Land Use and Land Cover Dynamics in the Eseka Alluvial Gold Mining District, Centre Region, Cameroon

Local populations in Cameroon thrive on forest resources and the flow of ecosystem services they provide are pivotal in sustaining national economy, improving people’s lives, safeguarding biodiversity, and mitigating the impacts of environmental changes. The exploitation of these resources invariably leads to deforestation and forest degradation. This study was designed to evaluate land use land cover change (LULCC) in the Eseka alluvial gold mining district with the aid of Landsat images. In the investigation of forest cover change, four Landsat satellite images for (1990, 2002, 2015 and 2022) were used. Ground-truthing also helped to identify the activities carried out by the local population and to determine agents, drivers and pressures of land use and land cover change. Four main land cover classes namely: forest, agricultural land, settlement/mining camps and water bodies were selected. Between 1990 and 2022, the proportion of forest decreased from 98% to 34% while those of agricultural land and settlement/mining camps increased from 2% to 60% and 0.54% to 6% respectively. Analysis showed ongoing deforestation with forest cover loss of ~98,263 ha in 32 years giving a cover change percentage of 63.94%. Kappa coefficient for the study period ranged from 0.92 to 0.99. Forest cover loss could be attributed to farming activities, wood extraction and alluvial gold mining activities. Economic motives notably the need to increase household income from a frequent demand for farm and wood products in neighbouring towns and the quest for gold were the main drivers of these activities. Hence, this study assesses the impact of human activities from the mining sector on the forest ecosystem in a bid to inform mitigation policies.

Collaborative Effect of Fines on Changes in Grain Distribution in the Process of Improving the Geotechnical Properties of an Alluvial Gravel 0/14

The technical and economic optimization of road projects has led to research into the use of materials obtained by mechanical stabilization for pavement construction. This research has enabled us to outline a solution capable of giving the sub-base layer the necessary and sufficient capacity to support the induced loads forecast for the traffic. This work evaluates the effect of adding fine silty clay (Cl) and clayey silt (Csp), two corrective materials to alluvial gravel (0/14), the main material, in the process of improving its cohesion and geotechnical properties. The results obtained show that the optimum mix is obtained with 10% by weight of Cl and 15% Csp. The granulometry of the mixes is spread out, but poorly calibrated. The Ag-Cl mixtures made at 10%, 15%, 20%, 25% 30% and Ag-Csp at 15%, 20%, 25%, 30%, and 35%, do not obey the law of mixtures. Mixing with 10% Cl reduces the sand equivalent of alluvial gravel by 60.23%, while mixing with 15% Cl reduces the sand equivalent by 6.82%. The addition of correctors increases the optimum water content and fine sand content of the mixes. Increasing the fine sand content reduces the optimum dry density, CBR index and static modulus. Mixes containing 10% Cl and 15% Csp have CBR values of CBRCl (96%) and CBRCsp (84%) and are not suitable for pavement base layers. In fact, the hardness of the grains has a Los Anges value of 41%, higher than the maximum permitted by the standard of 35%. The mixes obtained can be used as pavement base layers for traffic levels in a cumulative number of heavy goods vehicles 5 × 105 6 for an approximate life of 15 years.

Flood risk on arid alluvial fans:a case study in the Joghatay Mountains,Northeast Iran

Among the common hazards related to alluvial fans,flooding is one of the most important.Nonetheless,in populated alluvial fans,not only the natural processes are effective in floods,but the artificial structures and modifications can change the behavior of flooding and its potential risks.This study aims to indicate the flood-prone landforms in a set of populated alluvial fans in an arid region and investigate the role of anthropogenic activities in controlling/exacerbating flooding in alluvial fans.To achieve this goal,15 Ground Range Detected in High resolution(GRDH)SAR Sentinel-1 images,covering a total of 24 alluvial fans,were acquired.Pre-processing and post-processing steps were applied to all images to identify flood-prone sections of the studied alluvial fans.The results showed that feeder channels,spreading sites,and wide interfluves are the most flood-prone landforms of alluvial fans.In terms of anthropogenic modifications to mitigate flooding,a rampart system is distributed in the study area.Ramparts are levee like structures formed from the fan material.They aim to mitigate flood hazard on residential areas,infrastructures,and agricultural lands of the study area.Results show that the rampart system can reduce the danger of floods,but it cannot be considered a long-term solution.Therefore,a comprehensive flood protection system distributed throughout the whole alluvial fan system is needed.Results also reveal that in regions where flood monitoring is challenging,SAR images can be used as a freely available data set to monitor and identify flooding hotspots.

The Influence of Alluvial Mining on the Morphology and Ecological Health of the Jhimruk River in Pyuthan, Nepal

Historically, alluvial rivers have been a desirable source of sediment for various industrial purposes. However, the demand for sand is rapidly increasing, leading to environmental concerns associated with its extraction. The extraction of sediment from riverbeds has both visible and invisible effects. This research aims to investigate the dynamics of the Jhimruk River’s morphology and its impacts by evaluating the river’s quality and studying its changing morphology. To assess morphological changes, satellite images from different years were compared using Geographic Information System (GIS). Physical assessments were conducted by calculating a Habitat score based on various parameters. Water quality assessments involved measuring factors such as pH, temperature, nitrate levels, and alkalinity. A water quality map of the river was generated using color coding to indicate different conditions. The Habitat score demonstrated variations in the data collected from all sites, with factors such as instream cover, bottom substrate stability, riparian vegetation, and aesthetic of the river stretch playing crucial roles in influencing the total score. The Water Quality Index value for the disturbed site indicated moderate pollution, falling under class II. Aquatic macroinvertebrates displayed natural responses to increasing levels of stressors across their life stages, as observed through the analysis of the GRS-BIOS/ASPT index. With the exception of the disturbed site, all other sites were classified under water quality class II, while the disturbed site belonged to class III, indicating a moderate to critically polluted state for most of the Jhimruk River. Furthermore, an increase of 180.87 meters in the river width at the disturbed site provided evidence of morphological changes occurring over the specified period. Mining activities were identified as a significant contributor to the alteration in river morphology.

Combined Chemical and Mineralogical Evidence for Heavy Metal Binding in Mining- and Smelting-Affected Alluvial Soils

The binding of metallic contaminants （Pb, Cd, and Zn） and As on soil constituents was studied on four highly contaxninated alluvial soil profiles from the mining/smelting district of Pribram （Czech Republic） using a combination of mineralogical and chemical methods. Sequential extraction analysis （SEA） was supplemented by mineralogical investigation of both bulk samples and heavy mineral fractions using X-ray diffraction analysis （XRD） and scanning electron microscopy with an energy dispersive X-ray spectrometer （SEM/EDS）. The mineralogy of Fe and Mn oxides was studied by voltammetry of microparticles （VMP） and diffuse reflectance spectrometry （DRS）. Zinc and Pb were predominantly bound in the reducible fraction attributed to Fe oxides and Mn oxides （mainly birnessite, Na4Mn14O27.9H2O）, which were detected in soils by XRD and SEM/EDS. In contrast, Cd was the most mobile contaminant and was predominantly present in the exchangeable fraction. Arsenic was bound to the residual and reducible fractions （corresponding to Fe oxides or to unidentified Fe-Pb arsenates）. SEM/EDS observations indicate the predominant affinity of Pb for Mn oxides, and to a lesser extent, for Fe oxides. Thus, a more suitable SEA procedure should be used for these mining-affected soils to distinguish between the contaminant fraction bound to Mn oxides and Fe oxides.

Upper Cretaceous alluvial fan deposits in the Jianglangshan Geopark of Southeast China:implications for bedrock control on Danxia landform evolution

The Jianglangshan Geopark in the western Zhejiang Province of Southeast China is well-known for its spectacular red-colored sandstone landforms. Little is known about the depositional processes of the conglomerate-dominated Fangyan Formation, the lithologic base of the Danxia landforms in this geopark. Based on detailed field investigation of lithology, sedimentary structures, bed thickness and geometry, five facies are recognized: facies A(matrixsupported cobble conglomerate), facies B(pebble conglomerate), facies C(pebbly sandstone), facies D(fine-grained sandstone) and facies E(mudstone). The results show that streamflow-dominated fans were the main depositional processes responsible for the accumulation of the Fangyan Formation along the mountain fronts. These fan conglomerates form the base for the evolution of the Danxia landscapes owing to the uplift and erosion of the study area. In contrast, the fine-grained sedimentary successions produced by fluvial floodplains in the distal part of the fans were thinner and more easily weathered. Such sedimentary facies distribution patterns were thought to be similar during Late Cretaceous across Southeast China. The Danxia landforms are largely the geographical expressions of the conglomerate-dominated redbeds in the proximal-middle fans.

Seismic analysis of semi-sine shaped alluvial hills above subsurface circular cavity

In this study, a seismic analysis of semi-sine shaped alluvial hills above a circular underground cavity subjected to propagating oblique SH-waves using the half-plane time domain boundary element method(BEM) was carried out. By dividing the problem into a pitted half-plane and an upper closed domain as an alluvial hill and applying continuity/boundary conditions at the interface, coupled equations were constructed and ultimately, the problem was solved step-by-step in the time domain to obtain the boundary values. After solving some verification examples, a semi-sine shaped alluvial hill located on an underground circular cavity was successfully analyzed to determine the amplification ratio of the hill surface. For sensitivity analysis, the effects of the impedance factor and shape ratio of the hill were also considered. The ground surface responses are illustrated as three-dimensional graphs in the time and frequency domains. The results show that the material properties of the hill and their heterogeneity with the underlying half-space had a significant effect on the surface response.

Free Oxide Distribution in Poorly and Well Drained Soils Developed on Calcareous Alluvial Deposits

A study on the distribution of free iron and manganese oxides was conducted in soils developed on calcareous alluvial deposits under subhumid climatic conditions, in Western Greece. Soil samples from two well drained soils and from two poorly drained soils, classified as Alfisols, were collected and used in this study. After certification of soil homogeneity the acid ammonium oxalate and dithionite-citrate-bicarbonate methods were used to extract free iron and manganese oxides from the samples. Iron oxides extracted by the dithionite-citrate-bicarbonate method (Fed) were significantly higher than the iron oxides extracted by the ammonium oxalate method (Feo), indicating that a considerable fraction is present in crystalline forms,independent of drainage status. A confirmation of free iron oxides and fine clay was detected. The ratios Feo/Fed and (Fed-Feo)/total Fe (Fet) could not be used to distinguish the well drained soils from the poorly drained soils. Manganese movement in a soluble form is independent of the fine clay.

Diffraction of plane P waves around an alluvial valley in poroelastic half-space

Diffraction of plane P waves around an alluvial valley of arbitrary shape in poroelastic half-space is investigated by using an indirect boundary integral equation method. Based on the Green＇s fimctions of line source in poroelastic half-space, the scattered waves are constructed using the fictitious wave sources close to the interface of the valley and the density of ficti- tious wave sources are determined by boundary conditions. The precision of the method is verified by the satisfaction extent of boundary conditions, and the comparison between the degenerated solutions and available results in single-phase case. Finally, the nature of diffraction of plane P waves around an alluvial valley in poroelastic half-space is investigated in detail through nu- merical examples.

Detecting Dynamics of Hot Topics with Alluvial Diagrams:A Timeline Visualization

Purpose： In this paper, we combined the method of co-word analysis and alluvial diagram to detect hot topics and illustrate their dynamics. Design/methodology/approach： Articles in the field of scientometrics were chosen as research cases in this study. A time-sliced co-word network was generated and then clustered. Afterwards, we generated an alluvial diagram to show dynamic changes of hot topics, including their merges and splits over time. Findings： After analyzing the dynamic changes in the field of scientometrics from 2011 to 2015, we found that two clusters being merged did not mean that the old topics had disappeared and a totally new one had emerged. The topics were possibly still active the following year, but the newer topics had drawn more attention. The changes of hot topics reflected the shift in researchers＇ interests. subdivided and re-merged. For example, several topics as research progressed. Research topics in scientometrics were constantly a cluster involving ＂industry＂ was divided into Research limitations： When examining longer time periods, we encounter the problem of dealing with bigger data sets. Analyzing data year by year would be tedious, but if we combine, e.g. two years into one time slice, important details would be missed. Practical implications： This method can be applied to any research field to illustrate the dynamics of hot topics. It can indicate the promising directions for researchers and provide guidance to decision makers. Originality/value： The use of alluvial diagrams is a distinctive and meaningful approach to detecting hot topics and especially to illustrating their dynamics.

Effects of land uses on soil physic-chemical properties and erodibility in collapsing-gully alluvial fan of Anxi County,China

the National Key Technologies R＆D Program of China during the 12th Five-Year Plan period （2011BAD31B00）

3D scattering of obliquely incident plane SV waves by an alluvial valley embedded in a fluid-saturated, poroelastic layered half-space

The indirect boundary element method is used to study the 3D dynamic response of an infinitely long alluvial valley embedded in a saturated layered half-space for obli- quely incident SV waves. A wave-number transform is first applied along the valley＇s axis to reduce a 3D problem to a 2D plane strain problem. The problem is then solved in the section perpendicular to the axis of the valley. Finally, the 3D dynamic responses of the valley are obtained by an inverse wave-number transform. The validity of the method is con- firmed by comparison with relevant results. The differences between the responses around the valley embedded in dry and in saturated poroelastic medium are studied, and the effects of drainage conditions, porosity, soil layer stiffness, and soil layer thickness on the dynamic response are dis- cussed in detail resulting in some conclusions.

How do stream processes affect hazard exposure on alluvial fans? Insights from an experimental study

Alluvial fans are among the most privileged settlement areas in many mountain regions. These landforms are particularly dynamic being episodically affected by distributary processes generated by extreme flood events. Addressing risk assessment entails determining hazard exposure and unravelling how it might be related to process loading and to process dynamics once the flow becomes unconfined on the surface of alluvial fans. By following a ‘similarity of process concept’, rather than by attempting to scale a real-world prototype, we performed a set of 72 experimental runs on an alluvial fan model. Thereby, we considered two model layouts, one without a guiding channel and featuring a convex shape and the other one with a guiding channel, a bridge, and inclined but planar overland flow areas as to mirror an anthropic environment. Process magnitude and intensity parameters were systematically varied, and the associated biphasic distributary processes video recorded. For each experiment, the exposure was detected by mapping the exposed area in a GIS, thereby discerning between areas exposed to biphasic flows and the associated depositional phenomena or to the liquid flow phase only. Our results reveal that total event volume, sediment availability and stream power in the feeding channel, as well as depositional effects, avulsion, and channelization on the alluvial fan concur to determine the overall exposure. Stream process loading alone, even when rigorously defined in terms of its characterizing parameters, is not sufficient to exhaustively determine exposure. Hence, further developing reliable biphasic simulation models for hazard assessment on settled alluvial fans is pivotal.

AN ANALYTICAL SOLUTION FOR THREE-DIMENSIONAL DIFFRACTION OF PLANE P-WAVES BY A HEMISPHERICAL ALLUVIAL VALLEY WITH SATURATED SOIL DEPOSITS

An analytical solution for the three-dimensional scattering and diffraction of plane P-waves by a hemispherical alluvial valley with saturated soil deposits is developed by employing Fourier-Bessel series expansion technique. Unlike previous studies, in which the saturated soil deposits were simulated with the single-phase elastic theory, in this paper, they are simulated with Biot＇s dynamic theory for saturated porous media, and the half space is assumed as a single-phase elastic medium. The effects of the dimensionless frequency, the incidence angle of P-wave and the porosity of soil deposits on the surface displacement magnifications of the hemispherical alluvial valley are investigated. Numerical results show that the existence of a saturated hemispherical alluvial valley has much influence on the surface displacement magnifications. It is more reasonable to simulate soil deposits with Biot＇s dynamic theory when evaluating the displacement responses of a hemispherical alluvial valley with an incidence of P-waves.

Sufficiency and Deficiency Indices of Soil Available Zinc for Rice in the Alluvial Soil of the Coastal Yellow Sea

To determine the sufficiency and deficiency indices of soil available Zn by the Agro Services International （ASI） method （ASI-Zn） for Zn fertilizer recommendation in rice production in the alluvial soil of the coastal Yellow Sea, the relationship between relative rice yield and soil available ASI-Zn concentration was analyzed from a ten-field experiment with various soil test classes ranging from low to high fertility in 2005 and 2006, and nine Zn fertilizer application rates （0, 7.5 15, 22.5, 30, 37.5, 45, 52.5 and 60 kg Zn/ha） arranged at random with three replications in each field. There was a significant quadratic relationship between soil available ASI-Zn and rice yield, and a significant linear relationship between soil available ASI-Zn concentration and Zn fertilization rate. For rice variety Wuyujing 3, soil available ASI-Zn was deficient when the value was at lower than 1 mg Zn/L, low at 1 to 2 mg Zn/L, sufficient at 1 to 2 mg Zn/L, excessive at higher than 7.5 mg Zn/L. Thus, Zn fertilizer recommendation could be done according to the sufficiency and deficiency indices of soil ASI-Zn. For most of alluvial soils of the coastal Yellow Sea in the study, the available ASI-Zn was lower than 1 mg Zn/L, and then the optimum application rate of Zn fertilizer was about 20 kg Zn/ha.

Surface Motion of Alluvial Valley in Layered Half-Space for Incident Plane P-Waves

The indirect boundary element method (IBEM) is used to study the surface motion of an alluvial valley in layered half-space for incident plane P-waves based on Wolf’s theory. Firstly, the free field response can be solved by the direct stiffness method, and the scattering wave response is calculated by Green’s functions of distributed loads acting on inclined lines in a layered half-space. The method is verified by comparing its results with literature and numerical analyses are performed by taking the amplification of incident plane P-waves by an alluvial valley in one soil layer resting on bedrock as an example. The results show that there exist distinct differences between the wave amplification by an alluvial valley embedded in layered half-space and that in homogeneous half-space and there is interaction between the valley and the soil layer. The amplitudes are relatively large when incident frequencies are close to the soil layer’s resonant frequencies.

Seismic responses of a hemispherical alluvial valley to SV waves: a three-dimensional analytical approximation

Abstract An analytical solution to the three-dimen-sional scattering and diffraction of plane SV-waves by a saturated hemispherical alluvial valley in elastic half-space is obtained by using Fourier-Bessel series expan-sion technique. The hemispherical alluvial valley with saturated soil deposits is simulated with Biot＇s dynamic theory for saturated porous media. The following conclusions based on numerical results can be drawn： （1） there are a significant differences in the seismic response simulation between the previous single-phase models and the present two-phase model; （2） the nor-malized displacements on the free surface of the alluvial valley depend mainly on the incident wave angles, the dimensionless frequency of the incident SV waves and the porosity of sediments; （3） with the increase of the incident angle, the displacement distributions become more complicated; and the displacements on the free surface of the alluvial valley increase as the porosity of sediments increases.

DYNAMIC ANALYSIS OF PIPELINES LAID THROUGH ALLUVIAL VALLEY

This paper describes the dynamic characteristics of pipelines laid through alluvial valleys. We assume that the alluvial valley has a semi-cylindrical cross-section. The ground motion of alluvial valley under harmonic seismic SH waves is carried out, and the pipeline-soil dynamic interaction is taken into account. Though simple, the model may qualitatively explain the earthquake damages of pipelines laid through an alluvial river valley.

Origin and Distribution of Heavy Minerals in the Surficial and Subsurficial Sediments of the Alluvial Nile River Terraces

Origin and distribution of the heavy minerals of surficial and subsurficial sediments has been investigated in the alluvial Nile River terraces, Khartoum North, Sudan. Heavy mineral assemblages in the very fine sand fraction (0.063 - 0.125 mm) of 10 sediment samples were identified using petrography microscope. Results of descriptive statistical parameters revealed that most sediments samples belonged within very poorly sorted to extremely poorly sorted, strongly negative skewed to strongly positive skewed and mesokurtic to very leptokurtic. The quartz was the dominant in the opaque minerals in all sediments. The non-opaque heavy minerals were dominant by zircon, tourmaline, rutile, garnet, sillimanite, and andalusite. Results revealed that the ultrastable minerals (zircon, tourmaline and rutile) were found in all sediments with range from (2% - 47.36%, 2.08% - 29% and 3% - 24.99%), respectively. Garnet, sillimanite and andalusite were also found with range from (5% - 67%, 1% - 9.09% and 1% - 50%), respectively. Heavy mineral assemblage indentifies sources that are not bounded to the local origin. The proportion and presence of heavy minerals from outside source rocks indicated relatively strong reworking of zircon sand from the outer-shelf to inner-shelf as well relatively long distance of transport. Fluvial and Aeolian sediments were the dominant environments in the investigated area. We conclude that most heavy minerals in the study area are originally derived from gneisses and schist metamorphic rocks and some igneous rocks of the Ethiopian plateau.

The Effect of Alluvial Foundation on the Earth Dams Settlement

Careful monitoring in the earth dams, to measure deformation caused by settlement and movement has always been a concern for engineers in the field. In order to measure settlement and deformation of earth dams, usually the precision instruments of settlement set and combined Inclinometer that is commonly referred to IS instrument, will be used. In some dams, because the thickness of alluvium is high and there is no possibility of alluvium removal (technically and economically and in terms of performance), there is no possibility to place the end of IS instrument (precision instruments of Inclinometer-settlement set) in the rock foundation. Inevitably, have to accept installing pipes in the weak and the deformable alluvial foundation that this leads to errors in the calculation of the actual settlement (absolute settlement) in different parts of the dam body. The purpose of this paper is to present new and refine criteria for predicting settlement and deformation in earth dams. The study is based on conditions in three dams with a deformation quite alluvial (Agh Chai, Narmashir and Gilan-e Gharb) to provide settlement criteria affected by alluvial foundation. To achieve this goal, the settlement of dams was simulated by using finite difference method with FLAC3D software and then the modeling results were compared with reading IS instrument. In the end, the caliber of the model and validate the results, by using regression analysis techniques and scrutinized modeling parameters with real situations and then by using MATLAB software and Curve Fitting Toolbox, a new criteria for the settlement based on elasticity modulus, cohesion, friction angle, density of earth dam and alluvial foundation was obtained. The results of these studies show that, by using the new criteria measures, the amount of settlement and deformation for the dams with alluvial foundation can be corrected after instrument readings and the error rate in reading IS instrument can be greatly reduced.