Critical Water Depth Research Articles

Hydrological Connectivity Response of Typical Soil and Water Conservation Measures Based on SIMulated Water Erosion Model: A Case Study of Tongshuang Watershed in the Black Soil Region of Northeast China

The black soil region of Northeast China is the largest commercial grain production base in China, accounting for about 25% of the total in China. In this region, the water erosion is prominent, which seriously threatens China’s food security. It is of great significance to effectively identify the erosion-prone points for the prevention and control of soil erosion on the slope of the black soil region in Northeast China. This article takes the Tongshuang small watershed (Heilongjiang Province in China) as an example, which is dominated by hilly landforms with mainly black soil and terraces planted with corn and soybeans. Based on the 2.5 cm resolution Digital Elevation Model (DEM) reconstructed by unmanned aerial vehicles (UAVs), we explore the optimal resolution for hydrological simulation research on sloping farmland in the black soil region of Northeast China and explore the critical water depth at which erosion damage occurs in ridges on this basis. The results show that the following: (1) Compared with the 2 m resolution DEM, the interpretation accuracy of field roads, wasteland, damaged points, ridges and cultivated land at the 0.2 m resolution is increased by 4.55–27.94%, which is the best resolution in the study region. (2) When the water depth is between 0.335 and 0.359 m, there is a potential erosion risk of ridges. When the average water depth per unit length is between 0.0040 and 0.0045, the ridge is in the critical range for its breaking, and when the average water depth per unit length is less than the critical range, ridge erosion damage occurs. (3) When local erosion damage occurs, the connectivity will change abruptly, and the remarkable change in the index of connectivity (IC) can provide a reference for predicting erosion damage.

A cellular automata model for dynamically describing the overland flow and sediment transport

Rainfall erosion has been calculated and predicted by various soil loss equations, but the progressions of overland flow and sediment transport are less dynamically described. In this study, cellular automata (CA) models based on single flow direction algorithm (SFD), average value multi-flow direction algorithm (AMFD) and remaining average value multi-flow direction algorithm (RAMFD) were constructed. Simultaneously, erosion model was constructed by dividing soil erosion into inter-rill, rill and gully erosions according to critical water depth. The CA models were validated at three scales: a theoretical slope, an in-situ model slope and the natural basin. The results demonstrated the efficient performance of RAMFD in the runoff ascension and recession stages while SFD and AMFD presented unconcentrated runoff distribution, especially in the in-situ slope and basin simulation. Besides, RAMFD model occurred sediment deposition in the basin upstream while SFD and AMFD presented continuous erosion. Furthermore, the runoff Nash-Sutcliffe efficiency (NSE) of three models were 0.85 ∼ 0.95 and 0.65 ∼ 0.94, and the erosion root mean square error (RMSE) were 0.5 ∼ 1.0 kg/min and 0.3 ∼ 0.45 102kg/min in the theoretical slope and natural basin, respectively. Meanwhile, the NSE and RMSE values of RAMFD exhibited the best performance, indicating that this model effectively balanced water distribution while controlling the flow direction to a greater extent. Overall, it is justified to develop an erosion prediction model based on the classification of erosion types, and the rules governing water flow allocation will inevitably result in qualitative and quantitative differences of runoff and erosion.

Theoretical, experimental, and numerical studies of flow field characteristics and incipient scouring erosion for slope with rigid vegetations

Under the action of continuous rainfall, the coupling linkage between runoff and seepage can cause erosion of non-cohesive soil particles on vegetated slopes. A nonlinear turbulent-seepage coupling model is established to study the flow field characteristics and incipient scouring erosion of the vegetated slope. The fluid in the turbulent region is governed by the Reynolds averaged Navier-Stokes. Biot's poroelasticity theory describes the flow in the vegetation region. The seepage in the soil region obeyed the Darcy-Brinkman equation. Analytical solutions of the vertical velocity profile and safety factor (sliding and rolling) of the particle incipient motion are derived based on the coupling between turbulence and seepage. The velocity expression is found to be in good agreement with the existing experimental data of both emerged and submerged vegetation conditions, respectively. The velocity distribution above the surface follows a logarithmic pattern, while below the surface, non-linear seepage occurs with a transition layer that deviates from Darcy seepage. In addition, the particle incipient motion is verified by the physical flume souring test under none, sparse, and dense vegetation, respectively. The absolute error between the theoretical calculation and the physical test is within 5%. Furthermore, the critical water depth is nonlinearly negatively correlated with the energy slope. Finally, a CFD-DEM coupling numerical model is employed to further observe the scouring erosion of the sparse and dense vegetated slopes with the same conditions as the physical test. The numerical results show that the scouring erosion exhibits discontinuous behavior and the soil particles between the two vegetation are more vulnerable to scouring than those in other locations. After scouring, the inertial porosity of the vegetated soil slope decreases while the porosity in the surface area increases.

Whitecapping term analysis of extreme wind wave modelling considering spectral characteristics and water depth

The Simulating WAves Nearshore (SWAN) model can be used to simulate extreme wind waves such as tropical cyclone waves, which are of great significance for the study of coastal processes and the protection of coastal engineering. In this study, the basic setting and whitecapping term of the SWAN model are analysed to model tropical cyclone waves, with spectral characteristics and water depth taken into account. By investigating the temporal variation of bulk wave parameters and wave spectral characteristics of key nodes, the optimal values of 4 basic setting parameters are determined. By analysing the sensitivity of tuning effects of key coefficients in different whitecapping formulations, calibration criteria of these parameters are provided, and the coefficients Stpm and Powk in the Komen formulation are found to be most sensitive to the outputted significant wave height and mean wave period, respectively. To further study the sensitivity of these coefficients, especially their relationship with water depth, spatial analyses of sensitivity variations are performed in the coastal region, which show that the sensitivity of these coefficients increases first and then tends to be stable with the increase of water depth, indicating a critical water depth between 20 m and 50 m. This study provides insights for more effective and directional modelling of tropical cyclone waves in coastal and shelf seas.

Impact of an energy dissipator on mooring conditions in ultra-high head locks with a comprehensive uniform-strength evaluation

In high head locks, the energy dissipator directly affects the safety and stability of the ships moored in locks. However, most existing studies used physical model tests to determine mooring conditions. This inevitably lengthened the construction period and increased investment costs for the pre-construction of high head locks. In this study, a comprehensive uniform-strength Cs criterion was established and used to quantify critical water depth of ship impact and judge the mooring conditions. We used the mooring force of 60 m class ultra-high head single-stage locks as a study case and conducted a comparative analysis by the physical model ship. Results showed that this method effectively responded to the influence of different energy dissipators (ditch, ditch + grille, and ditch + cover plate) and configuration types within the mooring conditions of the lock chamber. Additionally, this study investigated the hydraulic factors affecting regional forces and wave forces, and found that energy dissipators types mainly affect regional force for mooring conditions in ultra-high head decentralized water transfer systems. Considering comprehensive efficiency and energy-dissipation effects, we recommend ditch + grille dissipator for ultra-high head locks. This study provides an effective discriminative technique for optimizing the arrangement of high head locks and saving project investment.

The Effect of the Water Table on the Bearing Capacity of a Shallow Foundation

Immersion is an important part of reservoir engineering investigation and evaluation. Determining the reasonable and effective burial depth of the critical immersion water table is one of the key scientific issues in the impact assessment of the bearing capacity of reservoir immersion foundations. In this study, basic physical and mechanical property tests were carried out on the soil in the typical immersion area of Xiaonanhai Hydropower Station, and the influence mechanism of saturation on the mechanical properties of building foundation soil and immersion on the bearing capacity of a shallow foundation was obtained. According to the test results, the influence depth of the rising groundwater level on the stability of the building foundation is analyzed, and a method to determine the critical depth of immersion groundwater in the reservoir is proposed. Taking the typical building foundation of Luohuang Town in the immersion area of Xiaonanhai Reservoir as an example, the validity of the critical water depth is further verified. The results show that the safety limit depth of the independent foundation affected by the rise of the water table increases with the increase of the width of the foundation and decreases with the increase of the buried depth of the foundation. Considering the safety limit depth, the critical depth of building immersion is 4.830 m, and without considering the safety limit depth, the critical depth of building immersion is 4.05 m. To a certain extent, it can reduce the impact of water table changes on the bearing capacity of shallow foundations.

Geotechnical Issues in Decommissioning Surface Lignite Mines—The Case of Amyntaion Mine in Greece

Recent changes in the fossil-fuel energy sector require coal mining industries to plan for the future, including developing procedures for decommissioning and closure associated with mines. In surface coal mining, the geotechnical issues of decommissioning include the long-term stability of the pit slopes, particularly as the pit is gradually filled with water. This paper investigates such slope stability issues, with emphasis on the conditions prevailing in the Amyntaion surface lignite mine, in Western Macedonia, Greece. Analytical and numerical methods have been developed and used to estimate the temporal evolution of the overall safety factor, as the water level in the pit rises, creating a lake. It is shown that until the water level in the lake reaches a critical depth of approximately 15–35% of the final equilibrium condition, the safety factor against the overall slope instability decreases slightly (by about 3% in the case study, and up to 5–10% in other conditions) compared to its value at the end of exploitation. At higher lake levels, the safety factor increases significantly, as the beneficial effect of the lake water pressure acting on the slope overcomes the adverse effect of pore water pressure rise inside the slope. In typical mines, the critical water depth is achieved within a few years, since the surface area of the pit is smaller at deeper levels; thus, more favorable slope stability conditions are usually reinstated a few years after mine closure, while the small reduction in safety during the initial stages after closure is inconsequential. The paper investigates the parameters influencing the magnitude of the small reduction in the short-term safety factor and produces normalized graphs of the evolution of the safety factor as the lake water level rises. The results of the analyses can be used in preliminary closure studies of surface coal mines.

Assessing the Performance of LISFLOOD-FP and SWMM for a Small Watershed with Scarce Data Availability

Flooding events are becoming more frequent and the negative impacts that they are causing globally are very significant. Current predictions have confirmed that conditions linked with future climate scenarios are worsening; therefore, there is a strong need to improve flood risk modeling and to develop innovative approaches to tackle this issue. However, the numerical tools available nowadays (commercial and freeware) need essential data for calibration and validation purposes and, regrettably, this cannot always be provided in every country for dissimilar reasons. This work aims to examine the quality and capabilities of open-source numerical flood modeling tools and their data preparation process in situations where calibration datasets may be of poor quality or not available at all. For this purpose, EPA’s Storm Water Management Model (SWMM) was selected to investigate 1D modeling and LISFLOOD-FP was chosen for 2D modeling. The simulation results obtained with freeware products showed that both models are reasonably capable of detecting flood features such as critical points, flooding extent, and water depth. However, although working with them is more challenging than working with commercial products, the quality of the results relative to the reference map was acceptable. Therefore, this study demonstrated that LISFLOOD-FP and SWMM can cope with the lack of these variables as a starting point and has provided steps to undertake to generate reliable results for the need required, which is the estimation of the impacts of flooding events and the likelihood of their occurrence.

Waves Generated by Discrete and Sustained Gas Eruptions With Implications for Submarine Volcanic Tsunamis

AbstractSubmarine volcanic eruptions can perturb the water surface and subsequently generate localized tsunamis. Herein waves are produced in analogous laboratory experiments by injections of non‐condensable expanding air into fresh water. By varying source pressures, jet durations and water depths, we obtain two key results. There exists a saturation duration above which the maximum wave height will not increase as the eruption continues. Apart from in extremely shallow or deep water depths, this saturation duration is positively correlated with the source intensity and negatively with the water depth. There also exists a critical water depth where an eruption with a given source intensity can generate the largest waves. When an eruption lasts less than the saturation duration, increasing the eruption duration will increase the critical water depth and the corresponding maximum wave height. The saturation duration and critical water depth are the primary controls on tsunami size and hazard.

Laboratory Experiments on Tsunamigenic Discrete Subaqueous Volcanic Eruptions. Part 2: Properties of Generated Waves

AbstractSubmarine volcanic eruptions have the potential to generate tsunamis, which can cause destruction well beyond the range of the eruption itself. Here, we present a series of underwater eruption experiments in which a non‐condensing gas was injected into a water tank with a range of water depths and applied pressures. This study proposes an effective scaled water depth and categorizes underwater eruptions into three types: deep‐water eruptions, intermediate‐water eruptions, and shallow‐water eruptions. In deep‐water eruptions, most of the energy is dissipated within the water column before the plume reaches the surface, and negligible waves are generated. In intermediate‐water eruptions, reductions in water depth reduce the loss of energy to the water column, leaving more energy available for wave generation. This causes an increase in wave heights as water shallows, up to a point. In sufficiently shallow‐water cases, the water depth is so small that almost all of the energy from the eruptive jet or plume passes through the water and is dissipated into the air, so there is only small wave‐making potential, even with relatively intense source strength. Therefore, there exists a critical water depth at which an eruption with a given source intensity will generate the largest waves. That depth lies at the boundary between the intermediate‐ and shallow‐depth regimes, where the energy available for wave generation is at a maximum. This research reveals fundamental wave generation mechanisms related to underwater gas eruptions, thereby extending our understanding of submarine volcanic tsunami generation and providing a foundation for future hazard assessment.

The influence of finite depth on the evolution of extreme wave statistics in numerical wave tanks

Model tests with unidirectional random wave fields are common for coastal engineering purposes. In this paper, we investigate the finite water depth effect on both the probability of extreme events and the averaged shape of them in such experimental conditions. We simulate some typical model test conditions with a numerical tool, which solves the fully non-linear wave equations. We find the analytical solution based on Nonlinear Schrödinger equation (NLS) to be accurate for low steepness and relatively deep water cases. However, the analytical solution underestimates the kurtosis at the steady state for high steepness cases in shallow water, and also gives zero value of kurtosis at critical water depth, whereas a small but non-zero value of kurtosis is observed in the numerical tank. We also investigate the averaged shape of the extreme events, which are modified by nonlinear physics over the distance. The horizontal asymmetry is significant initially but is greatly reduced to a steady state, and the contraction of the wave groups grows monotonically until the steady state is reached along the wave tank. Finite water depth has limited effects on the averaged shape of large events, especially for the extremely steep waves.

Critical Water Depth Features over Broad-Crested Weirs.(Dept.C)

The characteristics of flow over suppressed broad-crested weirs have been extensively studied by old and recent investigations, while for contraeled ones, the studies are limited. In the present study, the charaeteristies of the critical water depth over the contracted weirs were investigated. The effects of the different weir geometrical ratios and different flow parameters on the critical water depth locations were discussed. Experiments were conducted on a laboratory flume and the measured data were analyzed. An empirical equation, in terms of the weir and the flow parameters was developed to predict the critical water depth over the broad-crested weirs. Another empirical equation was also developed 10 predict the location of the critical water depth over such weirs. A good agreement was found between the developed equations and the experimental observations of die present study and that of others. Hence, the passing flow discharge becomes easy to be determined using one of the developed empirical equations and applying the discharge equation in terms of the esitical water depth in a rectangular open channel.

Critical Water Depth and Installation Curves for Submarine Cable Deployment Process

The purpose of the present paper is to propose installation curves for submarine cable deployment process for different water depths and tension deployment, emphasizing on the importance of modelling the “out of water” cable segment and the friction force between cable and overboard chute of the installation vessel. A custom-made analysis tool has been further expanded and used for the calculation of the cable hydraulic critical responses. Moreover, the concept of the critical water depth is proposed analytically for first time to define the cases in which the “out of water” cable segment can be ignored without denoting the accuracy of the minimum bending radius calculation. In addition, correction factors are proposed in relation to water depth and bottom tension values in order to eliminate the error of the safety factor calculation. Numerical formulation of the friction has been incorporated in the custom-made analysis tool as a further development. The analysis of various cable deployment cases proves that the inclusion of the “out of water” segment in the analysis is critical in shallow water areas. In contradiction, the modelling of the friction force is critical in deep water areas. However, both parameters are potential causes of important analysis errors.

IMPROVED DESIGN CRITERIA FOR EXTENDING BRIDGE-LIKE INTAKES INTO OPEN CHANNELS

Extended water intakes are structures established at river sides to divert water for multiple uses and purposes. Previous studies have only focused on extending the intake to a sufficient water depth for ensuring permanent abstraction. They used physical and numerical models to predict the trend of the site riverbed morphological changes for identifying the lowest bed levels and biggest depths to which intakes could be extended. However, they have ignored other parameters that govern the extension. This paper aims to investigate those parameters and introduce a practical and scientific basis that helps estimate the minimum (min) offshore extension distance of a water intake. It is the distance between the point where the annual min water stage meets the channel bank and the point where a critical water depth is sufficient to submerge the suction pipe inlet without producing vortices that affect both the pumping system and channel bed. Based on the definition of the extension distance, the critical water depth under the min water stage at the channel cross section concerned has to be computed. By analyzing the min water stage, it was found that it is equal to the sum of a submergence depth, the diameter of the suction pipe inlet or (the strainer length), and a clearance distance above the channel bed. Doing further analysis, it was found that the submergence depth value depends on the water station discharge requirements, the water suction velocity at the pipe inlet, and the maximum height of a water wave generated by a moving navigation boat near the intake as well as the channel bed morphology. Also, the value of the clearance distance above the bed was found to be a function of the suction pipe diameter or (the strainer length). To compute the min extension distance, a Spreadsheet Model was developed to correlate all the concerned parameters and help study as many scenarios as possible to find the most economical and safest distance. Finally, the research concluded that the computation of the min extension distance is governed by a number of factors such as the min water stage, water station discharge requirements, water suction velocity at the pipe inlet, and maximum water wave height generated by a moving boat near the intake.

Nonlinear simulation of shape-preserving delta growth

In this paper, we demonstrate the existence of shape-preserving (self-similar) delta. We focus our study on a Gilbert-type delta growing by the sediment discharged at the river mouth. The evolving velocity of the shoreline depends on its local geometrical configuration including the water depth, repose angle, and curvature. Linear analysis of this local model suggests that when the sediment supply to the shoreline front can be maintained at a constant value, unstable growth occurs for adverse bathymetry (back-tilted basement) and there exists a critical water depth that leads to a self-similar evolution. A novel nonlinear analysis based on a rescaling idea reveals that there exists a critical flux Jc at the shoreline such that a desired shoreline shape can be achieved and maintained self-similarly independent of the water depth information, though the critical flux Jc may depend on the water depth. We then develop a semi-implicit numerical method to investigate the nonlinear dynamic of the shoreline. Our numerical results are in excellent agreement with the linear theory when the shape perturbation is small, and confirm that in the nonlinear regime the shoreline may evolve self-similarly under Jc. In particular, we demonstrate that a prescribed shoreline morphology can be achieved by a well-designed Jc. The existence of shape-preserving growing delta goes beyond the well known dynamical patterns and highlights the feasibility of shape control.

H2 SU YÜZÜ PROFİLİNE SAHİP AÇIK KANAL AKIMININ SAYISAL MODELLEMESİ

In open channel flows, 12 different surface profiles are formed depending on the flow conditions.The occur of water surface profiles varies depending on the upstream and downstream waterdepths, bed slope and the geometric characteristics of the interacted structure. The relation of the measured water depth without any structure with the critical water depth, formed in situation ofcritical flow, are used in the classification of the flow profiles. Open channel flows with differentwater surface profiles have been investigated experimentally in detail by researchers. Because ofadvances in technology in recent years, it is possible to solve governing equations bycomputational fluid dynamics methods. Computational fluid dynamics methods, which are moreeconomical than experimental models, are frequently used in solving hydraulic problems. In thisstudy, numerical solutions of open channel flow with different water surface profiles arecalculated. The turbulence shear stress in numerical modeling is calculated by using the ReNormalization Group (RNG) model and the water-air intersection is determined by using theVolume of Fluids (VOF) method. Experimental measurements in the literature and numericalmodel results are compared. The numerical model is found to be successful in determining thewater surface, especially in the drop region where H2 profile is formed.

Experiment on morphological and hydraulic adjustments of step‐pool unit to flow increase

AbstractExceptional flood events with a return period of about 50 years can be destructive to step‐pool channel segments. However, field investigations and flume experiments have not examined the hydraulic and morphological feedbacks of step‐pool morphology during unsteady hydrographs of exceptional flood events. We performed a series of flume experiments with a manually constructed step model, perturbed with three hydrographs that varied in the rate of water supply change. The bed texture, topography, flow regimes, surface flow field and water depth were characterized and measured as the flow rate was increased during the experiments. A distinct pool feature emerged downstream of the manually constructed step when the flow rate exceeded the threshold scaled to the peaks of ordinary flood events in well‐graded mountain streams. The pool feature was modified in several different ways with flow rate increase. The bed surface steadily coarsened, micro‐bedforms developed and became more pronounced, the bed topography became more spatially complex based on analysis using the Hurst exponent, and last, pool depth steadily increased. Pool modification was also linked to the flow regime: the impinging jet regime led to grain size segmentation in the pool while the jump regime contributed to decelerating flow velocity. The steeper rising limb of hydrograph led to a less developed pool feature, with smaller sized micro‐bedforms in the pool bottom to outlet, and higher discharge threshold for distinct coarsening and scouring in the pool. The estimated energy dissipation within the step‐pool unit decreased as a power function from low to high flow, quantified as the ratio hc/HS, where hc is the critical water depth and HS is scour depth. Our results highlight the interaction between morphology, hydraulics, and energy dissipation of step‐pool unit and the crucial role of hydrograph shape on the interaction during flow increase © 2019 John Wiley & Sons, Ltd.

The effect of roughness and rainfall on hydrodynamic properties of overland flow

AbstractOverland flow is the initial driver of slope surface erosion. To discover resistance characteristics of overland flow influenced by rainfall intensity and roughness, indoor simulated rainfall experiments with six kinds of roughness, five flow discharges, and five rainfall intensities were investigated. Results showed that overland flow over rough surfaces could be considered as laminar and turbulent flow when using flow Reynolds number. According to roll waves observed, flow regimes belonged to the laminar transitional zone based on the viscosity-to-depth ratio. A critical water depth formula for overland flow was re-derived, and it showed that this test water flow consisted of supercritical flow in most cases, and subcritical flow in only a few cases. The flow resistance coefficient increased with increasing roughness, whereas it decreased as rainfall intensity increased. Considering the ‘increasing resistance’ phenomenon, this study focused on frictional resistance, thickness of the viscous sublayer, pressure drag and roll waves. Finally, a formula for sheet flow resistance was proposed based on resistance segmentation and multi-element linear regression. These findings are of significance both for understanding the characteristics and development of overland flow and overland flow dynamics.

Estimating ecological flows for fish overwintering in plain rivers using a method based on water temperature and critical water depth

AbstractEcological flow is the foundation for conservation of riverine fish habitat and ecosystem. Habitat models have been widely used to estimate ecological flow owing to their integration of hydrological regime and species hydraulic preference. Previous studies based on habitat methods focused more on the spawning season but paid less attention to the winter period, which is also essential to fish life stage. This study developed a novel approach to estimate the ecological flow for fish overwintering, particularly in plain rivers. The water depth for target fish safely overwintering was firstly determined based on the minimum tolerable water temperature of the species. A water balance model was built to estimate the ecological flow for securing the determined water depth. The developed approach was applied in the middle reaches of Huaihe River, where the flow is highly regulated by dams and sluices. Parabramis pekinensis was selected as the target fish, and the minimum water depth for it to overwinter in the river was about 20 m. The calculated ecological flow was 3.0 m3·s−1 in December, 2.2 m3·s−1 in January, and 2.1 m3·s−1 in February, respectively. The approach contributed a great supplement to fish spawning habitat model, and their combination could determine ecological flow regimes for the entire life cycle of the target fish.

Visualization of Specific Energy for Open Channel Flow in Three Dimensions

Specific energy is the total head with respect to the channel bottom. It is a summation of the velocity head and the depth of flow at a given cross section. Specific energy has proven to be very useful in the analysis of open channel flow and the concept is discussed in every open channel book. Usually, the discussion is illustrated by 2-dimensional plots of depth vs. specific energy with discharge as a parameter and/or depth vs. flowrate with specific energy as a parameter. Obviously, these graphs depict slices through a surface in a three-dimensional space whose coordinates are depth, discharge, and specific energy. Furthermore, the plots are almost invariably displayed only for rectangular cross sections, and the three-dimensional specific energy surface is rarely shown. Using graphical software, this paper displayed the specific energy function as a surface in three dimensions for rectangular cross sections. For the first time, the specific energy function is also visualized in three dimensions for rectangular and trapezoidal cross sections as well as a compound channel cross sections, revealing unexpected features. Above all, this study is particularly meaningful in expressing alternate depth and critical water depth in an effective way that only a few researchers have tried to express before.