Bottom Slope Research Articles

Circulation and Retention of River Plumes Around Capes

AbstractRiver plumes often interact with capes in the coastal ocean, impacting local hydrodynamics and the transport of scalars. However, our current knowledge on how capes affect river plume separation, mixing, and retention is limited. Here, we conducted idealized numerical experiments with Gaussian‐shaped capes of varying curvature radii, constant river discharge, a sloping bottom, and scenarios with and without downwelling winds. We found that river plumes separate from capes when the Rossby number is above 1, a criterion that had not been tested for plume separation. This Rossby number is based on the plume velocity, the Coriolis factor, and the radius of curvature of the cape. Freshwater accumulation is greatest at the lee of narrow (i.e., pointy) capes under calm winds, but decreases significantly in downwelling winds or around broader capes.

Field Observations Reveal How Plunging Mixing and Sediment Resuspension Affect the Pathway of a Dense River Inflow Into a Deep Stratified Lake

AbstractThe pathway of dense river inflows into lakes, which affects the lake water quality, is not accurately predicted by existing models. The pathway of a dense riverine inflow in a lake with a submerged canyon is analyzed based on measurements during a 4‐month period of weakening lake stratification and weakening density excess between river and epilimnion. In line with models, the dense riverine inflow plunges upon entering the lake, continues as an underflow on the sloping lake bottom, and finally intrudes at its level of neutral buoyancy. Underflow and interflow velocities are O(0.1 m s−1). The river inflow is finally trapped in the pycnocline most of the time, even when the river's density excess and the lake's stratification are marginal. This trapping in the pycnocline is explained by the reduction of the inflow density excess due to the intense plunging mixing, which is an order of magnitude larger than that obtained in confined laboratory flumes. The pathway of the dense riverine inflow is affected by interactions of the underflow with the lake bottom and sedimentary processes. A canyon carved by the underflows confines and accelerates the underflow, which enhances its capacity to entrain and carry sediment. The entrainment of sediment that was previously deposited on the canyon bottom accelerates the underflow. Due to both effects, the underflow can temporarily break through the pycnocline and reach the hypolimnion. Existing models explain these observations qualitatively, but a quantitative prediction would require better parameterizations of the plunging mixing and the sedimentary processes.

Design and Planning of Mine Drainage Systems at PT. Pertama Mina Sutra Perkasa, Puger District, Jember Regency, East Java, Indonesia

PT. Pertama Mina Sutra Perkasa, a limestone mining company, operates in Grenden Village, Puger District, Jember Regency, East Java Province. Utilizing an open mining system, the company faces challenges related to mine drainage. Based on rainfall analysis from 2013 to 2020. the planned rainfall rate is 25.938 mm/hour, with a rainfall intensity of 5.712 mm/hour, resulting in a runoff water discharge of 0.599 m³/second. The water discharge entering the well at the site is 2159.08 m³/hour. The designed drainage channel has a discharge capacity of 3.109 m³/second, a wet surface area of 0.5 m², a channel bottom slope of 0.03%, a hydraulic radius of 0.25 m, a Manning roughness coefficient of 0.011. a wet cross-section circumference of 2 m, and a flow depth of 0.5 m. The planned well dimensions are 60 m in length, 20 m in width, and 7 m in depth, with a volume of 8400 m³. The current sludge settling pond has three compartments with a total capacity of 393.75 m³. The proposed design for the sludge settling pond includes a length of 60.6 m, a width of 15 m, a depth of 7 m, and a volume of 5454 m³. The actual mud dredging frequency is once every 2 days, while the proposed plan extends this interval to 9 days using a Doosan 340DX type excavator. This comprehensive drainage system design aims to efficiently manage runoff and sedimentation, ensuring sustainable mining operations

Evaluation of the Suitability of Using Artificial Neural Networks in Assessing the Effectiveness of Greywater Heat Exchangers

The use of greywater heat exchangers (GHEs) is an effective way to reduce energy consumption for heating domestic water. However, the available characteristics of this type of device are often insufficient and consider only a few selected parameters of water and greywater, which results in the need to look for tools enabling the determination of the effectiveness of GHEs in various operating conditions with incomplete input data. The aim of this paper was to determine the usefulness of artificial neural networks (ANNs). For this purpose, comprehensive experimental tests were carried out on the effectiveness of the horizontal heat exchanger, taking into account a wide range of water and greywater flow rates and temperatures of these media, as well as the linear bottom slope of the unit, which allowed for the creation of a database of 32,175 results. Then, the feasibility of implementing the full research plan was assessed using ANNs. The analysis showed that the impact of the media temperatures on the heat exchanger effectiveness values obtained using ANNs is limited, which makes it possible to significantly reduce the number of necessary experiments. Adopting only three temperature values of at least one medium allowed the generation of ANN models with coefficient values R2 = 0.748–0.999 and RMSE = 0.077–1.872. In the case of the tested GHE, the slope and the flow rate of the mixed water are of key importance. However, even in the case of parameters of significant importance, it is possible to reduce the research plan without compromising the final results. Assuming five different values for each of the four input parameters (a total of 625 combinations) made it possible to generate an ANN model (R2 = 0.993 and RMSE = 0.311) with high generalization ability on the full research plan covering 32,175 cases. Therefore, the conducted analysis confirmed the usefulness of ANNs in assessing the effectiveness of GHEs in various operating conditions. The approach described in this paper is important for both environmental and economic reasons, as it allows for reducing the consumption of water and energy, which are necessary to carry out such scientific research.

Metalimnion as an ecotone in stratified freshwater lakes: A case study on benthic testate amoebae in Lake Valdayskoe

Abstract Testate amoebae are widely used as bioindicators in the study of modern ecotopes and as proxies in palaeoecological reconstructions of lacustrine environments. The metalimnion with thermocline in stratified water bodies strongly affects the species structure of a number of aquatic animals and often plays a role as an ecotone for pelagic animals, but our knowledge on the influence of the metalinmion on benthic organisms, especially on testate amoebae, is still limited. This study aims to describe the influence of the metalimnion and its thermocline on benthic testate amoebae assemblages along a temperature gradient in the stratified freshwater Lake Valdayskoe. Twenty‐eight samples from nine sites were collected along the transect starting in the littoral zone, passing through a long metalimnion and its thermocline and finishing in the hypolimnion on the bottom slope. We identified four species assemblages, six non‐attributed samples and five morphotrait compositions in the transect, including those corresponding to the area inside the metalimnetic zone. We observed similarities in the transitions in benthic species assemblages, morphotype compositions, and species and morphotrait structures from shallow to deep water, and two shifts corresponded well with the upper and lower limnological boundaries of the metalimnion. The combination of the observed biological and hydrological characteristics suggests that the metalimnion plays a role of an ecotone between shallow and deep water in stratified freshwater lakes, and maintains the integrity and sustainability of benthic communities of testate amoebae. We explored a multivariate approach to demonstrate that the combination of highly abundant species and dominant morphotypes may be an efficient indicator of related environmental conditions. Thus, the high abundances of Cylindrifflugia acuminata, Centropyxis aculeata, Difflugia lacustris, D. linearis and C. discoides in combination with the dominance of elongate‐spiky and flattened‐spiky shells are closely related to the littoral zone with sandy sediments covered by many macrophytes. The combination of a high abundance of D. petricola and D. penardi, and the dominance of pyriform, necked and oval shells are closely related to deep depth. The studied species and morphotrait transition from littoral to deep water provides additional information about the morphological adaptations of testaceans, and about the processes of forming and maintaining benthic testate amoebae assemblages along the depth gradient. The described species and morphotrait assemblages related to specific water depths may be useful for palaeoreconstructions.

Coupling of sediment transport phenomena with turbulent surface flows: mathematical modeling, finite volume approximation and test simulations

Several sediment transport models coupled with shallow water equations have been developed in the literature over the past few decades. The water flow in the presence of abrupt bottom slopes distorts and cause turbulence. This phenomenon is well-known in the sediment transport theory. Sediment transport models based on shallow water equations do not include turbulence effects or the phase-lag between water velocity and bottom velocity. In this study, we consider a one-dimensional free surface turbulent water flow with sediment and morphodynamic. We propose a new one-dimensional acceleration-dissipation mathematical sediment transport model that considers the distortion of horizontal profile velocity in transport. The model is an improved version of existing averaged sediment transport models. In the new model, there is a distinction between fluid velocity and bottom velocity through a new bedload equation. The mathematical model is a system of nonlinear hyperbolic partial differential equations that are approximated by a stable and robust finite volume scheme presented in the path-conservative framework. Numerical tests are performed to demonstrate the efficiency of the developed theory.

A design of a nature-like fishway to solve the fractured river connectivity caused by small hydropower based on hydrodynamics and fish behaviors.

Achieving a harmonious alignment between the biological characteristics of fish and hydrodynamics patterns is crucial for ensuring the efficacy of fish passage facilities. In this study, based on the hydrodynamic characteristics of the river and the biological characteristics of fish, we evaluated the internal flow field in the nature-like fishway of Congen II hydropower station located along the Chabao river and explored methods to improve the operation efficiency. Based on comprehensive considerations of the flow field, turbulent kinetic energy, and the migration pathways of fish, it is found that the implementation of a continuous oblique bottom slope represents a more cost-effective and operationally convenient solution. The influence of different permutation of bulkheads in the nature-like fishway on operational efficiency was further examined. Our investigation revealed that the nature-like fishway with the continuous slope of 2% and the arrangement of three bulkheads in each row (model 3) exhibited a relatively simple velocity distribution and linear flow line, which poses challenges for fish in locating resting areas. In addition, the distribution of low turbulence kinetic energy area in the mainstream made it less favorable for fish to transition from the mainstream to the rest area within the fishway. The nature-like fishway with the continuous slope of 2% and the arrangement of two or three bulkheads in staggered rows (model 4) demonstrated better performance. Several potential fish migration routes for both model 3 and model 4 were proposed based on the numerical simulation results. In model 3, fish exhibited a continuous sprint through the concentrated high-speed area, which was less favorable for fish to rest and forage. In contrast, model 4 exhibited a diversified flow velocity distribution, enabling fish to make timely changes in their direction during migration. This feather proved to be advantageous in enhancing fish migration within the passage. The design of nature-like fishway in this study provides an important reference and technical support for the construction and optimization of the nature-like fishway for low dams, and is of great significance for restoring river connectivity destroyed by small hydropower construction and improving fish migration.

Roll waves in a predictive model for open-channel flows in the smooth turbulent case

A depth-averaged model for turbulent open-channel flows with breaking roll waves on a sloping smooth bottom is derived under an assumption of independence between the wall turbulence and the roller turbulence. The model includes four variables – the water depth, the average velocity, and two variables called enstrophy, the shear enstrophy and the roller enstrophy – which take into account the deviations of the velocity with respect to its depth-averaged value due to shear effect and roller turbulence, respectively. The four equations of the model are the mass, momentum, energy and shear enstrophy balance equations, with the mathematical structure of the Euler equations of compressible fluids, with an additional transport equation and with source terms. The system is hyperbolic. The roller enstrophy is created by shocks. A non-zero value of the roller enstrophy indicates a breaking wave and a turbulent roller. The model is solved by a fast and well-known numerical scheme, with an explicit finite-volume method in one step. The model is used to simulate periodic and natural roll waves with a good agreement with existing experimental results. There is no parameter to calibrate in the model, which gives it a predictive character.

Characterization Of Soils Derived From Sandstone In Effraya - Etung Local Government Area Of Cross River State, Nigeria

Pedological characterization of soils derived from sandstone in Effraya - Etung Local Government Area of Cross River State, Nigeria was studied with the view to suggesting appropriate management strategies. Three representative profile pits were dug in the summit, middle slope and valley bottom positions and the location of each profile was recorded with the aid of German Etrax 2000 GPS meter. The profile pits were described according to Soil Survey Staff. The soils were well drained in the summit and middle slope to poorly drained at the valley bottom and the soil color varied from very dark grayish brown to dark brown and also from yellowish brown to dark yellowish brown within the different horizons. Mean values of 65%, 23% and 12% were obtained in the surface soils for sand, silt and clay respectively while the textural class ranged from loamy sand to sandy loam in the surface and predominantly sandy clay loam in the subsurface soils. Bulk density and particle density had mean values of 1.2g/cm3 and 2.45g/cm3 with total porosity mean value of 48.5% for surface soils respectively. The strongly acidic soils were low in total nitrogen, organic carbon, available phosphorus, and exchangeable bases. CEC in the soils was moderately high with low ECEC while base saturation was below 50%. These results show that the soils are low in fertility and thus will require management practices such as liming, mulching, return of crop residues, and also planting of acid tolerant crops may be recommended for improved crop production.
 

Vegetation effects on radiation-induced natural convection in sloping water bodies

In this work, vegetation effects on the characteristics of radiation-induced natural convection (isotherms, circulation patterns, exchange flow rate) in sloping water bodies are investigated numerically. The water body consists of (a) a sloping vegetated region (with a bottom slope equal to 0.1) and (b) a deep region with a horizontal bottom. The vegetation of porosity 0.85 (typical of aquatic plants found in lakes) has a length equal to the length of the sloping region. It can block (totally or partially) the radiation and as a result a non-uniform (differential) heating is developed along the free surface of the water body. The Volume-Averaged Navier–Stokes equations together with the Volume-Averaged Energy equation are solved numerically in the vegetated region. The radiation-induced natural convection in a water body with only a sloping region (with no vegetation) is also considered for validation purposes since numerical and scaling analysis results are available in literature. The results indicate significant vegetation effects on the thermal and flow patterns especially for vegetation which blocks completely surface heating.

Laboratory observation of nonlinear wave shapes due to spatial varying opposing currents

Physical experiments were conducted to examine the influence of adverse currents on the propagation of shallower water waves and their impact on the evolution of nonlinear wave shapes. Irregular waves, characterized by varying initial peak periods and amplitudes, were generated in a physical wave flume equipped with a bottom slope of 1/20. Three groups of spatially varying opposing currents were generated in the flume and interacted with the aforementioned wave trains. Experimental results confirm that strong opposing currents can significantly intensify local wave nonlinearity, thereby further influencing the deformation characteristics of waves. In contrast, a weak opposing current (without wave-blocking) has a negligible effect. Bicoherence analysis revealed that the degree of phase coupling among triads of waves increased with an elevated current velocity before wave-blocking. Nevertheless, during partial wave-blocking, the degree of phase coupling was seemingly weakened by an increase in opposing current. Moreover, the influence of a co-existing current in the formation of extreme waves was recognized. The study confirms that adverse currents notably affect extreme wave steepness and extreme wave skewness, with a negligible impact on extreme wave asymmetry. As a result, empirical formulas modified by current effects are presented, describing certain key nonlinear wave shapes as functions of the local Ursell number.

The effects of bathymetry on estimating the depth of a source in range-dependent environments with a single hydrophone

The effects of varying or range-dependent bathymetry, e.g., such as a sloping bottom, on the depth resolution characteristics of single hydrophone matched field processing (MFP), e.g., width of depth main-lobe as a function of source and receiver nominal positions, is not well understood. A major challenge is that in the case of range-dependent environments there are generally no analytical representations for the pressure field, thus requiring numerical methods for their evaluation. To provide some theoretical insights into how the shape of the bathymetry and locations of the source and receiver influences the MFP depth ambiguity function, we study the case of an ideal wedge with perfectly reflective pressure-release boundaries using the analytical solutions of Buckingham [1]. We derive a simple approximation for the depth ambiguity function main lobe width and compare it against the theoretical result for an ideal range-independent environment [2] and then numerically for a penetrable wedge and more realistic shelf-like environments. M.K. Buckingham, “Acoustic propagation in a wedge-shaped ocean with perfectly reflecting boundaries,” NRL report 8793, March 1984. M. Cheney and I.P. Kirsteins, “Resolution of matched field processing for a single hydrophone in a rigid waveguide,” J. Acoust Soc. Am. 151, pp. 3186–3197, 2022.

Parameterizing Mesoscale Eddy Buoyancy Transport Over Sloping Topography

AbstractMost of the ocean's kinetic energy is contained within the mesoscale eddy field. Models that do not resolve these eddies tend to parameterize their impacts such that the parameterized transport of buoyancy and tracers reduces the large‐scale available potential energy and spreads tracers. However, the parameterizations used in the ocean components of current generation Earth System Models rely on an assumption of a flat ocean floor even though observations and high‐resolution modeling show that eddy transport is sensitive to the potential vorticity gradients associated with a sloping seafloor. We show that buoyancy transport coefficient diagnosed from idealized eddy‐resolving simulations is indeed reduced over both prograde and retrograde bottom slopes (topographic wave propagation along or against the mean flow, respectively) and that the reduction can be skilfully captured by a mixing length parameterization by introducing the topographic Rhines scale as a length scale. This modified “GM” parameterization enhances the strength of thermal wind currents over the slopes in coarse‐resolution, non‐eddying, simulations. We find that in realistic global coarse‐resolution simulations the impact of topography is most pronounced at high latitudes, enhancing the mean flow strength and reducing temperature and salinity biases. Reducing the buoyancy transport coefficient further with a mean‐flow dependent eddy efficiency factor, has notable effects also at lower latitudes and leads to reduction of global mean biases.

Evaluation of buoyant action of groundwater and surface water interaction on pit slope stability using hydrogeological-stratigraphic-structural assessment within the Kawere catchment of the Nsuta mine

ABSTRACT In open-pit mining operations where activities are conducted below water table or close to surface water bodies, the mine is potentially faced with dewatering and slope stability challenges. Appropriate evaluation of slope stability to obtain adequate slope safety factor has continuously been the centre of geotechnical research locally and internationally. This paper evaluates the influence of buoyant action propagated by groundwater and surface (GW-SW) interaction on pit slope designed in multi-layered fractured rock with complex hydrology using Hydrogeological-Stratigraphic-Structural Assessment (HSSA) at the Nsuta Manganese Mine in Ghana. LEM analyses of the Pit C-western slope estimated an overall factor of safety (FOS) of 1.1, probabilities of failure (POF) of 7.5% and the reliability index (RI) of 1.4 in the slope stress field. However, when the groundwater was introduced, the slope FOS was reduced to 0.13, POF of 100.0% and (RI) of 0.00 indicating failure. FEM numerical model points to the location of maximum shear strain and total displacement in the argillite zone within the rock mass. The FEM seepage analysis model estimated groundwater pore pressure data along the critical slide surfaces from the crest of the slope to the bottom of the rock slope ranging between 250 kPa and 4250 kPa with an average pore pressure of 2250 kPa within the pit slope. This proposed HSSA approach used in the study provides innovative insights into the percentage failure contribution of the individual lithologies to the overall combined lithological susceptibility of the slope under stress and groundwater failure mechanisms, pointing out Ru ratio in pit slope stability estimation as inadequate.

Initiation mechanism of shallow loess slope sliding under coupling effect of train vibration and rainfall

The large-scale construction and operation of the railway in Northwestern China has resulted in some geological disasters in recent times. Among them, the shallow sliding of the loess railway slope caused by the coupling effect of train vibration and rainfall has been a frequent occurrence, causing heavy losses of life and property. Accordingly, this is a major problem an needs an urgent solution. Therefore, this study used acceleration, pressure, moisture, and displacement monitoring equipment, among others, to conduct physical simulation experiments and theoretical analysis on the instability and sliding process of loess railway slopes under the coupling effect of train vibration and rainfall. The research results indicate that acceleration gradually decreases downward along the slope, and the pore water pressure and volumetric water content increase with the increase in rainfall infiltration. The slope displacement exhibits a phased increase after the initial slip. As vibration energy builds up, the slope bottom undergoes rapid structural damage and tensile shear coupled instability failure, followed by slip. Before sliding, both the crack density and fractal dimension of the slope have an active area, that is, a sliding slope area, which continues to expand upward under the cumulative effect of vibration energy. The failure process is divided into three stages according to the changes in macrodeformation, pressure, water content, displacement, and fractal dimension of the slope model: crack development stage, local liquefaction sliding stage, and slip propagation stage. This research elucidates the initiation mechanism of loess railway slope sliding under the coupling effect of train vibration and rainfall and provides a theoretical basis for predicting loess slope disasters under train vibration and providing adequate warning.

The impact of the geographical environment on the hydromorphological conditions of watercourses in southern Poland

Hydromorphological assessment of watercourses provides much valuable information about the riverbed and its immediate surroundings, including the influence of geographical environmental factors along with anthropogenic pressures in the catchment area. This paper presents diversity of hydromorphological conditions of 77 sections located on 39 watercourses in southern Poland in three European ecoregions: Eastern Plains, Central Plains and the Carpathians. The study was based on the Hydromorphological Index for Rivers (HIR) method and two sub-indices: Hydromorphological Diversity Score (HDS) and Hydromorphological Modification Score (HMS). Basic and multi-dimensional statistical analyses were performed to identify the main gradients of the geographical environment and the variables that contribute most to the total variability of HIR. The highest mean HIR values were recorded in the Carpathians ecoregion, then in the Central Plains and the lowest in the Eastern Plains, 0.70, 0.67 and 0.58, respectively. Significant differences were found between the Carpathians and Eastern Plains ecoregions in HIR values obtained. Hydromorphological differentiation is most influenced by altitude and geological type. The cluster analysis enabled two main groups of watercourses to be distinguished – the first one was dominated by variables showing HMS > HDS relationship, while the second one was dominated by HDS > HMS relationship. Multi-dimensional analysis provided additional information on the relationships between the variables and the sections studied. The greatest positive impact on the formation of the final HIR value had the variation of the riverbed slope and natural morphological elements of the bed bottom, while the greatest negative impact on HIR had the transformations observed in spot-check.

A Terrain-Following Control Method for Autonomous Underwater Vehicles with Single-Beam Sensor Configuration

This paper investigates the terrain-following problem for an autonomous underwater vehicle (AUV) from control perspectives with full consideration of terrain characteristics. By equipping the AUV with three simple single-beam echo sounders, a set of precise along-track bottom slopes are obtained in a real-time manner, and the occurrence of the lost bottom lock phenomenon caused by a single sonar altimeter is eliminated. A slope-based data processing method is developed, which enables an AUV to characterize seafloor features with complementary sensing modalities to generate proper adaptive height-modified values. In order to keep a fixed height when maneuvering over rugged terrains, a back-stepping depth control is implemented by adjusting horizontal rudder angle, and Lyapunov theory is adopted to analyze the asymptotic stability of the resulting terrain-following control system. At last, simulation results indicate the feasibility and effectiveness of the proposed methodology with a discussion of various sensor configurations.

A set of fully nonlinear mild slope equations

A set of time-dependent fully nonlinear mild slope equations is established in terms of velocity vector at still water level and free surface elevation, which is derived from the Euler equations without approximation in nonlinearity and only with the potential flow assumption adopted for bottom slope terms. Apart from the fully nonlinear property, the model is also different from previous nonlinear mild slope equations by adopting the velocity expression accurate to the first-order in bottom slope, which allows the new expressions of higher-order bottom slope terms to be established and the fully nonlinear terms related to bottom slope to be included in the equations. The model can be reduced to the classical mild slope equation for linear waves and the fully nonlinear Boussinesq equations for nonlinear waves. The advantages of the present model are validated against the related laboratory experimental results and demonstrated by comparison with the numerical results of other relevant models.

Numerical Investigation of the Optimal Inclination Angle of Sloped Bottom Tuned Liquid Damper

Numerical Investigation of the Optimal Inclination Angle of Sloped Bottom Tuned Liquid Damper

Diurnal heating and cooling of a sloping water body with vegetated shallow regions

In this work, diurnal heating, by solar radiation, and cooling in a sloping water body with vegetated shallow regions are investigated numerically. The sloping water body consists of a vegetated region with a bottom slope equal to 0.1 and a deep region with a horizontal bottom. The Volume-Averaged Navier-Stokes equations together with the Volume-Averaged Energy equation are solved numerically in the vegetated region. The latter has porosity equal to 0.85 (typical of aquatic plants found in lakes) and a length equal to the total length of the sloping region. At the top free surface, a time-dependent thermal forcing is applied, which is reduced in the vegetated region. Shallow water is considered with a maximum water depth being less than the penetration depth of the solar radiation. The non-vegetated sloping water body is also considered for validation purposes. The results (isotherms, streamlines, exchange flow rate), after ten full thermal forcing cycles, indicate significant vegetation effects on the daytime and night circulation and the exchange flow rates.