scholarly journals The Model for Dilution Process of Landslide Triggered Debris Flow —A Case of Guanba River in Tibet Southeastern Plateau

2018 ◽  
Vol 22 (2) ◽  
pp. 103-111 ◽  
Author(s):  
Jun Li ◽  
Ningsheng Chen
Keyword(s):  
Debris Flow ◽  
Water Flow ◽  
Debris Flows ◽  
Evaluation Model ◽  
Flow Density ◽  
Flow Section ◽  
Average Depth ◽  
Flow Discharge ◽  
Study Results ◽  
Density Evaluation

Understanding and modeling the downstream dilution process of a landslide triggered debris flow is the foundation for recognizing the boundary condition and dilution mechanism of this type of debris flow, and this serves as the theoretical basis for the categorized control of viscous debris flows, diluted debris flows, hyperconcentration flows and flash floods in a drainage basin. In this study, taking as an example a typical debris flow that occurred in the Guanba River on Tibet’s southeastern plateau on July 6th, 1998, empirical models are used to calculate the density, water flow discharge, debris flow discharge, average depth of loose materials and channel gradient at 11 cross-sections upstream to downstream in the debris flow. On this basis, the dilution characteristics and debris flow dilution process are analyzed in this study. According to the correlation between the debris flow density and the water-soil ratio and channel gradient, we have established the density evaluation model for the debris flow dilution process, which can predict the dilution process of a landslide triggered debris flow. The study results include the following four aspects: (1) The key factors in the dilution process of landslide triggered debris flows are the water flow discharge, average depth of loose materials and channel gradient. (2) The debris flow dilution characteristics in the Guanba River in 1998 include the occurrence of the debris flow dilution process after a significant increase in the water-soil ratio; an increase in the proportion of fine particles after dilution of the debris flow; and the size distribution of grain is “narrowed.” (3) In accordance with the density and dilution characteristics, the debris flow dilution process in the Guanba River can be divided into the upstream viscous debris flow section, midstream and downstream transitional debris flow section and downstream diluted debris flow section. (4) The density evaluation model for the debris flow dilution process is expressed by the Lorentz equation, and this model can reflect the debris flow dilution process such that the debris flow density will decrease gradually with an increase in the water-soil ratio and decrease in channel gradient. The density evaluation model for the debris flow dilution process has been verified by three debris flow cases, which include Gaoqiao Gully, Haizi Valley, and Aizi Valley

scholarly journals Discharge of landslide-induced debris flows: case studies of Typhoon Morakot in southern Taiwan

2014 ◽  
Vol 2 (1) ◽  
pp. 315-346
Author(s):  
J.-C. Chen ◽  
M.-R. Chuang
Keyword(s):  
Debris Flow ◽  
Case Studies ◽  
Debris Flows ◽  
Maximum Flow ◽  
Field Investigation ◽  
Typhoon Morakot ◽  
Flow Discharge ◽  
Modeling Software ◽  
Southern Taiwan ◽  
Deposition Depth

Abstract. Three debris-flow gullies, the Hong-Shui-Xian, Sha-Xin-Kai, and the Xin-Kai-Dafo gullies, located in the Shinfa area of southern Taiwan were selected as case studies of the discharge of landslide-induced debris flows caused by Typhoon Morakot in 2009. The inundation characteristics of the three debris flows, such as the debris-flow volume, the deposition area, maximum flow depth, and deposition depth, were collected by field investigations and simulated using the numerical modeling software FLO-2D. The discharge coefficient cb, defined as the ratio of the debris-flow discharge Qdp to the water-flow discharge Qwp, was proposed to determine Qdp, and Qwp was estimated by a rational equation. Then, cb was calibrated by a comparison between the field investigation and the numerical simulation of the inundation characteristics of debris flows. Our results showed that the values of cb range from 6 to 18, and their values are affected by the landslide ratio The empirical relationships between Qdp and Qwp were also presented.

scholarly journals Quantitative Analysis of the Debris Flow Societal Risk to People Inside Buildings at Different Times: A Case Study of Luomo Village, Sichuan, Southwest China

2021 ◽  
Vol 8 ◽  
Author(s):  
Li Wei ◽  
Kaiheng Hu ◽  
Jin Liu
Keyword(s):  
Quantitative Analysis ◽  
Debris Flow ◽  
Debris Flows ◽  
Evaluation Model ◽  
Alluvial Fan ◽  
Economic Losses ◽  
Rural Settlements ◽  
Societal Risk ◽  
Flow Intensity ◽  
The Village

Debris flows, which cause massive economic losses and tragic losses of life every year, represent serious threats to settlements in mountainous areas. Most deaths caused by debris flows in China occur in buildings, and the death toll is strongly dependent on the time people spend indoors. However, the role of time spent indoors in the quantitative analysis of debris flow risk has been studied only scarcely. We chose Luomo village in Sichuan atop a debris flow alluvial fan to study the influence of the temporal variation in the presence of people inside buildings on the societal risk. Two types of days (holidays vs. workdays) and two diurnal periods (daytime vs. nighttime) were considered in our risk evaluation model. A questionnaire survey was conducted for each family in the village, and the probability of the temporal impact of a debris flow on every household was calculated based on the average amount of time each member spent in the house. The debris flow hazard was simulated with FLO-2D to obtain the debris flow intensity and run-out map with return periods of 2, 10, 50, and 100 years. The risk to buildings and societal risk to residents were calculated quantitatively based on the probabilities of debris flow occurrence, the probability of the spatial impact, and the vulnerabilities of buildings and people. The results indicated that societal risk on holidays is always higher than that on weekdays, and societal risk at night is also much higher than that in the daytime, suggesting that the risk to life on holidays and at night is an important consideration. The proposed method permits us to obtain estimates of the probable economic losses and societal risk to people by debris flows in rural settlements and provides a basis for decision-making in the planning of mitigation countermeasures.

Debris flow monitoring in China

2020 ◽  
Author(s):  
Xiaojun Guo
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Flow Characteristics ◽  
Western China ◽  
Flow Density ◽  
Flow Depth ◽  
Jinsha River ◽  
Flow Monitoring ◽  
Jiangjia Gully ◽  
Set Up

<p><strong>Abstract: </strong>Debris flow monitoring provides valuable data for scitienfic research and early warning, however, it is of difficulty to sucessfully achive because of the great damage of debris flows and the high cost. This report introduces monitoring systems in two debris flow watersheds in western China, the Jiangjia gully (JJG) in Yunnan Province and the Ergou valley in Sichuan Province. JJG is loacted in the dry-hot valley of Jinsha River, and the derbis flows are frequent due to the semi-arid climate, deep-cut topography and highly weathered slope surface. A long-term mornitoring work has been conducted in JJG and more than 500 debris flows events has been recorded since 1965. The monitoring system consists of 10 rainfall gauges and a measuring section, with instruments to measure the flow depth and velocity; and flow density is measured through sampling the fresh debris flow body. Ergou lies in the Wenchuan earthquake affected area and the monitoring began in 2013 to investigate the characteristics and development tendency of post-earthquake debris flows. Three stations were set up in the mainstream and tributaries, with instruments to measure the flow depth, velocity, and density. Over 10 debris flow events were recorded up to date.</p><p>Based on the monitoring output, the rainfall spatial distribution and thresholds for debris flows are proposed. The debris flow dynamics characteristics are analyzed, and the relations between the parameters, e.g. density, velocity, discharge and grain compositions are presented. The debris flow formation modes and the mechanisms in different regions are discriminated and simulation methods are suggested. It is anticipated that the monitoring results will promote understanding of debris flow characteristics in the western China.</p><p><strong>Keywords:</strong> Debris flow, monitoring, rainfall, discharge, formation. </p>

Recognition and Occurrence of Different Sediment-Water Flows Triggered by High-Magnitude Hydrological Events in Mountain Catchments

2020 ◽  
Author(s):  
Andrea Brenna ◽  
Nicola Surian ◽  
Marco Borga ◽  
Massimiliano Ghinassi ◽  
Lorenzo Marchi
Keyword(s):  
Debris Flow ◽  
Water Flow ◽  
Debris Flows ◽  
Field Survey ◽  
Medium Size ◽  
Transport Mechanisms ◽  
High Magnitude ◽  
Hyperconcentrated Flow ◽  
Channel Slope ◽  
Sediment Mobilization

<p>Sediment mobilization in small-medium size mountain catchments occurs by different flow types, categorized as debris-flows, hyperconcentrated-flows and water-flows, depending on the physical mechanisms governing flow rheology and particles interaction. During high-magnitude flow events, such transport mechanisms may take place concurrently in the same catchment at different sites of the channel network. One of the most important tasks in investigating dynamics of floods in these mountain catchments is to identify the transport mechanisms, since different flow types induce peculiar geomorphological hazards and dynamics. This work aims to improve criteria to recognize different flow types, with particular regard to hyperconcentrated-flows, and to analyze the transport mechanisms in mountain catchments in response to high-magnitude hydrological events.</p><p>Since direct monitoring of sediment mobilization during a flood is extremely difficult, a sound alternative is to consider the characteristics of the deposited material, which depend on the rheological proprieties of related flow. Through an extensive literature review, we identified the diagnostic criteria of the different flow types, grouping them in morphological and sedimentological evidences. A field-survey worksheet has been developed to ease the field-data collection and interpretation. The case-study selected for applying the survey procedure is the Tegnas catchment (Dolomites, Italy), a mountain basin draining an area of 51 km<sup>2</sup> affected by the Vaia Storm in October 2018, which induced large floods in several catchments of the Eastern Italian Alps. The deposits field-survey has been conducted in 35 sub-reaches of the Tegnas river and its major tributaries. In addition, we carried out detailed grain-size analyses, measured the angle of clasts-imbrication and collected samples for estimating the vegetal organic matter content through Loss-of-ignition procedure.</p><p>Field criteria allowed us to classify each sub-reach according to the deposits left after the event. Most of the steep tributaries have been interested by debris-flows, but also hyperconcentrated-flows have been recognized. Along the main stem, water-flow was the dominant process, although debris-flows and hyperconcentrated-flows deposits are documented where channel slope was very high (i.e. from 9 to 21%).   Hyperconcentrated-flow deposits occur also in the lower sub-reaches (i.e. channel slope from 0.3 to 6%), either at the confluence with debris-flow fed tributaries of where severe bank erosion occurred. We statistically analyzed data about clast imbrication angle (δ) and content of vegetal organic matter (OM<sub>LOI</sub>) obtaining significant results for both parameters. δ measured in debris-flow (50°-65°) and hyperconcentrated-flow deposits (45°-60°) is considerably higher than in water-flow sediments (30°-40°). Debris-flow and hyperconcentrated-flow deposits have higher OM<sub>LOI</sub> (2.5-5.5%) than water-flow deposits (1.5-3%). </p><p>The combination of field diagnostic-criteria and quantitative measure of additional parameters allows a reliable recognition of the flow types based on post-flood survey. Besides, this study allowed to point out that during high-magnitude floods the sediment mobilization in small-medium size catchments occurs through mechanisms that can be different from those expected for ordinary hydrological events using morphometric approaches. Solid material concentration or dilution (e.g. due to lacking of sediment sources or sediment disconnectivity) can explain the “unexpected” flow types during high magnitude events.</p>

scholarly journals EDDA: integrated simulation of debris flow erosion, deposition and property changes

2014 ◽  
Vol 7 (6) ◽  
pp. 7267-7316
Author(s):  
H. X. Chen ◽  
L. M. Zhang
Keyword(s):  
Debris Flow ◽  
Yield Stress ◽  
Water Flow ◽  
Large Scale ◽  
Limit Equilibrium ◽  
Flow Density ◽  
Catchment Scale ◽  
Flow Process ◽  
One Dimensional ◽  
Property Changes

Abstract. Debris flow material properties change during the initiation, transportation and deposition processes, which influences the runout characteristics of the debris flow. A quasi-three-dimensional depth-integrated numerical model, EDDA, is presented in this paper to simulate debris flow erosion, deposition and induced material property changes. The model considers changes in debris flow density, yield stress and dynamic viscosity during the flow process. The yield stress of debris flow mixture is determined at limit equilibrium using the Mohr–Coulomb equation, which is applicable to clear water flow, hyper-concentrated flow and fully developed debris flow. To assure numerical stability and computational efficiency at the same time, a variable time stepping algorithm is developed to solve the governing differential equations. Four numerical tests are conducted to validate the model. The first two tests involve a one-dimensional dam-break water flow and a one-dimensional debris flow with constant properties. The last two tests involve erosion and deposition, and the movement of multi-directional debris flows. The changes in debris flow mass and properties due to either erosion or deposition are shown to affect the runout characteristics significantly. The model is also applied to simulate a large-scale debris flow in Xiaojiagou Ravine to test the performance of the model in catchment-scale simulations. The results suggest that the model estimates well the volume, inundated area, and runout distance of the debris flow. The model is intended for use as a module in a real-time debris flow warning system.

scholarly journals EDDA 1.0: integrated simulation of debris flow erosion, deposition and property changes

2015 ◽  
Vol 8 (3) ◽  
pp. 829-844 ◽  
Author(s):  
H. X. Chen ◽  
L. M. Zhang
Keyword(s):  
Debris Flow ◽  
Yield Stress ◽  
Water Flow ◽  
Large Scale ◽  
Limit Equilibrium ◽  
Flow Density ◽  
Catchment Scale ◽  
Flow Process ◽  
Runout Distance ◽  
Property Changes

Abstract. Debris flow material properties change during the initiation, transportation and deposition processes, which influences the runout characteristics of the debris flow. A quasi-three-dimensional depth-integrated numerical model, EDDA (Erosion–Deposition Debris flow Analysis), is presented in this paper to simulate debris flow erosion, deposition and induced material property changes. The model considers changes in debris flow density, yield stress and dynamic viscosity during the flow process. The yield stress of the debris flow mixture determined at limit equilibrium using the Mohr–Coulomb equation is applicable to clear water flow, hyper-concentrated flow and fully developed debris flow. To assure numerical stability and computational efficiency at the same time, an adaptive time stepping algorithm is developed to solve the governing differential equations. Four numerical tests are conducted to validate the model. The first two tests involve a one-dimensional debris flow with constant properties and a two-dimensional dam-break water flow. The last two tests involve erosion and deposition, and the movement of multi-directional debris flows. The changes in debris flow mass and properties due to either erosion or deposition are shown to affect the runout characteristics significantly. The model is also applied to simulate a large-scale debris flow in Xiaojiagou Ravine to test the performance of the model in catchment-scale simulations. The results suggest that the model estimates well the volume, inundated area, and runout distance of the debris flow. The model is intended for use as a module in a real-time debris flow warning system.

scholarly journals Discharge of landslide-induced debris flows: case studies of Typhoon Morakot in southern Taiwan

2014 ◽  
Vol 14 (7) ◽  
pp. 1719-1730 ◽  
Author(s):  
J.-C. Chen ◽  
M.-R. Chuang
Keyword(s):  
Debris Flow ◽  
Case Studies ◽  
Debris Flows ◽  
Maximum Flow ◽  
Field Investigation ◽  
Typhoon Morakot ◽  
Flow Discharge ◽  
Field Investigations ◽  
Modeling Software ◽  
Southern Taiwan

Abstract. Three debris-flow gullies, the Hong-Shui-Xian (HSX), Sha-Xin-Kai (SXK), and Xin-Kai-Dafo (XKD) gullies, located in the Shinfa area of southern Taiwan, were selected as case studies on the discharge of landslide-induced debris flows caused by Typhoon Morakot in 2009. The inundation characteristics of the three debris flows, such as the debris-flow volume V, deposition area Ad, and maximum flow depth, were collected by field investigations and simulated using the numerical modeling software FLO-2D. The discharge coefficient cb, defined as the ratio of the debris-flow discharge Qdp to the water-flow discharge Qwp, was proposed to determine Qdp, and Qwp was estimated by a rational equation. Then, cb was calibrated by a comparison between the field investigation and the numerical simulation of the inundation characteristics of debris flows. Our results showed that the values of cb range from 6 to 18, and their values are affected by the landslide ratio RL. Empirical relationships for cb versus RL, Qdp versus Qwp, Qdp versus V, and Ad versus V are also presented.

Sediment-water flows in mountain catchments: Variability in response to high-magnitude hydrological events

2021 ◽  
Author(s):  
Andrea Brenna ◽  
Marco Borga ◽  
Massimiliano Ghinassi ◽  
Lorenzo Marchi ◽  
Mattia Zaramella ◽  
...  
Keyword(s):  
Debris Flow ◽  
Water Flow ◽  
Debris Flows ◽  
Transport Mechanisms ◽  
Stream Network ◽  
Water Flows ◽  
High Magnitude ◽  
Sediment Transfer ◽  
Flood Deposits ◽  
Debris Floods

<p>Sediment transfer in mountain streams occurs by processes classified as debris flows, hyperconcentrated flows, debris floods, and water flows. One of the most important tasks in investigating floods in mountain catchments is to identify the transport mechanisms since different sediment-water flows induce peculiar geomorphological dynamics and hazards. This study aims at testing how the energy of water and the amount of sediment involved during a high-magnitude hydrological event can modify the mechanisms of sediment transfer with respect to those occurring during ordinary floods.</p><p>The selected case study is the Tegnas catchment (Dolomites, Italy), which, in October 2018, was affected by a severe hydrological event (Vaia Storm) with a recurrence interval of about 200 years. The studied catchment drains an area of 51 km<sup>2</sup>, with a range in elevation between 2872 and 620 m a.s.l.. The classification of flows that occurred during the Vaia storm was addressed at the sub-reach scale applying a field survey protocol developed to classify the flood deposits based on their sedimentological and morphological features. Following the same approach, we also determined the flow types typifying the stream network during ordinary floods. Additionally, we considered flows predicted by three morphometric approaches for high-magnitude events, and took into account the geomorphological dynamics (e.g., channel changes) and the hydraulic constraints (i.e., unit stream power) that occurred during the Vaia storm.</p><p>Water flow was the dominant process during Vaia storm in the Tegnas main steam (12 sub-reaches), although debris flow and debris flood deposits were documented at 3 and 7 sub-reaches, respectively. Water flow was observed in response to ordinary events along the entire Tegnas Torrent. Most of the steep tributaries were affected by debris flows (6 tributaries), but also debris floods were recognized at 3 steep channels. The morphometric approaches had a satisfactory performance in predicting the two end-member flows, but often failed in recognizing sub-reaches affected by debris floods.</p><p>The comparison between the occurred high-magnitude flows, and the ordinary flows allowed us to infer the existence of relationships between the transport mechanisms, the hydraulic forcing, and channel dynamics. The upheaval of the ordinary flow types did not occur along the entire stream network. The transition from water flows to debris floods occurred for unit stream powers exceeding the threshold of 5000-6000 Wm<sup>-2</sup> or downstream of a channel delivering a large amount of sediment mobilized by debris flow to the receiving stream. The occurrence of debris floods, causing higher channel widening than water flows, appears to be facilitated by the injection of fine material into the flow, which can occur as consequence of channel-bank erosion and overbank floodwater re-entering the channel. Finally, morphometric approaches turned out to be adequate to provide a first-order discrimination of expectable high-magnitude flow types. However, the complex relationships found between flow types and a range of hydraulic, morphological, and geological controlling factors, reveal that a more detailed characterization is necessary for understanding the transport mechanisms and predicting geomorphic hazard that can affect specific channel sites during high-magnitude to extreme hydrological events.</p>

Investigating infrasound sources within Illgraben debris-flows

2021 ◽  
Author(s):  
Giacomo Belli ◽  
Emanuele Marchetti ◽  
Fabian Walter ◽  
Brian McArdell ◽  
Małgorzata Chmiel ◽  
...  
Keyword(s):  
Debris Flow ◽  
Early Warning ◽  
Debris Flows ◽  
Fluid Dynamic ◽  
Flow Characteristics ◽  
Maximum Flow ◽  
Dynamic Processes ◽  
Flow Density ◽  
Small Aperture ◽  
Flow Monitoring

<p>Debris flows are episodic gravitational currents, consisting of mixtures of water and debris in varying proportions. They occur in steep mountain torrents with volumes commonly exceeding thousands of m<sup>3</sup>. Given their unpredictability and their capability to transport large boulders, debris flows rank among the most dangerous natural hazards in mountain environments. Nevertheless, moderate flow velocities (typically < 10 m/s) make early warning in principle possible if the flows are detected early upon formation.</p><p>Infrasound studies of debris flows increased significantly in the last decade, focusing mostly on event detectability and application for early-warning. The use of infrasound arrays and the combined use of collocated seismic and infrasound sensors have turned out to be efficient systems for reliable detection of debris flows in near-real time.</p><p>Despite these advances, open questions remain about the possibility to infer debris-flow source characteristics and event magnitude from recorded infrasonic signals. This requires theoretical and/or empirical source models describing elastic energy radiation in the atmosphere, in the form of infrasound, and relating it with fluid dynamic processes within a debris flow. Infrasound radiated by debris-flows is believed to be generated by standing waves that develop at the free surface of the flow, but details of the involved dynamic processes are not fully understood.</p><p>Here, we present the analysis of infrasonic signals recorded with a small aperture array during the 2017-2020 debris-flow seasons in the Illgraben catchment (Switzerland, Canton Valais), including more than 20 events of variable sizes. In order to better understand infrasound source mechanisms and to investigate the fluid dynamics processes involved in the infrasonic energy generation, debris-flow infrasound signals are quantitatively compared with independent hydraulic information of the flow (velocity, maximum flow depth and flow density). Finally, we discuss the use of extrapolated empirical relationships between infrasound signal features and flow characteristics for debris-flow monitoring and risk management.</p><p> </p>

Investigation of the influence of the flow structure on the accuracy of flow measurement before a hydrometric structure in an open channel

2020 ◽  
pp. 41-44
Author(s):  
Anatoly Kusher
Keyword(s):  
Velocity Profile ◽  
Flow Velocity ◽  
Water Flow ◽  
Flow Measurement ◽  
Water Discharge ◽  
Critical Depth ◽  
Flow Measurements ◽  
Study Results ◽  
Flow Velocity Profile ◽  
Upstream Flow

The reliability of water flow measurement in irrigational canals depends on the measurement method and design features of the flow-measuring structure and the upstream flow velocity profile. The flow velocity profile is a function of the channel geometry and wall roughness. The article presents the study results of the influence of the upstream flow velocity profile on the discharge measurement accuracy. For this, the physical and numerical modeling of two structures was carried out: a critical depth flume and a hydrometric overfall in a rectangular channel. According to the data of numerical simulation of the critical depth flume with a uniform and parabolic (1/7) velocity profile in the upstream channel, the values of water discharge differ very little from the experimental values in the laboratory model with a similar geometry (δ < 2 %). In contrast to the critical depth flume, a change in the velocity profile only due to an increase in the height of the bottom roughness by 3 mm causes a decrease of the overfall discharge coefficient by 4…5 %. According to the results of the numerical and physical modeling, it was found that an increase of backwater by hydrometric structure reduces the influence of the upstream flow velocity profile and increases the reliability of water flow measurements.

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