high GWL shrank, which can be attributed to recharge variations from rainfall events. The determined spatial distribution of Sy and Sc fall within the range of 0.03–0.24 and 0.14–0.25, respectively. To quantitatively establish areas of similar groundwater level changes along with the VG model parameter variations during the study period, a Time series Clustering analysis (TSC) was performed by utilizing Hierarchical Agglomerative Clustering (HAC). The findings suggest that the WS03 site is a promising area for further investigation due to its highest Sc value with a slight change in groundwater levels during the dry and wet seasons. This study brings an advanced development of the geoelectrical method to estimate regional hydrogeological parameters in an area with limited available groundwater observation wells, in different seasonal conditions for groundwater management purposes.

Dynamic variation of groundwater level and its influencing factors in typical oasis irrigated areas in Northwest China

Abstract It is essential to analyze the dynamic characteristics of regional groundwater levels and their driving factors for the rational development of groundwater in irrigated areas. This article explores the spatial distribution characteristics of the amplitude of groundwater level change in the Shihezi irrigated area by using the ArcGIS interpolation method and contrast coefficient variance method and analyzes the influence factors of dynamic change of groundwater levels by integrating the grey relational degree and path analysis methods and obtaining the sensitivity of each influencing factor to changes in groundwater levels and the relative importance of the influencing factors. The following results are obtained: (1) the groundwater level of the Shihezi irrigated area showed an overall increasing trend from 2012 to 2019, with a fluctuation range of 12.26–14.14 m. The groundwater level in the southeast of the irrigated area showed an upward trend, while the groundwater level in the northwest area showed a downward trend. (2) The groundwater level in the irrigated area first increased, then decreased, and then increased again. The variance of the contrast coefficient in the irrigated area ranged from 0.04 to 11.31, and the fluctuation range of the groundwater level in the central area was higher than that in the northern and southern areas. (3) The irrigated area of cultivated land and evaporation are the main factors affecting groundwater level change in the Shihezi irrigated area. The grey relation analysis shows that the irrigated area of cultivated land has the highest grey correlation degree with the evolution of the groundwater level, which is 0.947, and the average grey correlation index is between 0.74 and 0.95. Path analysis showed that the irrigated area of cultivated land, surface water usage, and evaporation were the main factors affecting groundwater levels. Human activities are one of the main driving forces of groundwater level change, and the research results provide a theoretical basis for the rational utilization and sustainable development of groundwater resources in the Shihezi irrigation area.

Assessment of Spatial Variability of Groundwater Levels in Moroto District, Uganda

Globally, the variation of groundwater levels is increasingly overwhelming due to over exploitation resulting from population growth. The dynamic nature of socio-economic activities in Moroto District such as agriculture, settlements and increased trends in irrigation technology has been well-known worldwide as common parameters triggering groundwater variability. Nevertheless, determination of groundwater levels for groundwater management and development purpose is a challenge due to spatial variability in levels across Moroto District. In this study, geostatistical technique in Geographical Information System (GIS) was used to analyze spatial variability of water levels in the study area. The analysis utilized ordinary Kriging method to predict the spatial variation of groundwater levels for 189 measured boreholes. The resultant groundwater level variation map generated using Gaussian model depicts change in groundwater levels varying significantly across the study area dropping by 12 m to 50 m. Significant variations of groundwater levels were observed in the western, central and south eastern part of the study area which are highly populated areas and therefore, the potential of overexploitation. Generated map can be used as first-hand information for decision makers and water managers in management of groundwater resources in Moroto District.

Changes in widespread aquifer properties caused by a magnitude 6-class earthquake evaluated using InSAR analyses

Correlations between surface displacements and groundwater level changes have been widely used to understand aquifer properties and their site characteristics; however, the underlying mechanisms of various correlation types and the influence of earthquakes have not been fully investigated. In this study, we examine correlations between surface displacements from interferometric synthetic aperture radar analyses and groundwater level monitoring data in Osaka and Kyoto, Japan, over 4 years, a period including the 18 June 2018 Mw 5.6 northern Osaka earthquake. Both positive and negative correlations between the seasonal groundwater level changes and the seasonal surface displacements are identified. Based on the observations of the effects of the earthquake, a new conceptual aquifer dynamical model driving the relationship between the surface displacements and the groundwater level changes is proposed. We further reveal that sites with negative correlations increased after the earthquake, suggesting that the earthquake increased the groundwater recharge rate as a result of increases in aquifer transportation properties such as permeability and porosity.

Understanding the Spatiotemporal Characteristics of Land Subsidence and Rebound in the Lianjiang Plain Using Time-Series InSAR with Dual-Track Sentinel-1 Data

The Lianjiang Plain, renowned for its position as ‘China’s textile hub’ and characterized by its high population density, has experienced considerable subsidence due to excessive groundwater extraction in recent years. Although some studies have investigated short-term subsidence in this plain, research on long-term subsidence and rebound remain understudied. In this paper, the characteristics of surface deformation in the Lijiang Plain during two periods (2015–2017 and 2018–2021) have been investigated using the time-series interferometric synthetic aperture radar (TS-InSAR) technique, and the correlation with the changes in groundwater level, geological factors, and urban construction are discussed. The InSAR-derived results are cross-validated with the adjacent orbit datasets. Large-scale and uneven subsidence ranging from −124 mm/year to +40 mm/year is observed from 2015 to 2017. However, a significant decrease in the subsidence rate during 2018–2021, with local rebound deformation up to +48 mm/year in three regions, is also observed. Groundwater level changes are found to be the major cause of the ground deformation, and the intercomparison between groundwater level and ground displacement time series from TS-InSAR measurements also indicates a clear relationship between them during 2018–2021. Geological factors control the range of deformation area over the study period. The impact of urban construction on surface subsidence is evident, contributing to high deformation. Our findings could improve the understanding of how deformation is affected by groundwater rebound and offer valuable insights into groundwater management, urban planning, and land subsidence mitigation.

Monitoring of the mining waste neutralization facility of LW Bogdanka

Investing in renewable energy sources bringing direct profits from unattractive areas is one of the most advantageous ways of wastelands revitalization. In the case of post-mining dumps, it is realized by using photovoltaics and wind turbines. Analyzes showed that the greatest benefits can be acquired from photovoltaic farms, mainly due to the simplicity of their design and principles of operation, as well as the quick return on investment - up to 7 years. The construction of wind turbines is more complicated. Despite the favorable conditions of the mining dumps (elevated areas, which are located mainly away from residential buildings), the construction of the turbine requires more effort in designing and installation work, mainly due to the necessity of building the foundations. Methods for revitalizing mine dumps by installing renewable energy systems have some limitations due to periodicity of operation (time of day, season), weather conditions (wind speed, temperature), expensive energy storage, etc. For this reason, real-time monitoring of climatic conditions is required. The following parameters are monitored: the average available solar energy (important for the assessment of the efficiency of photovoltaic cells), speed and direction of the wind (which affects the efficiency of wind turbines), changes in groundwater level (risk of flooding and periodic soil softening), soil and air temperature (air – affects the choice of the method of revitalization, soil – affects the preservation of soil) and dust concentration, which affects the degree of contamination of the photovoltaic modules and thus the efficiency of the photovoltaic (PV) power plant. The presentation includes interesting data that was obtained during the tests.

A Spatiotemporal Characterization of Water Resource Conditions and Demands as Influenced by the Hydrogeologic Framework of the Willcox Groundwater Basin, Southeastern Arizona, USA

In the Willcox Groundwater Basin (WGB), increasing rates of agricultural groundwater withdrawal have led to significant regional groundwater level decline, threatening the basin’s long-term water resource security. Updated characterization of the basin’s water resource conditions and agricultural water demand is critically important for informing groundwater resource management efforts. We developed the hydrogeologic framework of the WGB and linked groundwater level data with land cover classification data to provide a spatiotemporal assessment of water resource conditions and agricultural development in the WGB. A correlation analysis evaluated the degree of association between the basin’s mean annual depth-to-groundwater and agricultural land cover extent. Results of this study indicate that between 2008 and 2021, agricultural land cover in the WGB increased by 29%. The average rate of groundwater level change in the basin’s measured wells was calculated at −13.8 m between 2006 and 2021. We found a strong correlation between the basin’s mean annual measured depth-to-groundwater and the annual agricultural land cover extent, further reinforcing the understanding of agricultural water use in the basin as a principal driver of groundwater level decline. The methodological framework employed proved a simple and effective way to assess groundwater resources as influenced by geology and land use. The outcomes of this study provide critical information toward improved water resources management by providing an integrated understanding of local hydrogeology, groundwater level variability, and changes in agricultural land cover in arid inland basins such as those found in Arizona, USA.

Changes in groundwater levels across China from 2005 to 2016

Groundwater provides perennial, ubiquitous and high-quality freshwater supplies for humanity globally. Difficulties in the collection and collation of groundwater records have hindered our understanding of large-scale groundwater dynamics. This study collected groundwater level depth (GLD) records from 909 groundwater wells across China and the spatiotemporal changes in GLD were investigated in unconfined and confined aquifers from 2005 to 2016 nationally. The GLD distributions were highly heterogeneous, with average (standard deviation) GLDs of 11.9 (20.3) and 21.6 (26.4) m in unconfined and confined aquifers, respectively. From 2005 to 2016, the GLDs decreased significantly over the energy-limited region due to increased precipitation but increased significantly over the water-limited region due to high groundwater abstraction. The GLD changes in confined aquifers were larger than those in unconfined aquifers due to the smaller storativity in confined aquifers. The correlations between the GLDs and GRACE total water storage (TWS) anomalies over the water-limited region were higher than those over the energy-limited region, indicating that groundwater storage contributed more to TWS over arid areas than humid areas. This study highlights the increasing groundwater storage in the energy-limited region and the decreasing groundwater storage in the water-limited region, i.e., enhanced regional differences in groundwater resources. The results improve our understanding of groundwater dynamics in different aquifers and climatic conditions and hence advance robust groundwater management and policy development in China.

Climate change impact assessment on groundwater level changes: A study of hybrid model techniques

AbstractOne of the most important sources of water supply is groundwater. However, the groundwater level (GWL) is significantly impacted by the global climate change. Therefore, under these more severe climate change conditions, the accurate and simple forecast of farmland GWL is a crucial component of agricultural water management. A hybrid model (HM) of Bayesian random forest (BRF), Bayesian support vector machine (BSVM), and Bayesian artificial neural network (BANN) is built in this study. The HM is made up of a Bayesian model averaging (BMA) and three machine learning models: random forest (RF), support vector machine (SVM), and artificial neural network. These three HMs are employed to help automate logical inference and decision‐making in business intelligence for groundwater management. For this purpose, data on 8 separate climatic factors that impact GWL changes in the study area were acquired. Nine distinct farming communities' GWL change data were utilised as the dependent variables for each model fit (community data). The effectiveness of the HM techniques was assessed using the evaluation metrics of mean absolute error (MAE), coefficient of determination (R2), mean absolute percent error (MAPE), and root mean square error (RMSE). The model fit in Suhum had the greatest performance with the highest accuracy (R2 varied from 0.9051 to 0.9679) and the lowest error scores (RMSE ranged from 0.0653 to 0.0727, and MAE ranged from 0.0121 to 0.0541), according to the models' evaluation results. The BRF delivered the greatest results when compared to the two independent HMs, the BSVM and BANN. Future GWL and climatic variable data may be trained using the trained HM techniques to determine the effects of climate change. Farmers, businesses, and civil society organisations might benefit from continuous monitoring of GWL data and education on climate change to help control and prevent excessive deteriorations of global climate change on GWL.

MODELING OF GROUNDWATER LEVEL CHANGES DUE TO DEEP WELL EXTRACTION USING MODFLOW IN THE NORTH OF BANDAR LAMPUNG

The growth rate of urban areas in the north of Bandar Lampung has caused the extraction of groundwater resources through deep well pumping to increase. Therefore, it is necessary to study the impact of pumping to prevent groundwater depletion. This study performs numerical simulation modeling to identify the impact of deep well pumping on changes in groundwater levels in three sub-districts north of Bandar Lampung city. Modeling is done using MODFLOW-6 and ModelMuse as a graphical user interface (GUI). The simulation method uses steady-state and transient models with four stress periods in 2000, 2010, 2020, and 2030. A total of 30 data wells are used for model setup, and 15 of them as observation and validation points. The simulation results show that hydraulic head changes occur at depths of 10 m to more than 40 m. Drawdown and groundwater head changes are concentrated at deep well points with a radius of up to 1 km. The model also successfully identified a decrease in groundwater level to more than 8 m in the deepest well area DW1. Thus, it is necessary to take action that can overcome the impact of changes in groundwater level due to pumping from deep wells. Furthermore, groundwater storage engineering can be one solution by utilizing rainwater harvesting technology to recharge the groundwater aquifer system.

Converting Seasonal Measurements to Monthly Groundwater Levels through GRACE Data Fusion

Groundwater depletion occurs when the extraction exceeds its recharge and further impacts water resource management around the world, especially in developing countries. In India, most groundwater level observations are only available on a seasonal scale, i.e., January (late post-monsoon), May (pre-monsoon), August (monsoon), and November (early post-monsoon). The Gravity Recovery and Climate Experiment (GRACE) data are available to estimate the monthly variation in groundwater storage (GWS) by subtracting precipitation runoff, canopy water, soil moisture, and solid water (snow and ice) from the GLDAS model. Considering GRACE-based GWS data, the data fusion is further used to estimate monthly spatial maps of groundwater levels using time-varying spatial regression. Seasonal groundwater monitoring data are used in the training stage to identify spatial relations between groundwater level and GWS changes. Estimation of unknown groundwater levels through data fusion is accomplished by utilizing spatial coefficients that remain consistent with the nearest observed months. Monthly groundwater level maps show that the lowest groundwater level is 50 to 55 m below the earth’s surface in the state of Rajasthan. The accuracy of the estimated groundwater level is validated against observations, yielding an average RMSE of 2.37 m. The use of the GWS information enables identification of monthly spatial patterns of groundwater levels. The results will be employed to identify hotspots of groundwater depletion in India, facilitating efforts to mitigate the adverse effects of excessive groundwater extraction.

Measuring basin-scale aquifer storage change and mapping specific yield in Albuquerque, New Mexico, USA, with repeat microgravity data

Study RegionThe groundwater basin underlying the City of Albuquerque, New Mexico, USA. Study FocusThe study focuses on changes in groundwater storage and how those changes relate to groundwater-level changes. Groundwater storage change was measured using repeat microgravity at 35 stations from 2016 to 2021. Usually, storage is monitored by converting groundwater-level changes to storage changes using the aquifer storage coefficient, a difficult property to measure. With gravity, storage change can be measured directly. The storage coefficient, or specific yield in an unconfined aquifer, was estimated using the gravity method at individual sites, and a map created showing how this property varies over the region. New Hydrological Insights for the RegionFor the first time, a map of specific yield was produced based on interpolated maps of gravity-derived storage change and groundwater-level change, allowing inference of this property over a broad region even without collocated monitoring wells and gravity stations. Gravity data indicate aquifer drawdown and recovery mainly occurs in the central part of the basin where pumping is greatest. This spatial distribution is not captured by the more widely spaced monitoring well network. Because the aquifer is recovering from historically greater-magnitude pumping, net-neutral storage change (inflow=outflow) occurs when pumping from the central part of the well field is about 1.54 × 107 cubic meters (12,500 acre-feet) per year.

Experimental and Analytical Evaluations of Ground Behaviors on Changing in Groundwater Level in Bangkok, Thailand

Groundwater level changes have numerous effects on buildings, such as differential ground deformation and cracking on the wall. In Bangkok, Thailand, change in groundwater levels changing was caused by groundwater pumping that took place from 1978 to 1997. This is the main effect of ground deformation in a wide area of the Bangkok plain. According to the regulation of groundwater pumping in Bangkok and urban areas, the trend of groundwater level tended to recover around the year 1997. However, the ground settlement still occurs for a while after groundwater recovery. The objective of this study is to evaluate and compare the capability of each approach for the ground deformation and the pile capacity in the situation of groundwater level change. Data in this study were obtained from the previous centrifuge test which had been modeled for the Bangkok area. The ground behavior and pile load capacity behavior were verified using numerical modeling. Both experimental modeling and numerical modeling represent very similar trends of ground deformation. The pile capacity results from both models’ increase while the groundwater level decreases and the pile capacity decreases when groundwater is recovered. The numerical modeling results reveal an overestimate of the ground behavior. However, both results present the loss of pile capacity in the range of 8 to 25% of maximum load when the groundwater level reach to the minimum level.

Partition of Carbon Losses on CO2 Emission and Peat Subsidence in an Open-Drained Tropical Peatlands: A Consideration for Agroforestry Practices

Open-abandoned peatland commonly were not hydrologically well-managed in West Kalimantan causing continuous degradation of peat ecosystems, due to peat drying. This condition damage the carbon balance and function of tropical peatlands, result in significant greenhouse gas emissions. Tropical peat in the Kubu Raya District of West Kalimantan, which has a relatively large area of peat, has been degraded due to uncontrolled drainage and land fires caused by lack of management post the landcover changes. This study aims to clarify the partition of carbon loss in open peatlands due to the heterotrophic respiration (CO2 emission) process, which is part of the declining peat layer due to subsidence. The CO2 emission and subsidence assessments were accomplished for two years. The results show an increase in peat CO2 emissions to ~300% when groundwater level (GWL) lowered from ~0-5cm to >80cm. The trend is similar to the subsidence process due to changes in GWL. Carbon dioxide emissions range from 55,8 to 58,9% of peat layer losses, dependent on GWL. In undrained peatland, the CO2 emission was the lowest among others yet mainly loss in CO2 emission. The results of this study can provide considerations on small-holder agroforestry or other agricultural practices which wide-spread developed recently in this area. It is explaining the part of the subsidence that impacts the sources of CO2 emissions and practices to manage GWL to mitigate CO2 emission from open-drained peatlands.

Changes in groundwater flow in an unconfined aquifer adjacent to a river under surface recharge

ABSTRACT The groundwater level in an unconfined aquifer near a river is strongly affected by rainfall and river level. The linearized Boussinesq equation has been used in numerous studies to analytically investigate the changes in groundwater level. A perturbation method was used to determine the non-linear term of the Boussinesq equation. The generalized integral transform technique (GITT) was subsequently used to obtain a semi-analytical solution. We compared this solution with a linearized analytical and non-linear numerical solution and investigated the influence of each parameter that affects the number of convergent terms in analytical solutions. To estimate the recharge volume, two methods, the Horton infiltration formula and a method in which the fraction of rainfall intensity is considered, were employed. Subsequently, the simulated groundwater levels were compared with the field data. Finally, the recharge type, namely unimodal, with and without the Horton infiltration formula was used to model the groundwater flow.

Impact of various anthropogenic disturbances on water availability in the entire Mongolian basins towards effective utilization of water resources

In Mongolia, overuse and degradation of groundwater is a serious issue. The authors have recently applied a process-based eco-hydrology model, NICE (National Integrated Catchment-based Eco-hydrology) to urban and mining hubs to explicitly quantify spatio-temporal variations in water availability. In this study, NICE was scaled up to the total of 29 river basins in the entire country. The model simulated the effect of past climatic change and human activity on water resources during 1980-2018 there. The model reasonably reproduced observed river discharge with a maximal value during summer rainfall seasons. The simulation also revealed heterogeneous distributions of hydrologic budget and its response to climatic and anthropogenic disturbances. In addition, the authors detected hot spots of groundwater degradation by anthropogenic activity in the national scale. Analysis of relative contribution of environmental factors further clarified the characteristics in these areas and quantified spatio-temporal trends in groundwater level due to the effects of changes in precipitation and various water uses. Generally, the result showed changes in precipitation had a large effect on changes in groundwater levels until 2000. In contrast, the model clarified human activities have recently had a large impact on groundwater level changes. This trend was particularly conspicuous in river basins with urbanization and mining development such as Orkhon, Kharaa, Tuul, Galba, Ongi, Altain Uvur Govi, and Taats River Basins. This methodology is powerful to resolve future competition for water resources in areas with fewer inventory data that could potentially trigger conflicts between urban, mining, industry, herders and local communities.

Experimental assessment of structural responses of tunnels under the groundwater level fluctuation

Groundwater is one of the important factors affecting the stability of underground structures. However, the researches on the tunnel responses under the change of groundwater level based on the experiments are still insufficient. In this study, the interaction between underground tunnels and soil during the change of groundwater level in sand and clay stratums was investigated through the model experiments. Adopting the self-designed experimental equipment and innovative experimental methods, the contact pressure, bending moment, pore water pressure, buoyancy, and vertical displacement of two types of tunnels throughout the testing process were monitored. The impact of time lag effect on tunnels was also discussed. Force analysis indicates possible critical locations of both tunnels along the whole groundwater change process. The groundwater buoyancy in clay was reduced by time lag effect. The structures showed periodic sinking and floating behavior, and substantial settlement occurred with the decline of water level in the final stage.

Evaluation of basin-scale hydrogeological changes induced by reservoir operation at the Xiluodu dam site

Impoundment of large-capacity reservoirs has a great impact on groundwater flow in aquifer-aquitard systems. This impact occurs not only at the local scale in the dam area, but also at the regional scale under particular site conditions, causing unexpected geohazards and deformation phenomena. In this study, basin-scale hydrogeological changes induced by reservoir filling and operation at the Xiluodu dam site in southwest China are investigated by hierarchical numerical simulations. Hierarchical groundwater flow models consisting of a basin-scale model (34 km in horizontal dimension) and a site-scale model (4 km) are developed and solved with MODFLOW and a finite element code, respectively, by applying the output of the basin-scale model on the lateral boundaries of the site-scale model. The groundwater level changes in and the groundwater exchange between the confined and unconfined aquifer systems are evaluated. The groundwater level in the confined aquifer has significantly increased by about 96 m beneath the dam site since reservoir filling, and the dimension of the influence zone with an increase over 10 m in groundwater level reaches about 7–9 km in the basin. The rate of vertical leakage from the confined to unconfined aquifer first decreases during the initial filling, and then increases gradually as the pressure propagates into the confined aquifer. It is predicted that the dynamically equilibrated state will be reached in 2027. The local vertical leakage occurring in the plunge pool area along the unplugged boreholes drilled during site investigation is confirmed by a calculation based on the Theis formula. The results are useful for decision-making related to the reservoir operation and safety assessment of the dam.

Relationship of Rainfall Intensity with Slope Stability

The impact of rainfall on landslides is not an uncommon issue worldwide, including in Malaysia. It is a major challenge for geotechnical engineers to ensure the constructed slope is safe and can sustain longer periods of time, including during heavy rainfall. Kota Belud, Sabah, has been selected as the study area to meet the study objectives. Heavy rainfall has been recorded every year within Kota Belud, which has caused a repetition of landslide occurrences within the hilly areas, especially during the monsoon season. Presently, there is no local procedure for determining the rainfall intensity value for slope stability analysis. This study utilized the rainfall intensity value from Hydrology Procedure 26. Seepage analysis conducted shows rainwater infiltration has caused the groundwater level to increase from rainfall starts until 0.5 m below ground level and decrease after rainfall stops, creating fluctuations in the groundwater level during the wet and dry conditions within the wetting front. The factor of safety of the slope shows a decreasing trend, with a reduction of around 27 to 33% after 24 hours of rainfall in conjunction with the changes in groundwater level. However, the factor of safety increased by around 3% from the initial condition after 48 hours. The objective of this study is to identify the factor of safety of a rainfall-induced slope within Kota Belud utilizing the rainfall intensity design limits from Hydrology Procedure 26. Doi: 10.28991/CEJ-SP2023-09-06 Full Text: PDF