Flume Slope Research Articles

Assessment of Debris Flow Impact Based on Experimental Analysis along a Deposition Area

Debris flow is a devastating phenomenon that happens in hilly and mountainous regions and has a serious impact on affected areas. It causes casualties and serious damage to the environment and society. Therefore, a susceptible assessment is necessary to prevent, mitigate, and raise awareness of the impact of debris flows. This paper focuses on evaluating the deposition area along the deposition board. The methodology involved an experiment on a physical model by demonstrating the debris flow based on the steepness of the flume slope at 15°, 20°, and 25° angles. The limestone particles with a total volume of 2.5 × 106 mm3 acted as debris and were released with water from the tank to the deposition board with an area of 10 × 105 mm2. The volume, area, and length of particle distribution carried from the flume to the deposition board were then determined. Based on the experimental results, the deposition board is covered with particles of about 696.19 × 103 mm3, 748.29 × 103 mm3, and 505.19 × 103 mm3 volume for each 15°, 20°, and 25° angle, respectively. In actual situations, debris flow is capable of causing significant risk to the affected area. This study can be deemed useful for a risk assessment approach, to help develop guidelines, and to mitigate the regions where debris flows are most probable to occur.

Control and Interception Characteristics of the Debris-Flow Flexible Net Barrier Based on Orthogonal Design

As a debris-flow control and mitigation countermeasure, flexible net barriers can effectively mitigate debris flows. The control and interception characteristics of flexible net barrier play an important role in engineering design. Many influencing factors exist in debris-flow flexible net barrier control and interception processes. In order to explore the most important factors, a flume-based experimental study was carried out by selecting the four main factors, i.e., the flume slope, debris flow bulk density, net barrier interval and relative volume. The purpose of the study is to analyze the influencing degree of the four factors. Moreover, the debris-flow interception ratio, blocking ratio, velocity reduction ratio and bulk density attenuation ratio are taken as the evaluation index. Based on the theory of orthogonal experimental design, the experiment results were analyzed in detail by range analysis and variance analysis. The research results indicated the following: in regard to the interception ratio, blocking ratio, and velocity reduction ratio, the net barrier interval exerted the most notable impact, followed by the bulk density. In regard to the bulk density attenuation ratio, the flume slope and bulk density were the first and second most important influencing factors, respectively. The form of interception ratio with maximum value was as follows: the flume slope was 9°, the net barrier interval was 18 mm, the bulk density was 21 kN/m3 and the relative volume was 2/3. The form of blocking ratio with minimum value was as follows: the flume slope was 6°, the net barrier interval was 50 mm, the bulk density was 12 kN/m3 and the relative volume was 1/2. The form of velocity reduction ratio with maximum value was as follows: the flume slope was 12°, the net barrier interval was 18 mm, the bulk density was 17 kN/m3 and the relative volume was 1. The form of bulk density attenuation ratio with maximum value was as follows: the flume slope was 12°, the net barrier interval was 30 mm, the bulk density was 17 kN/m3 and the relative volume was 1/3.

Influence of Water Depth and Slope on Roughness—Experiments and Roughness Approach for Rain-on-Grid Modeling

Two-dimensional (2D) models have become a well-established tool for channel flow, as well as rain-induced overland flow simulations. In channel flow simulations, slopes are usually less than a few percent and water depths are over several meters, while overland flow simulations show steep slopes and flow of a few centimeters. Despite these discrepancies, modelers transfer roughness coefficients, validated for channel flow, to overland flow. One purpose of this study is to verify whether roughness values from the literature are also valid for overland flow simulations. Laboratory experiments with different degrees of bed roughness, various discharges and a range of experimental flume slopes were carried out. For a given discharge, water depth was measured, and bed roughness was derived. Experimental results reveal that roughness shows no clear dependence on slope but is strongly dependent on water depth for vegetated surfaces. To verify the influence of different roughness approaches, they were implemented in a 2D model. A comparison of different simulation results indicates differences in the hydrograph. Here, consideration of water depth-related roughness coefficients leads to retention and translation effects. With the results of this study, modelers may enhance the precision of the hydraulic component in overland flow simulations.

Estimating flow resistance in steep slope rills

AbstractRecent research recognized that the slope of 18% can be used to distinguish between the ‘gentle slope’ case and that of ‘steep slope’ for the detected differences in hydraulic variables (flow depth, velocity, Reynolds number, Froude number) and those representatives of sediment transport (flow transport capacity, actual sediment load). In this paper, using previous measurements carried out in mobile bed rills and flume experiments characterized by steep slopes (i.e., slope greater than or equal to 18%), a theoretical rill flow resistance equation to estimate the Darcy‐Weisbach friction factor is tested. The main aim is to deduce a relationship between the velocity profile parameter Γ, the channel slope, the Reynolds number, the Froude number and the textural classes using a data base characterized by a wide range of hydraulic conditions, plot or flume slope (18%–84%) and textural classes (clay ranging from 3% to 71%). The obtained relationship is also tested using 47 experimental runs carried out in the present investigation with mobile bed rills incised in a 18%—sloping plot with a clay loam soil and literature data. The analysis demonstrated that: (1) the soil texture affects the estimate of the Γ parameter and the theoretical flow resistance law (Equation 25), (2) the proposed Equation (25) fits well the independent measurements of the testing data base, (3) the estimate of the Darcy‐Weisbach friction factor is affected by the soil particle detachability and transportability and (4) the Darcy‐Weisbach friction factor is linearly related to the rill slope.

Morphology, Bedload, and Sorting Process Variability in Response to Lateral Confinement: Results From Physical Models of Gravel‐bed Rivers

This paper uses flume experiments to investigate the influence of lateral width confinement on channel morphology, sediment sorting, and bedload transport. Three runs of about 60 hr were carried out under constant feeding rate equal to 0.6 l/s and 8 g/s, with a bimodal mixture of natural sediments, a fixed flume slope of 3%, and width imposed by lateral walls from 0.12 to 0.50 m in order to model three different flow confinement configurations. Despite the three runs transporting at the same rate on average, they presented different gravel‐bed river morphologies and different degrees of bed complexity. The three runs also presented differences in bedload transport rate fluctuations associated with different magnitude and mechanisms of bed storage and release of sediments. The intermediate width configuration (Run 2) was found to have a minimum storage and release of sediments compared with both the wider configuration (Run 1) and the narrower configuration (Run 3). Runs 1 and 3 were characterized by a significant storage and release of sediments resulting in a highly fluctuating bedload transport rate; however, while Run 1 (braiding morphology) stored and released sediments through lateral deposits and bed variations with planimetric sorting, Run 3 (single‐thread channel) stored and released sediments through variations in bed elevation accompanied by vertical sorting. We extrapolated this concept to the full set of gravel‐bed river morphologies, thus speculating about the channel morphology for optimal sediment transfer.

A flume experiment study of energy lose at downstream of a sluice gate

A sluice gate is a controllable barrier that controlling the elevation of the water at the channel. Generally, energy change occurs at the upstream and downstream of watergate, caused by the impact of the water flow at watergate upstream. This study aims to analyze the energy change at Watergate and to compare the value of energy change that occurs at the channel with or without sediment. This research was carried out by the Civil Engineering Hydraulics Laboratory of the Faculty of Engineering, Hasanuddin University, which runs from December 2018 to March 2019. In this research, we use some variables that are channel bed condition, flume slope, debit, and watergate openings. The result of this research shows that debit and watergate openings really affect the value of the energy change, while the flume slope is not really affected it. The energy change that occurs at the flume without sediment is bigger than the energy change that occurs at the flume with sediment in it.

Effect of the slope of flume bed to the debris potential flow

This article aims to determine the effect of the basic flume slope to the potential flow of debris flow. This article discusses the combination of open check dam type (beam type) placed at the top and the closed check dam type placed at the bottom with variation of the distance between the checks of dam in a flume with the size used in the experiment that is 30 cm x 32.8 cm x 1200 cm with a slope of 10°. The composition of the sediment used is type D50. The results of this study using three types of base flume slope are the greater the slope of the base flume will result in a greater debris flow on the condition without wood and on conditions with wood. The larger the slope, the greater the sediment and wood that passes from the check dam series. The smaller the base slope of the flume, the larger the timber being retained on the open check dam.

Experimental bedforms by saline density currents

Abstract Bedforms are sedimentary features that can be generated on the seafloor by the interaction between density currents and mobile beds. Developing knowledge about the hydraulic and sedimentary processes involved during these events is in the interest of research groups and oil companies. Because of the magnitude of the density currents in its natural environment and the challenge in collecting data, studies in laboratory are of great value. We present results of 29 experiments focusing in the bedform development generated by saline currents, testing two different sediment types and three grain sizes: melamine (245 µm-plastic) and sands (206 and 485 µm). We analyzed the current velocity and fractional density profiles as well as pictures taken during and after each run. Results have showed classical velocity and concentration profiles, for 8 subcritical and 21 supercritical currents, with densimetric Froude numbers (Frd) between 0.5 and 2.2. Some correlations were identified, such as the decrease of the velocity peak height and increase in the mean velocity (with consequent reduction of the current thickness), due to an increase of the concentration and/or flume slope. The occurrence of bedforms was more likely for high discharge and concentration rates of current density, which directly influence the Frd. Bedforms were classified according to the shear stresses values applied by the current to the bed, resulting in the generation of lower plane bed, ripples and dunes. Dunes and ripples were observed in supercritical flow conditions, which is a hydraulic scenario of bedforms generation not predicted by fluvial models. Thus, this study demonstrated the existence of differences in generation and, consequently, the classification approach for density current bedforms, compared to those generated by river flows. To this fact is attributed the hydrodynamic (velocity and concentration profiles) and sediment transport differences between fluvial flows and density currents. Further studies may be carried out in order to constructing new concepts of bedforms generation by density currents.

Development of Debris Flow Impact Force Models Based on Flume Experiments for Design Criteria of Soil Erosion Control Dam

Soil erosion control dams are widely used as part of measures to reduce damage caused by debris flow all over the world. Engineering considerations are needed for proper design of erosion control dams, but in the Republic of Korea, the impact force of debris flow is not fully reflected in the current design criteria of the dam. Against this backdrop, this study was conducted to estimate the impact force of debris flow for the practical purpose of designing erosion control dam. Simulated flume experiments were performed to develop the relationship to estimate the flow velocity as well as the impact force of debris flow. Experimental results showed that increases both in sediment mixture volume and flume slope gradient led to an increase in flow velocity. Especially, it was found that as clay content increased gradually, the flume slope gradient had greater impact on the increase of flow velocity. Also, it was proved that the impact force of debris flow was well fitted to the hydrodynamic model as it showed linear correlation with the flow velocity. Then, the debris‐flow velocity model was established based on the factor related to the debris‐flow velocity. Finally, the dynamic model to estimate the impact force of debris flow was introduced utilizing correlations between the established debris‐flow velocity model and Froude number. Both models which were developed with using statistically significant watershed characteristics succeeded in explaining the experiment results in a more accurate way compared to existing models. Therefore, it is highly expected that these models can be fully utilized to estimate impact force of debris flow which will be required to design erosion control dams in practical use through overcoming their identified limitations.

Flow measurement using circular portable flume

The circular portable flume is a simple device to measure discharge in circular drainage networks. Since the unit can be easily installed and removed, it is helpful in water distribution measurement and management. First in this paper the available studies are reviewed for highlighting the effect of both the contraction ratio and the flume slope on the stage-discharge relationship. Then the Buckingham's Theorem of the dimensional analysis and the self-similarity theory are used to deduce the stage-discharge curve of the circular flume. The new theoretical stage-discharge equation is calibrated by the literature available experimental data and those obtained in this experimental investigation for a wide range of the contraction ratios. The developed analysis suggested that the contraction ratio, which was neglected so far from the functional relationship, would significantly affect the stage-discharge curve. Finally, the effect of the flume longitudinal slope on the stage-discharge equation is tested by the experimental data obtained in this study and some other available literature experimental data.

Hydrodynamic Characteristics of the Formation Processes for Non-Homogeneous Debris-Flow

Non-homogeneous debris flows are characterized by a wide grain size gradation, high volumetric weight and sediments not uniformly distributed along the vertical direction of the flow depth. These flows usually occur in the southwestern mountainous area of China during the rainy season, causing tangible and non-tangible damages; therefore, it is crucial to study their dynamic characteristics. An experimental campaign was conducted to replicate three processes typical of debris flows: (i) formation; (ii) propagation; and (iii) accumulation. Different flow rates, soil composition and flume slopes were applied. Multiple experimental parameters were quantified for each test conducted such as pore water pressure and velocity and a series of regression analyses were used to determine the relative impact of each experimental variable on these recorded parameters. The results showed that the flowrate and the vertical grading coefficient associated with the soil composition have the maximum and the minimum influence on the formation of debris flows and propagation velocities measured, respectively. This result is significant and needs to be considered when planning or designing control measures to reduce the impacts of debris flows.

Experimental observations on sorting patterns of heterogeneous sediment mixtures in low constrained flows

Field and laboratory investigations indicate that gravel bed rivers with bimodal grain size distribution and low lateral confinement, such as in the case of braided or multi-channel rivers, can present simultaneously active channel variations, both in the planimetric and altimetric directions, together with planimetric and vertical sorting. Such aspects were reproduced in new flume experiments considering three flow confinements with characteristic aspect ratios from about 80 to 5. Three long runs of about 60 hours were carried out under constant feeding rate conditions, with a bimodal mixture of natural sediments, a fixed flume slope of 3.18 %, and width imposed by lateral walls from 0.50 m to 0.12 m. We present here the results obtained with the first run, with a width of 0.5 m. We observed fluctuations of bed surface granulometric composition, bed slope, and outlet solid discharge; each of which with its own periodicity. In particular, the rearrangement of the bed surface texture was rapid. Cyclic bed states were observed: a stage of coarsening and aggradation corresponding to low values of outlet solid discharge; a stage of fining and degradation concomitant to high values of transport rate. The other two on-going runs (narrower configurations) aim at investigate the effect of lateral confinement on the morphodynamics of the system.

An experimental study on controlling post-earthquake debris flows using slit dams

Post-earthquake debris flows often break out in groups frequently, which are usually caused by the abundant loose solid materials that produced by earthquake. Slit dams represent a practical and effective kind of countermeasure for controlling the post-earthquake debris flow. Flume experiments were carried out to study the interaction mechanism and the effect of slit dams on the post-earthquake debris flows. The results showed that affected by the slit dams, some certain types of deposits formed on the upstream. The steeper the flume slope, as well as the greater the width and the density of slits, the easier the lateral deposit became “V” shaped. Otherwise, the lateral deposit was more likely to be “–‒” shaped. When the flume slopes were 12°, 16° and 20°, the profiles of the deposits would be long-shallow type, short-thick type and short-shallow type, respectively. The slope of the deposition first decreases and then increases with the flume slope increasing within a certain range. The slit dam can trap the coarse sand and discharge the fine sand. The maximum attenuation rate can reach 44.4%. The effect of this capacity gradually weakens as the flume slope is increased. When the width or the density of slits is smaller, the greater the rate of decrease in peak sand discharge and the greater the effect of peak cutting will be. The reduction in the sediment storage rate is likely due to the increase in the width and the density of the slits. With the increase in flume slope, the sediment storage rate first increases, then decreases, which reaches a maximum value when the flume slope is 16°.

Experimental study on the energy dissipation characteristics of debris flow deceleration baffles

Debris flow can cause serious damages to roads, bridges, buildings and other infrastructures. Arranging several rows of deceleration baffles in the flow path can reduce the flow velocity and ensure better protection of life and property. In debris flow prevention projects, deceleration baffles can effectively reduce the erosion of the debris flow and prolong the running time of the drainage channel. This study investigated the degree to which a 6 m long flume and three rows of deceleration baffles reduce the debris flow velocity and affect the energy dissipation characteristics. The influential variables include channel slope, debris flow density, and spacing between baffle rows. The experimental results demonstrated that the typical flow pattern was a sudden increase in flow depth and vertical proliferation when debris flow flows through the baffles. Strong turbulence between debris flow and baffles can contribute to energy dissipation and decrease the kinematic velocity considerably. The results showed that the reduction ratio of velocity increased with the increase in debris flow density, channel slope and spacing between rows. Tests phenomena also indicated that debris flow density has significant influence on the mobility and deposition characteristic of debris flow. The deposit amount first increased then decreased when the flow density rises, and the deposit amount of debris flow density of 1500 kg/m3 reached the maximum when the experimental flume slope is 12°.

An analysis of the supply process of loose materials to mountainous rivers and gullies as a result of dry debris avalanches

A dry debris avalanche will produce different volumes of colluviums or depositions (loose materials), which can have a significant impact on mountainous rivers or gullies. The loose material supply process caused by a debris avalanche is an important issue for understanding secondary disasters that form via the coupling of water flow and loose materials. Two flumes were designed for laboratory tests of the loose materials supply process to rivers/gullies, and the related impact factors were analyzed. Experimental results show that the supply of loose materials is a continuous process that directly relates to the avalanche’s mass movement processes. The sliding masses with smaller particle sizes are more sensitive to the flume slope and exhibited a longer supply time. The time-consuming for the debris avalanche travel in the flume decreased with the increasing particle size (such as flume B, time-consuming is decreased 0.2 s when the particle size increased from <1.0 to 20–60 mm), landslide volume and flume slope (flume A, consuming 1.6–2.1 s when flume slope is 29° decreased to consuming 1.3–1.5 s when flume slope is 41°), which means the increasing mobility of loose materials. The total supply time increased with the increasing landslide volume or decreasing particle size and flume slope. An empirical model for the process is presented based on numerous laboratory tests and numerical simulations, which can successfully describe the supply process for loose materials to a river/gully. The supply process of loose materials to mountainous gully from a dry debris avalanche is controlled by the material compositions of sliding masses, topographical conditions, landslide volume and bed friction, where large-volume debris avalanches that occur in mountainous river regions are more likely to obstruct the river flow and form a landslide-dammed lake.

Experiment on temporal variation of bed load transport in response to changes in sediment supply in streams

AbstractA flume experiment was conducted to study channel adjustment to episodic sediment supply in mountain streams. The bulk sediment used for the bed and feed included grain sizes 0.5–64 mm with geometric mean D of 5.7 mm. Water discharge was held constant for 40 h, and 300 kg of sediment was supplied through a range of scenarios. Bed slope, sediment storage, sediment transport, and bed surface texture responded to sediment supply. During the first of seven runs, bed slope decreased from 0.022 m m (flume slope) to 0.018 m m due to sediment starvation. Bed slope increased beginning in the second run as the bed aggraded due to preferential storage of grains &gt;8 mm. Transport rate and bed‐surface particle size were significantly affected by magnitude‐frequency of sediment feed. Under constant feed, transport rate increased gradually and D ranged between 12 and 15 mm. Instead, sediment pulses caused a pronounced increase in sediment transport rate and surface fining, trends that were inverted as sediment evacuated. At the run scale, sediment transport and storage behaved as with constant feed if pulse relaxation time exceeded time between pulses. The increase in transport rate and surface fining were proportional to pulse size. After the 300 kg pulse, transport rate reached and D was &lt;10 mm. After 75 kg pulses, transport rate reached and D was &gt;12 mm. Textural differences on the initial bed surface influenced the patterns of sediment transport. Channel adjustment was controlled by magnitude‐frequency of sediment feed and not by total feed.

Hotelling의 T-square 통계량을 이용한 강우유발 사면붕괴 예측

A new technique is presented to detect unstable slope behavior, based on Hotelling`s T2 analysis of pore pressure and water content obtained during flume tests using granitic and gneissic weathered soils. Three sets of pore pressure-water content values were simultaneously obtained during each test, and T2 statistics at the 90.0% and 95.0% confidence levels were calculated based on the correlations between values. The results show that unsuccessful detection of some local failures of the flume slope depended on the sensor position. In the case of global slope failures, anomalous behavior was detected between several hundred and several thousand seconds before the event as T2 statistics exceeded the confidence interval 90%. Hotelling`s T2 analysis provides a single control criterion because it enables correlations between diverse measured values within the same slope; the criterion also includes stepwise criteria for a forecasting and warning system based on confidence levels.

Factors influencing the formation of shallow landslides in the Boston Mountains of northwest Arkansas, USA

Slope failures cause billions of dollars of damage annually and put human lives at risk. This study employed field measurements and observations to provide the framework for laboratory simulations to investigate the effects of environmental characteristics on slope stability in the highly fractured bedrock region of the Boston Mountains, northwest Arkansas. Field measurements, to determine characteristics and possible controls of 10 shallow slope failures along an interstate highway, revealed that slope failures occurred within a relatively narrow range of slope angles (17–36°) and in loamy soils. Based on field observations, flume experiments were conducted to investigate the relationships between soil texture, slope angle, bedrock fractures, soil compaction, and slope instability. Time to failure differed (p < 0.05) among treatment combinations. Generally, slopes composed of loam were more stable than slopes composed of sand. Time to failure decreased more on slopes of 15–20° than on slopes of 20–25°. Flume slopes with sod cover never failed. This study provided a methodology for using field analyses of slope failures to guide laboratory experiments and demonstrated that complex interactions among environmental factors work to stabilize or compromise steep (>20°) slopes.

A study of initial motion of soil aggregates in comparison with sand particles of various sizes

Critical shear stress and threshold stream power are two important soil characteristics controlling detachment of soil particles by runoff and have been used in process-based erosion models such as WEPP, GUEST and EUROSEM. In this research, laboratory experiments were conducted in a 20×350cm flume to study the effects of particle size and density on initial motion. Two contrasting soil samples, a well-aggregated forest soil and non-cohesive fluvial sand, were used to provide particles with different densities. Each sample was divided into six size classes. Flow bed in the flume was roughed according to testing area for each size class using a plate which sand particles from each size class were glued on it. The initial motion of the particles was determined by two methods. In the first method, slope was increased gradually for a given constant discharge until particles start to move from every point of the testing area. In the second method, flume slope was set to a given steepness and discharge was gradually increased until particles start to move. Three different discharges and three slopes were tested in the first and second methods, respectively. Each test replicated two times. Analysis of the data showed that the particle size and density and also their interaction significantly affect (P<0.001) critical shear stress and threshold stream power. The critical shear stress and threshold stream power increased with increasing particle size and density, but the impact of particle density is higher on the coarser particles than the finer ones. Threshold values measured for the sand particles were about 2.3 times of those measured for soil particles in the three coarser classes, this difference decreased to about 65% (1.65 times) in the three finer classes, and even the difference between the two types of particles was not significant for the finest class (0.125–0.053).

Development of a Method for Detecting Unstable Behaviors in Flume Tests using a Univariate Statistical Approach

We describe a method for detecting slope instability in flume tests using pore pressure and water content data in conjunction with a statistical control chart analysis. Specifically, we conducted univariate statistical analysis on x-MR control chart data (pore pressure and water content) collected at several points along the flume slope, which we separated into three parts: upper, middle, and lower. To assess our results in the context of landslide forecasting and warning systems, we applied control limit lines at <TEX>$1{\sigma}$</TEX>, <TEX>$2{\sigma}$</TEX>, and <TEX>$3{\sigma}$</TEX> levels of uncertainty. In doing so, we observed that dispersion time varies depending on the control limit line used. Moreover, the detection of instabilities is highly dependent on the position and type of sensor. Our findings indicate that different characteristics of the data on various factors predict slope failure differently and these characteristics can be identified by univariate statistical analysis. Therefore, we suggest that a univariate statistical approach is an effective method for the early detection of slope instability.