Dam Height Research Articles

Shoreline subsurface dams to protect coastal aquifers from sea level rise and saltwater intrusion

Fresh groundwater in arid and highly populated regions is limited. In coastal aquifers, the deterioration of fresh groundwater is accelerated by saltwater intrusion, primarily occurring through lateral encroachment and vertical movements in the proximity of discharging wells. Coastal regions have high salinity due to saline intrusion, where many abstraction wells are turned off by this high salinity, which leads to increased freshwater supply costs. This study investigates the performance of new approach using the shoreline subsurface dams (SSDs) for mitigating the saline water wedge in coastal aquifers, where the dams are installed at the shoreline (distance from shoreline = 0). Specifically, the current study's novelty is testing the effectiveness of SSDs by different relative heights ranging from 0.05 to 0.50 in the test case (Henry problem) and from 0.09 to 0.53 relative to the aquifer thickness in the field scale aquifer (Biscayne aquifer, Florida, USA). The results showed an exponential increase in salt repulsion for increasing SSDs height, reaching a maximum of + 0.70%, + 1.80%, + 3.25%, + 5.80%, + 10.45%, and + 18.40% for the dam height to aquifer thickness ratios of 0.09, 0.18, 0.26, 0.35, 0.44 and 0.53, respectively, in the field scale case. The SSDs increase the freshwater storage at the coastal zones where the low salinity occurs and reduces the freshwater supply cost. Despite the positive impact of height on repulsion, important factors such as economics, construction aspects, geographical suitability, and environmental impacts must be considered for real applications. This is crucial to develop feasible solutions applicable globally under the growing pressure of sea level rise.

Simulation of 0–7.5 Hz physics-based nonlinear ground motions for maximum credible earthquake scenarios at the Long Valley Dam, CA

We have conducted three-dimensional (3D) 0–7.5 Hz physics-based wave propagation simulations to model the seismic response of the Long Valley Dam (LVD), which has formed Lake Crowley in Central California, to estimate peak ground motions and settlement of the dam expected during maximum credible earthquake (MCE) scenarios on the nearby Hilton Creek Fault (HCF). We calibrated the velocity structure, anelastic attenuation model, and the overall elastic properties of the dam via linear simulations of a Mw 3.7 event as well as the Mw 6.2 Chalfant Valley earthquake of 1986, constrained by observed ground motions on and nearby the LVD. The Statewide California Earthquake Center (SCEC) Community Velocity Model CVM-S4.26.M01 superimposed with a geotechnical layer using [Formula: see text] information tapered from the surface to a 700-m depth was used in the simulations. We found optimal fit of simulated and observed ground motions at the LVD using frequency-independent attenuation of [Formula: see text] ([Formula: see text] in m/s). Using the calibrated model, we simulated 3D nonlinear ground motions at the LVD for Mw 6.6 rupture scenarios on the HCF using an Iwan-type, multi-yield-surface technique. We use a two-step method where the computationally expensive nonlinear calculations were carried out in a small domain with the plane wave excitation along the bottom boundary obtained from a full-domain 3D linear finite-fault simulation. Our nonlinear MCE simulation results show that peak ground velocities (PGVs) and peak ground accelerations (PGAs) as high as 72 cm/s and 0.55 g, respectively, can be expected at the crest of the LVD. Compared with linear ground motion simulation results, our results show that Iwan nonlinear damping reduces PGAs on the dam crest by up to a factor of 8 and increasingly depletes the high-frequency content of the waves toward the dam crest. We find horizontal relative displacements of the material inside the dam of up to [Formula: see text] and up to [Formula: see text] of vertical subsidence, equivalent to 1% of the dam height.

Experimental and numerical study on the breaching mechanisms of landslide dams with non-uniform structures

Landslide dams often exhibit non-uniform structures due to the rapid and dynamic accumulation of various types of landslide materials. These variations in dam composition significantly impact breach progression, causing significant errors in current model tests and numerical simulations with uniform structure assumptions This adversely affects peak flow predictions and decisions related to risk prevention and control. This study conducted a series of flume tests to examine the influence of non-uniform structures on the failure mechanisms of landslide dams. A 3D dam breach model was used to replicate these flume experiments and obtain more detailed information. Large Eddy Simulation (LES) captures the hydraulic features of dam-break flow, while equilibrium equations model morphological changes in landslide dams amid complex terrains using suspended and bed load transport. The findings indicate that in a uniform dam, the presence of coarse particles shifts erosion characteristics from layered erosion to step-pool development. Furthermore, as the content of coarse particles increases, the number of steps also rises. In the vertically non-uniform structure, the upper layer affects the formation of the breach, the middle layer affects the dam break and the breach flow, and the bottom layer affects the remaining dam height. The presence of an armor layer results in a higher water level and accelerates breach formation with a larger breach flow. In the horizontally non-uniform structure, the upper part of the overflow side is the core area of the breach, the lower part of the overflow side and the upper part of the opposite side affect the downcutting and widening rates of the breach, respectively. Preferentially, the breach tends to develop towards the relatively weaker of the two sides.

Study on Impoundment Deformation Characteristics and Crack of High Core Rockfill Dam Based on Inversion Parameters

In the numerical simulation of earth-rock dam, accurate and reliable mechanical parameters of the dam material are the important basis for dam deformation predictions and dam safety evaluations. Based on the deformation monitoring data of Luding core wall rockfill dam, the rheological parameters of rockfill and core wall materials are inverted in this paper. Combined with the actual filling and impoundment process of the dam, the numerical simulation is carried out, and the stress deformation and differential settlement of the dam after completion and impoundment are analyzed. The results showed that the stress deformation results of the dam based on the inversion parameters were in good agreement with the actual deformation. The horizontal displacement, settlement, and principal stress of the dam during the completion period were symmetrically distributed along the core wall. The maximum horizontal displacement occurred at the main dam on both sides of the core wall and the upstream and downstream dam slopes, and the maximum settlement occurred in the middle of the core wall. During the impoundment period, under the action of reservoir water pressure and upstream rockfill wetting deformation, the deformation and stress of the dam body no longer met the symmetrical distribution law, and the maximum horizontal displacement of the dam body during the impoundment period was located at 2/3 of the upstream dam slope. The maximum settlement of the dam body was located at 1/2 of the dam height. The maximum principal stress on the upstream side of the core wall was located on the left side of the bottom of the core wall, and the minimum principal stress was also located on the left side of the bottom of the core wall. The simulation results of the deformation and stress met the general law of earth-rock dam engineering. During the completion period, the deformation inclination of the dam crest was less than 1%. During the impoundment period, the deformation inclination of the dam crest area increased due to the wetting deformation of the upstream rockfill material. At the same time, the deformation inclination of the dam crest axis was larger than that of the upstream and downstream sides, and the deformation inclination of the dam crest at the middle of the valley was the largest, but it did not exceed 3%, that is, there would be no longitudinal cracks, which is consistent with the actual situation. The research results can better predict the stress deformation and crack of the dam body, and provide important support for dam safety evaluations.

The selection parameter for the operation and maintenance dam based on activity-based costing

Potential risks to people exist if a dam collapses and has a significant impact on the downstream area. Many countries are now facing the problem of having to deal with deteriorated infrastructure due to a lack of maintenance budgeting. This paper presents the dominant parameter in an Operational and Maintenance (OM) dam to build a cost estimation model to maintain the service life of the dam. The method used to identify cost-triggering parameters is based on activity-based costing and dam performance assessments using a combination of the modified Andersen, International Commission of Large Dams (ICOLD), and Dam Commission. The parameter was collected from fourteen independent variables, namely: dam height, irrigation area, sedimentation volume, grass area, wood vegetation area, corrosion area, concrete area, daily worker, corrosion expert, concrete deterioration, hydromechanical, physical performance, operation performance, and safety performance. The results of the model indicate that height, wood vegetation area, concrete maintenance area, hydromechanical deterioration, and safety performance are variables that affect OM costs. The OM costs can be reduced if the safety performance variable increases. This condition implies that if the safety performance component consists of dam monitoring activities, periodic inspections, green belt maintenance, water quality maintenance, and public awareness, the OM costs will decrease by 10%.

Hydrological Analysis Before and After Embankment-Raising Project of Agricultural Reservoir Watershed: A Case Study of Suyang Reservoir

We selected the SWAT hydrological model to analyze the hydrological changes before and after an embankment-raising project in agricultural reservoirs. The model was calibrated and validated from 2015 to 2016 using discharge data from the Songsan gauge station, which serves as a watershed outlet that includes the Suyang Reservoir. The dam height of Suyang Reservoir was raised from 13.5 m to 15.1 m, which resulted in a total storage capacity increase from 7.472 million cubic meters to 11.926 million cubic meters. The calibrated model demonstrates an efficiency of 0.9. Scenarios for pre- (2001-2012) and post-embankment raising (2014-2016) were simulated, and the results for various hydrological components (precipitation, runoff, infiltration, evapotranspiration, percolation, soil moisture, groundwater evaporation, and groundwater recharge) were summarized. The model results revealed average precipitation, runoff, infiltration, evapotranspiration, and groundwater recharge for the pre-embankment raising period (2001-2012) as 1,479.3 mm, 864.1 mm, 550.8 mm, 584.2 mm, and 165.0 mm, respectively. For the post-embankment raising period (2014-2016), the simulated values were 1,290.4 mm, 678.0 mm, 494.0 mm, 587.9 mm, and 145.9 mm, respectively. Below-average precipitation during the post-embankment raising period did not have a significant impact on the operation of the agricultural reservoir. The increased reservoir capacity through the embankment-raising project suggests the potential for additional water supply in the face of future water shortages and abnormal drought conditions. Additional research, including the determination of an appropriate water storage rate, will be necessary through long-term investigations and analyses, and climate change scenarios should be incorporated.

The effect of the check dam on the sediment transport and control in debris flow events

The implementation of check dams serves as a crucial measure in mitigating debris flow events, effectively stabilizing sediments and diminishing the magnitude of such occurrences. However, less attention has been paid to the fact that intact check dams also promote the release of sediment downstream, and the sediment control mechanism of the check dam during debris flow has not been clearly elucidated. In this study, according to the field survey data of the typical check dam and its surrounding sediment in Chutou Gully, several numerical flume models are built to explore the variation of the fluid kinetic energy and sediment alteration under the different channel gradients and different check dam setting patterns. An improved evaluation index for sediment transport of the check dam, DEItotal, is put forward to evaluate the sediment control efficiency of the established flume models. The results show the influence range of the check dam can be generally divided into positive and negative regions. The positive regions effectively intercept sediment, while the negative regions enhance the fluid erosion on sediment and promote the release of sediment. Both the positive and negative regions of the check dam are affected by the channel gradient and dam height. In addition, with the increase in sediment diameter, the resistance of sediment to fluid erosion is significantly improved.

Analysis of Stress and Deformation Characteristics of Different Dam Heights in Deep Overburden

Relying on an actual project, this paper carries out the application analysis and prediction research of the dam height 150m-200m concrete-faced rockfill dam on deep overburden. Through the finite element calculation results, the stress and deformation of the dam and the structural design of the seepage control system are analyzed. Several preliminary standards have been adopted to control its safety and provide a reasonable basis and technical support for the construction of a 150m-200m high dam on deep overburden.

Research on Dynamic Characteristics of Loess Homogeneous Dam under Seismic Waves

Based on the relevant provisions of the seismic design code, the three-dimensional nonlinear seismic response analysis of an actual loess homogeneous dam engineering is carried out. The seismic waves use the ground motion time history generated by the relevant design response spectrum of the set seismic site. The research results show that the homogeneous dam in the V-shaped valley has a significant amplification effect in the middle of the valley. The acceleration amplification area of the dam is above 4/5 of the dam height and within the range of 1/3 of the dam axis length. The regularity shows obvious "whiplash effect" and three-dimensional river valley effect.

Combined effects of aquifer heterogeneity and subsurface dam on nitrate contamination in coastal aquifers

Subsurface dams are effective for seawater intrusion mitigation, yet they can cause upstream nitrate accumulation. This research examines the interplay between subsurface dam construction and aquifer layering on nitrate pollution in coastal settings, employing numerical models to simulate density-driven flow and reactive transport. The study reveals that while subsurface dams are adept at curbing seawater intrusion, they inadvertently broaden the nitrate accumulation zone, especially when a low-K layer is present. Heterogeneous aquifers see more pronounced nitrate accumulation from subsurface dams. This effect is pronounced as it influences dissolved organic carbon dynamics, with a notable retreat inland correlating with the expansion of the nitrate pollution plume. A critical finding is that controlling seawater intrusion via dam height adjustment within the Effective Damming Region effectively reduces nitrate levels and bolsters freshwater output. However, exceeding the critical threshold—where the dam surpasses the low-K layer's bottom—results in a substantial shift in nitrate concentration, underscoring the need for precise dam height calibration to avoid aggravating nitrate pollution. This study's innovative contribution lies in its quantification of the nuanced effects of subsurface dams in stratified aquifers, providing an empirical basis for dam design that considers the layered complexities of coastal aquifers. The insights offer a valuable framework for managing nitrate contamination, thus informing sustainable coastal groundwater management and protection strategies.

Three-Dimensional Static and Dynamic Analyses of an Embedded Concrete-Face Rockfill Dam

Concrete-face rockfill dams have gradually become the preferred dam type in the engineering community. This study presents a hydropower station in China as a case study to introduce a new type of embedded concrete-face rockfill dam. The static and dynamic stress–strain characteristics of the proposed and conventional concrete-face rockfill dams were compared, and the optimal height of the embedded concrete body at the hydropower station was determined. The results indicate that, under static conditions, the embedded concrete body could reduce deformation upstream and downstream of the rockfill body, eliminate tensile stress along the concrete-face slab slope, reduce concrete-face slab deflection, and increase the maximum deflection area to 0.47 times the dam height. The inhibitory effect of the embedded concrete body on the stress and strain of the dam body became more evident as the size of the embedded body increased. Although the embedded concrete body did not enhance the dynamic and superposed static–dynamic stress states of the embedded concrete body and rockfill, the stress and strain increase in the dynamic state were within a controllable range. Through a sensitivity analysis and considering the terrain conditions and engineering cost of the hydropower station, the height of the embedded concrete body is recommended to be 0.4 times the dam height.

Two-phase modelling of erosion and deposition process during overtopping failure of landslide dams using GPU-accelerated ED-SPH

Erosion and deposition induced by overtopping flow strongly impacts the breaching evolution of landslide dams. However, these two processes are not yet sufficiently captured in current dam breaching models. In this paper, we simulate the Erosion and Deposition process during overtopping dam breaching using a novel Smooth Particle Hydrodynamics (ED-SPH) method. A new multi-function boundary is proposed to prevent the penetration of water and soil particles and ensure steady inflows. Dam break and movable erosion scenarios are simulated as a means to validate the model. Dam breach simulations using the ED-SPH method reveal that the proposed model can capture the complex dam soil erosion, entrainment, and depositions behaviors. The soil deposition hinders the eroded particle movement and reduces the water velocity at the water-soil interface. If soil deposition is not considered, as in many existing models, the breaching time decreases and the outburst flood discharge is magnified. We further investigate the re-erosion of deposited soils by varying the re-erosion coefficient. With decreasing the re-erosion coefficient, the peak discharge increases whereas the residual dam height decreases due to the blockage by the deposited soils.

Rainwater Harvesting of Some Catchment Areas in Mosul City/ Iraq by Small Dams Construction

In semi-arid and arid areas, there is little surface and groundwater. Consequently, efforts are being undertaken to protect and collect rainwater as much as possible. When the rainfall is irregular in arid and semi-arid regions, a large portion of it is lost as surface run-off creating a water shortage that puts people at risk. Water collection is a substitute in these circumstances and is crucial. Water harvesting is the process of collecting rainfall and run-off using various storage structures, such as tiny dams, primarily for human, agricultural, and livestock use. For the construction of storage structures to impound and harvest rain and run-off water, forming surface storage reservoirs, four sites with special hydrological and geomorphologic characteristics have been identified and pointed in the drainage map of the studied areas (Tal-Kaif, Zummar, Al-Shor, and Wadi-Almur). A dam model was created using a Global Mapper and Watershed Modeling System program, WMS. Each reservoir's geometrical dimensions and the overall volume of water held behind each site's dams were measured and computed. The four sites' combined storage capacity for water behind the dams might exceed (75×106) m3. Several dam heights were selected in each basin, and the submerged areas for each height were determined to select the optimal height in each basin, i.e., 11.75, 13.9, 9.8, and 12.3 m.

Study on the Control of Saltwater Intrusion Using Subsurface Dams

Subsurface dams are widely used to prevent saltwater intrusion, with good results. This blockage often leads to an accumulation of pollutants and salt on the inland and seaside of the dam, respectively. While the latter is intended, the former effect is not desired and poses a huge problem in groundwater management. In order to quantitatively address this issue and clarify the impact of subsurface dam height, location, and the head difference for the saltwater and freshwater boundary on saltwater wedges and fresh groundwater discharge, a flow tank and numerical model were constructed. The results indicate that there was an optimal effective dam height and location (also the minimum effective dam location) for controlling saltwater intrusion, which corresponded to the maximum groundwater and freshwater discharge. When the various conditions of the numerical model were set according to the flow tank and the dam was 15 cm away from the saltwater boundary, the minimum effective dam height was equal to the aquifer thickness multiplied by 0.36. The dam height reached a height that was slightly higher than the minimum effective height, namely, the ratio of dam height to aquifer thickness was 0.38, which revealed that the freshwater discharge reached its maximum at 22.71 cm3/min, the saline water wedge area was the smallest at 378 cm2, and the prevention effect of saltwater intrusion was the best. Building a dam too high, that was, the ratio of dam height to aquifer thickness exceeded 0.38, resulted in an increased saltwater wedge area and exacerbated aquifer pollution. When the dam was located at the minimum effective distance for preventing saltwater intrusion under a certain dam height and head difference between saltwater and freshwater boundary, that was, the ratio of the distance of the dam to the saltwater boundary to the total length of the aquifer was 0.063, the distance of the dam to the saltwater boundary was the minimum effective distance. Compared to other effective distances, when the dam was at the minimum effective distance, the freshwater discharge reached its maximum at 22.71 cm3/min, and the saltwater wedge area was the smallest at 378 cm2. These conclusions provide a theoretical reference for the impact of subsurface dam construction on the saltwater wedge. This study examines the impact of tides and waves on the water head of the saltwater boundary, and it is also necessary to verify these conclusions through actual field experiments. We will investigate this in future work.

Longevity prediction and influencing factor analysis of landslide dams

The longevity prediction and analysis of landslide dams are significant for evaluating the failure risks and formulating emergency plans. However, owing to the large range of landslide dam longevity (from “minutes” to “millennia”), both the analysis of influencing factors within different longevity ranges and a reliable longevity prediction model are still challenging. Based on 1045 landslide dam cases, the statistical analysis of the available data and longevity records is conducted. The landslide dam longevity is classified into seven categories (L1: <1 h, L2: 1 h to 1 day, L3: 1 day to 1 week, L4: 1 week to 1 month, L5: 1 month to 6 months, L6: 6 months to 1 year, and L7: >1 year). The k-Nearest Neighbor algorithm is used to impute the missing data for each longevity category. Based on geometric parameters (dam height, length, width, and volume), hydrological parameters (dammed lake volume and upstream catchment area), triggers, and dam materials, a longevity category classification model and a longevity numeric regression model are developed. The former is established for estimating the longevity range of landslide dams with an accuracy of 91%, and the latter is constructed with an R2 value of 0.95 for predicting precise longevity. Furthermore, the application of longevity prediction models proposed in this paper is verified by three landslide dam cases with reliable recorded data in the recent few years, while their predictive performance is also compared with that of conventional statistical models. Based on the SHapley Additive exPlanations attribution theory, the importance of geometric/hydrological parameters, triggers, and dam materials in determining the longevity of landslide dams in each longevity category is demonstrated using the complete database. Additionally, the influence level of each input variable on the prediction results is analyzed by examining the specific cases. The results indicate that the models proposed in this paper are superior to conventional statistical models in applicability and prediction accuracy. Notably, geometric parameters serve as the most important factor in each longevity category. Generally, the hydrological parameters can be regarded as the second most important factor in terms of influencing the longevity of landslide dams, while dam material demonstrates the lowest impact. The impact of triggers is more significant for landslide dams with a longevity of < 1 day. For landslide dams with a longevity exceeding one month, the importance of hydrological parameters is more prominent. Analyzing the impact of input variables on the prediction results of the specific landslide dams can facilitate the identification of key factors and provide some preliminary guidance for emergency rescue efforts.

A Toolbox for generalized pumped storage power station based on terrain in ArcGIS Environment

China proposed the goal of carbon peak by 2030 and carbon neutrality by 2060 at the 75th session of the United Nations General Assembly. Accelerating the development of clean energy is the key to achieve this carbon peak and neutrality goal. However, large-scale grid connection of new energy brings great challenges to the stable and safe operation of power grid. As a regulating power source and energy storage power source, pumped hydro energy storage (PHES) has strong regulating ability and is characterized as a reliable operation with broad prospects for development. However, the current field-survey-based method of site selection for PHES is time consuming, labour intensive, and costly. Improper site selection would cause ecological environment damages among other problems. A scheme or protocol that enables the automated site selection of PHES is therefore urgently required. The objective of this study was therefore to develop a new tool based on digital elevation model (DEM) and geographic information system (GIS) hydrological analysis function to screen out the potential PHES sites. ArcGIS, as a leading geospatial software, provides a set of geoprocessing (GP) tools for raster analysis. ArcPy is a Python package that runs in the ArcGIS environment. It can quickly invoke existing tools in ArcGIS to create custom extension modules. In this study, ArcPy was used to screen the site of PHES based on reservoir capacity and dam height, etc. Taking the southern Shaanxi Province, China as an example, comprehensive evaluation method integrating objective weighting method and multi-factor statistical analysis method is proposed and tested. This new method can promote the solution of the PHES site selection planning and preliminary reserve of PHES, and provide scientific reference and theoretical basis for the development and construction of PHES.

Experimental and Statistical Study on the Formation Characteristics and Discrimination Criteria of River Blockages Caused by Landslides

The discrimination of river blockages is very important for the risk assessment of landslide disasters and secondary hazards. Experimental studies and statistical analyses were carried out to explore the formation process and discriminant criteria of river blockages caused by landslides. An adjustable slide chute was designed and built to conduct forty-five landslide experiments. According to the experimental results, river blockage was identified as having six types based on the differences between the water depth and the height of the landslide dam, and the degree of river blockage increased from 70% to 100% as the chute angle, particle size, and landslide volume increased. It is also found that landslide volume controls the landslide dam height and degree of blockage, and particle size and slide angle control both the landslide velocity as it enters the river and the cross-section shape of the landslide dam. To investigate more influence factors, a statistical investigation of 60 real landslide cases was carried out, and it revealed that some geometric attributes related to landslide volume have the highest correlation with river blockage, especially landslide thickness. Finally, an improved probability model was proposed to assess the possibility of complete blockage, and it has overall accuracies of 91.1% and 83.3% when applied to predict experimental landslide cases and real landslide cases, respectively.

The impact of hydraulic conductivity anisotropy on the effectiveness of subsurface dam

Hydraulic conductivity is a key parameter controlling groundwater flow and solute transport, and anisotropy in hydraulic conductivity is common in aquifers. Previous studies have investigated the effectiveness of subsurface dams in combating seawater intrusion (SWI) and associated environmental concerns. However, the quantitative impact of hydraulic conductivity anisotropy on the performance of subsurface dam has not been explored. This study goes beyond previous research by examining, for the first time, the effects of subsurface dams on SWI prevention in anisotropic settings. Furthermore, the study optimized subsurface dam designs in anisotropic coastal aquifers through numerical simulations that take into account the environmental impact. Our findings reveal the mechanism of hydraulic conductivity anisotropy's influence on the discharging zone and demonstrate that as the anisotropy ratio (rk) decreases, the coastal discharging zone expands landward, reducing SWI and ultimately lowering the minimum effective dam height (MEDH). This process effectively prevents SWI while maximizing fresh groundwater discharge. Increasing the rk values simultaneously expands both the MEDH and the peak fresh groundwater discharge (PFGD). Additionally, increasing the horizontal hydraulic conductivity of the aquifer significantly increases the range of PFGD, while the distance between the dam and shoreline emerges as the main factor influencing the extent of the MEDH.

Dynamic Responses of Concrete-Face Rockfill Dam to Different Site Conditions under Near-Fault Earthquake Excitation

The western region of China is rich in hydropower resources and characterized by unique geological conditions. For the construction or planned construction of high dams in this region, different types of cover layers are formed due to special geological structures, most of which are located in high seismic intensity zones. This study focuses on four different site conditions: hard ground, medium–hard ground, medium–soft ground, and weak ground. By simulating the dynamic response of concrete-face rockfill dams under near-fault earthquake excitation, the vertical settlement of the dam and the attenuation of seismic motion under different site conditions are analyzed. The research findings reveal a consistent trend where the vertical settlement of the dams progressively escalates with increasing dam height across all four site conditions. This settlement phenomenon is especially pronounced in weak ground conditions, posing a potential risk of failure. Furthermore, when subjected to near-fault pulse-type earthquake motions, the existence of weak soil layers significantly dampens the seismic forces experienced by the dam. This finding suggests that the weaker the geological conditions of the site, the more pronounced the attenuation effect of the seismic motion. Additionally, the overburden layers have a noticeable amplification effect on near-fault pulse-type earthquake motion. However, this amplification effect is not significant in weak ground, possibly due to the presence of weak soil layers restricting the propagation and amplification of seismic motion. In conclusion, these research findings have practical significance for the dynamic response of high dam construction in different site conditions in the western region of China. They provide a scientific basis for the design and construction of high dams and serve as a reference for the implementation of seismic mitigation measures and earthquake disaster prevention in engineering projects.

Effect of mixed physical barrier on seawater intrusion and nitrate accumulation in coastal unconfined aquifers.

Physical barrier has been proven to be one of the most effective measures to prevent and control seawater intrusion (SWI) in coastal areas. Mixed physical barrier (MPB), a new type of physical barrier, has been shown to have higher efficiency in SWI control. As with conventional subsurface dam and cutoff wall, the construction of MPB may lead to the accumulation of nitrate contaminants in coastal aquifers. We investigated the SWI control capacity and nitrate accumulation in the MPB using a numerical model of variable density flow coupling with reactive transport, and performed sensitivity analysis on the subsurface dam height, cutoff wall depth and opening spacing in the MPB. The differences in SWI control and nitrate accumulation between MPB and conventional subsurface dam and cutoff wall were compared to assess the applicability of different physical barrier. The numerical results show that the construction of MPB will increase the nitrate concentration and contaminated area in the aquifer. The prevention and control efficiency of MPB against SWI is positively correlated with the depth of the cutoff wall, reaching the highest efficiency at the minimum effective dam height, and the retreat distance of the saltwater wedge is positively correlated with the opening spacing. We found a non-monotonic relationship between the change in subsurface dam height and the extent of nitrate accumulation, with total nitrate mass and contaminated area increasing and then decreasing as the height of the subsurface dam increased. The degree of nitrate accumulation increased linearly with increasing the height of the cutoff wall and the opening spacing. Under certain conditions, MPB is 46-53% and 16-57% more efficient in preventing and controlling SWI than conventional subsurface dam and cutoff wall, respectively. However, MPB caused 14-27% and 2-12% more nitrate accumulation than subsurface dam and cutoff wall, respectively. The findings of this study are of great value for the protection of coastal groundwater resources and will help decision makers to select appropriate engineering measures and designs to reduce the accumulation of nitrate pollutants while improving the efficiency of SWI control.