Constant Flow Discharge Research Articles

Prediction of Soil Erosion Using 3D Point Scans and Acoustic Emissions

Over half of the approximately 12,000 earthen watershed dams sponsored by the USDA have exceeded their planned 50-year service life. Age, land use changes, extreme weather events, structural deterioration, and sedimentation filling flood pools pose increased risks of dam incidents and potential failures. Among various mechanisms leading to integrity issues, soil erosion is of particular concern due to its potential to occur with little warning. The objective of this research is to determine if soil erosion can be predicted using acoustic emissions. A simulated dam overtopping experiment was replicated in a test flume with dimensions of 0.61 m by 4.27 m (2 ft. by 14 ft.) with a 13.7% slope and a 0.15 m (6 in) layer of inorganic clay (USCS CL) compacted at 17.4% moisture content. A constant flow discharge of 0.07 m3/s (2.37 cfs) was applied to induce erosion. The test was performed until complete failure of the test section occurred. Throughout the experiment, a sonar radar, a 3D scanning total station, and an accelerometer were used to monitor the water level, erosion levels, and vibrations, respectively. The frequency analysis of the water-induced vibrations was compared to measured erosion volumes to determine if in situ vibrations can predict erosion. The results revealed a linear relationship between erosion volume and time, with noticeable changes in the frequency domains as erosion progressed. The outcomes of this research have the potential to provide real-time insights into the integrity of earthen dams concerning erosion, offering a valuable tool for monitoring and maintenance.

On thermodynamics and heat and mass transfer aspects of CH4 adsorption onto coconut shell-based carbonaceous material

The current study investigates the equilibrium methane (CH4) adsorption capacity and the adsorption kinetics of a locally produced coconut shell-derived activated carbon (AC CARB 6X12 60) for pressure and temperatures ranging from 0 to 55 bar and -20 to 70 °C, respectively. The adsorption isotherms and kinetics are determined using an in-house developed adsorption test rig. A maximum methane adsorption uptake of 0.140 kg/kg is obtained at -20 °C and 40 bar pressure. The adsorption equilibrium isotherm data are fitted using Toth, Dubinin-Astakhov (DA), and Modified-DA isotherm models. Afterwards, the kinetics study is done considering pseudo first order, second order, Elovich, and intra-particle diffusion models. In continuation, based on the DA isotherm model, Clausius Clapeyron relation, and Maxwell's relations, the expressions for the crucial thermodynamic parameter of adsorbed phase, i.e., isosteric heat of adsorption, specific heat capacity, enthalpy, and entropy is derived, and same is estimated using DA isotherm parameters. Additionally, the activated carbon's thermophysical properties (i.e., thermal conductivity, thermal diffusivity, and specific heat) are determined using the TPS 2500 S analyzer, which works on the hot-disk principle. Using the most suitable isotherm (DA) and kinetic model (pseudo second order), heat and mass transfer analysis is carried out on novel reactor configuration with an external cooling jacket, double row of cooling pipes with external longitudinal fins for methane storage using a 3D transient model in Comsol Multiphysics. The charge characteristics are studied for gas charging pressure varying from 1 to 50 bar and cooling fluid temperature of -20 to 70 °C. Iso-concentration contours are plotted to identify the pressure-temperature combination resulting in identical storage capacity (i.e., including both gaseous and adsorbed phases). Further simulations are carried out for constant pressure charging and constant flow discharge conditions to expound upon the effects of the dormancy period, gas charging pressure, and cooling/heating fluid temperature. 14% improvement in total discharge amount is obtained with a dormancy period between charging and discharging compared to no dormancy case.

First Principles‐Based Approach for 3D Scour Processes Under Variable Jet Discharge

AbstractScour processes caused by plunging jets are particularly important in hydraulic engineering because of the connected risk of structural failure. Therefore, many investigations have been conducted on this topic, focusing on jet‐induced scour under constant flow discharge (i.e., steady case). Yet, to the best of the authors' knowledge, no studies have analyzed the scour mechanism under variable jet discharge (i.e., unsteady case) and clear‐water conditions. Following recent theoretical advancements on scour phenomena for steady cases based on the phenomenological theory of turbulence, we address in this study the general validity of such an approach for time‐dependent (i.e., unsteady) jet inflow conditions, in non‐cohesive soils. Results show that scour evolution is consistent with that obtained for steady jet flows. In particular, they confirm the existence of two distinct phases—developing and developed—and indicate that the transition time between the two phases does not depend on the jet inflow characteristics. Once again, this study confirms that the phenomenological theory of turbulence is a valid tool for all jet‐driven scour problems.

Experiments on restoring alluvial cover using gravel augmentation in a variable width channel with irregular meanders

In partially-alluvial channels, an understanding of cover formation over a non-alluvial substrate is necessary for effective river management or restoration. Urban rivers, for example, are often sediment starved such that the underlying substrate may be exposed. Few experiments have investigated cover development in meandering channels, particularly where width and meander geometry are irregular as is often the case for partially alluvial channels. The purpose of this work is to support the development of sediment augmentation strategies to mitigate channel degradation and restore alluvial cover. The experiments also provide new insight into the impact of sediment supply rates on alluvial cover dynamics in variable-width channels. Under constant flow discharge and a continuous supply of sediment, sediment disperses downstream of the feed location and cover develops in a fragmented fashion. Cover initiation occurs downstream of bend apexes and develops as a series of discrete fixed bars whose morphology differs as a function of bend geometry and channel width. Cover expands and bars merge with time under steady sediment supply and discharge, eventually thickening to an equilibrium state in which sediment supply and output are approximately balanced. Higher sediment supply rates result in more extensive and thicker cover at equilibrium, including cover expanding into the cross-overs between the main bars. Coarse and fine fractions of the sediment supply are preferentially retained in the cover sediment because of fine particle deposition on bar tops and burial of initial coarse deposits. Models of areal cover with feed rate and cover thickness are proposed and compared with other studies. More experimentation is needed, but augmentation of alluvial gravel cover is a feasible approach to maintaining a sediment balance in partially-alluvial channels and for developing mobile alluvial cover in engineered channels.

Overflow characteristics of streamlined weirs based on model experimentation

Weirs are a type of hydraulic structures that are used in water supply systems and irrigation networks for different purposes. These structures are categorized as different types and must be selected in respect to the hydraulic conditions to satisfy all the objectives of a project. The present study subjects to investigate the hydraulic characteristics of flow over the streamlined weirs, based on model experimentation. The streamlined weirs are a special type of weirs, designed based on the airfoil theory. These weirs have some merits compared to the other types of weirs. They have high discharge coefficient, more stability and less fluctuations of water free surface. According to the objectives of the present study, an experimental investigation was performed, using different experimental models of the streamlined weirs, designed according to the Joukowsky transform function. Experimental results inferred that for a constant flow discharge, the upstream flow heads over the streamlined weirs with different relative eccentricities are almost constant, showing an approximately constant discharge coefficient by the variation of the relative eccentricities. Furthermore, adding a downstream sloped face does not change the flow discharge coefficient. However, increasing the weir height, results in the increase of the flow head and the decrease of the flow discharge coefficient, especially, for the higher heads and the lower relative eccentricities.

Simulation of free surface flow over the streamlined weirs

The streamlined weirs are a special type of weirs, designed on the basis of airfoil theory. Because of their particular design, they have some merits compared to the other types of weirs, such as; high discharge coefficient, more stability of overflow and less fluctuations of water free surface. In the present study, a numerical simulation performed using an open source software namely, OpenFOAM, to give details about the flow structure over, up- and downstream of these weirs. Also, an experimentation setup was devised to evaluate the numerical results and determine the best numerical model. Analyzing the results of different turbulence models including; standard k-ε, realizable k-ε, RNG k-ε, k-ω SST, and Reynolds stress LRR, indicated that all the aforementioned models accurately estimate the flow field and hydraulic parameters. However, the k-ω SST model gives more accurate results, very close to the experimental data especially for the Reynolds stresses. Accordingly, the k-ω SST turbulence model was chosen as the best turbulence model for analyzing the flow over the streamlined weirs. Numerical results for different relative eccentricities show that, by increasing the relative eccentricity, the flow velocity over the crest of the weirs increases and accordingly the pressure in such section decreases. For a constant flow discharge upstream of different types of the streamlined weirs, the lowest bed pressure and the most probable potential of cavitation belongs to a circular-crested weir (a streamlined weir with a relative eccentricity of unity). Furthermore, the greatest bed shear stresses and the compressive forces occur downstream of the circular-crested weir. Thus, downstream of a circular-crested weir is responsible for larger potential of bed erosion. This is partly due to the formation of shock waves, reduction of the flow depth, and enhancement of the flow velocity downstream of a circular-crested weir. Moreover, the lowest bed shear stresses were observed upstream of the circular-crested weir. Therefore, upstream of a circular-crested weir shows the greatest potential of sedimentation. Finally, applying the streamlined weirs with an appropriate curvature, diminishes the unfavorable flow conditions, as observed for the circular-crested weir, being the safer and economic hydraulic structures.

Experimental Study of the Effects of Flow Discharge, Diameter, and Depth on Shear Stress in a Rectangular Channel with Rigid Unsubmerged Vegetation

Abstract Shear stress is one of the most critical parameters in hydraulic and coastal engineering, which is often measured indirectly. Since there is no instrument to measure this parameter directly and given that it is usually calculated by measuring other parameters such as velocity and pressure and using some equations, shear stress measurement is often accompanied with large measurement errors. In this study, a new technique and direct measurement using physical modeling in a hydraulic knife-edge flume and load cell were employed to measure the shear stress in a rectangular channel with rigid unsubmerged vegetation with Dv= 20, 25, and 32mm in Q=25 and 30 Lit/S and y=10, 12, 17, and 20 cm. The results indicate that the shear stress and the dimensionless τ 0 τ {{{\tau _0}} \over \tau } ratio decrease in a constant flow discharge with increasing the flow depth. It was also shown that the shear stress would be enhanced with an increase in vegetation diameter due to increasing vegetation density against flow. According to dimensionless ratios of τ 0 τ {{{\tau _0}} \over \tau } and D v y {{{D_v}} \over y} in the graphs and considering the trend lines with appropriate correlation coefficients, some equations were presented to calculate the shear stress in the concerned range.

Variations of bed elevations due to turbulence around submerged cylinder in sand beds

This paper presents the spatio-temporal variations in bed elevations and the near-bed turbulence statistics over the deformed bed generated around the submerged cylindrical piers embedded vertically on loose sediment bed at a constant flow discharge. Experiments were carried out in a laboratory flume for three blockage ratios in the range of 0.04–0.06 using three different sizes of submerged cylinders individually placed vertically at the centerline of the flume. Clear-water experimental conditions were maintained over the smooth sediment bed surface with a constant flow discharge (\(Q = 0.015\,{\rm m}^3/{\rm sec}\)), thereby giving three different cylinder Reynolds numbers \(Re_{D_c} = \frac{U_mD_c}{\nu }\) (=10200, 12750, 15300) away from the cylinder locations, where \(U_m\) is the maximum mean velocity, \(D_c\) is the cylinder diameter and \(\nu\) is the kinematic viscosity of fluid. Instantaneous sand bed elevations around the cylinders were recorded using a SeaTek 5MHz ultrasonic ranging system of net 24 transducers to estimate bed form migration, and the near-bed velocity data at transducer locations over the stable deformed bed around the pier-like structures were collected using down-looking three-dimensional (3D) Micro-acoustic Doppler velocimeter to estimate the bottom Reynolds shear stresses and the contributions of bursting events to the dominant shear stress component. The flow perturbation generated due to relatively lower flow blockage ratio favored to achieve the stable bed condition more rapidly than the others, and larger upstream scour-depth and deformed areas were noticed for greater flow blockage ratio due to larger cylinder diameter. For larger blockage ratio in the upstream of scour-hole near the bed, occurrences of probabilities of both boundary-ward interactions (Q1 and Q3) were the dominant; whereas in the downstream of the scoured region, occurrences of probabilities of second and third quadrant events (Q2 and Q4) were dominant. On the other hand, for the lower blockage ratio, quadrant (Q2) was dominant over Q4 in the downstream of scour-hole, and in the upstream of scour-hole, quadrant Q4 was the dominant.

Development of mesh-free particle technique for simulation of non-hydrostatic free surface flow

Up to now, the ability of mesh free methods has been demonstrated by simulating various open channel flows; however, the prediction of non-hydrostatic pressure variation due to change in flow direction has not been studied. For purpose of illustration, flow over flip buckets is considered in the present paper. A novel feature of this paper is employing new technique for refining the solid boundary particles to reduce pressure fluctuations in computation. The presented technique is very efficient computationally since only the bed solid particles are refined. To simulate the curve path and geometry of the bucket accurately a gradually changing particle size technique is used for the bucket invert. A new method is also used to impose the constant flow discharge on the inlet without considering any additional particles to enter the flow domain. Free surface elevation along the bucket, lower and upper takeoff angles and trajectory of the jet, dynamic pressure distribution and location of maximum pressure along the flip bucket were then calculated in different approach Froude numbers and ratio of flow depth to bucket radius of curvature. Comparison of the numerical model with experimental data and results of empirical equations showed a good agreement. These results show the ability of the present developed model to simulate non-hydrostatic free surface flows particularly where complex geometries are involved.

Spatial width oscillations in meandering rivers at equilibrium

In canaliform rivers channel width at bankfull stage is fairly uniform though, at bend apexes, it is typically smaller than at crossings. Conversely, in sinuous point bar rivers bankfull width peaks at bend apexes. Why? Is there any mechanistic constraint that forces this different behavior? We provide an answer to these questions investigating how bankfull width must vary in a sequence of sine‐generated meanders in order for the constraints of equilibrium (constant flow discharge and sediment flux) to be satisfied. With the help of a 3‐D fully nonlinear analytical model of flow and bed topography in meandering rivers with variable width, we show that, in a meandering channel characterized by a constant longitudinal free‐surface slope, the equilibrium width thus obtained oscillates with a frequency twice the frequency of channel curvature and experiences the maximum width close to inflection points. This pattern is typically observed in canaliform rivers. We then show that a similar pattern is observed in sinuous point bar rivers, provided the hydrodynamic width (width of the free surface) is replaced by the active width, namely the width of the portion of the cross section where transport occurs at formative conditions. Theoretical results are substantiated by a satisfactory comparison with field observations referring to the Mississippi River (United States) and to the Bollin River (United Kingdom).

Transport rate-based model for overland flow and solute transport: Parameter estimation and process simulation

A one-dimensional mathematical model, termed a transport rate-based model, is developed for solute transport over infiltrating soil slopes under constant rainfall and declining sources. The model is comprised of (1) the kinematic-wave equation for overland flow, (2) a transport rate-based advection equation for overland solute transport, (3) a moment-based method for estimation of the parameters involved in the flow and solute transport equations, and (4) a semi-Lagrangian algorithm for numerical solution of the solute transport equation. Data from a single soil flume experiment under constant rainfall established the proof-of-concept for this new model. Sodium chloride was applied to the soil surface to simulate the presence of a declining diffuse pollutant. The parameters involved in the flow equation were found to take on the values that correspond to turbulent flow. With these turbulent flow parameters the simulated hydrograph displayed an initial rising limb, followed by a constant flow discharge. The profile of solute concentration exhibits a steep receding limb transitioning into an elongated tail. The solute transport rate follows a non-Gaussian distribution that does not appear to have been derived before. These theoretical hydrographs and pollutographs are in good agreement with those measured in laboratory, demonstrating the laboratory proof-of-concept for the transport rate-based model on soil and pavement blocks.

Fractional Kinetic Model for First Flush of Stormwater Pollutants

By generalizing the urban ground as a fractal surface and revising the classical Fick’s formula as a law of dispersion with a fractional-order derivative, a fractional kinetic model is developed for simulation of the first flush phenomenon of urban stormwater pollutants. The model is comprised of (1) a fractional dispersion-advection equation (FADE); (2) the kinematic-wave overland flow equation; and (3) methods for numerical solution of the equations. A split-operator method is proposed for numerical solution of the FADE by means of a newly presented F.3 finite-difference scheme for fractional partial differential equations. The kinematic-wave overland flow equation is solved using the Lax–Wendroff explicit scheme. Under a constant rainstorm the hydrograph displays an initial rising limb followed by a constant flow discharge. The pollutograph exhibits a steep receding limb (the first flush), followed by a long stretched tail (heavy tail process). The agreement between simulated and measured dispersion characteristics is found to be good, demonstrating that the fractional kinetic model is capable of accurately predicting the characteristics of the first flush phenomenon.

Concentrated flow erosion rates as affected by rock fragment cover and initial soil moisture content

Concentrated flow experiments using a small hydraulic flume and a constant flow discharge and bed slope have been conducted in order to investigate the effects of rock fragment cover (Rc) on sediment yield for an initially wet and an initially air-dry loamy topsoil. The experimental results indicate that Rc reduces concentrated flow erosion rates ( E) in an exponential way (i.e., E= e − bRc ), which is similar to previously reported relations for other water erosion processes such as interrill erosion and sheet-rill erosion measured on runoff plots. The decay rate ( b) of this exponential relationship increased throughout the experiments because of scour-hole development and bed armouring. The concentrated flow erosion rates and b-values also depend on the initial moisture content of the topsoil. Depending on Rc, mean concentrated flow erosion rates were 20% to 65% less on initially wet compared to initially air-dry topsoils. The mean value for b was 0.032 for the initially wet, but only 0.017 for the initially air-dry topsoil, indicating that a rock fragment cover is less efficient in reducing concentrated flow erosion rates when the topsoil is initially air-dry than when it is initially wet. The results help explain the data scatter in reported relationships between Rc and interrill–rill erosion rates. They also indicate that a given surface rock fragment cover will offer more protection to wet topsoils than to dry topsoils, which are very common in Mediterranean environments. Event-based water erosion models should incorporate effects of antecedent soil moisture content as well as those of Rc on concentrated flow erosion rates.

Origin of cross-laminas in a laboratory experiment

A quantitative explanation is cited for the origin of the cross-laminated structure of a microdelta deposited in a laboratory flume under conditions of constant flow discharge and sediment input. The structure originated when the sediment load carried over the front of the delta was differentiated into finer and coarser size fractions by hydrodynamic sorting processes. Detailed sampling of the sediment load for grain size distributions demonstrated that the most important sorting process was selective transport and deposition related to differential settling velocity. The cross-laminas composed of the coarser grain sizes were produced by the downslope transfer of material from the upper foreset slope of the delta. This material was primarily of bed-load origin. On the other hand, the cross-laminas composed of the finer grain sizes were produced by the fallout of suspended sediment onto the middle and lower parts of the foreset slope. This material was derived mostly from the sediment carried in suspension by the heavy fluid layer flowing along the stream bed. It was possible, therefore, to correlate the stratified nature of the foreset with the density-stratified nature of the heavy fluid layer. The cross-laminated structure of the deposit wras quite distinct even though the size differential between the fine and coarse layers was only 0.05mm. Based on the results of this paper, a possible procedure is outlined for predicting the size differential between the fine and coarse laminas of the foreset for other conditions of experimentation. Specifically, the procedure entails a reconstruction of the inferred path lines of the particles settling out in the flow transition and a calculation of the rate of decrease of median grain size in the downstream direction.