Debris Flow Discharge Research Articles

Study on debris flow discharge characteristics of check dam spillway

After a check dam is filled with sediment, the debris flow will flow out from the spillway. Insufficient discharge capacity of the spillway can lead to debris flow scouring the dam's shoulder and foundation. Therefore, it is necessary to study the discharge capacity of the spillway. It is of great importance for further optimizing the structural design of the check dam. This article analyzes discharge characteristics of debris flow of a spillway through a series of flume experiments. According to the motion states, it can be divided into five stages: contact stage of the spillway, flushing and climbing stage, increasing and reflux stage, stable discharge stage, and final discharge stage. We analyzed the influencing factors of the discharge capacity, including the type of spillway, bulk density of debris flow, scale of debris flow, flume gradient, and effective opening width of the spillway. Furthermore, we derived a calculation formula of discharge for the spillway based on Bernoulli's principle. Finally, we considered the influence of the ratio of flow area and Froude number to the discharge coefficient and established a calculation method of discharge. Consequently, we compared the calculated results with the measured results and found them to be in good agreement. Our research results provide a quantitative calculation method for the design of spillways and energy dissipation and erosion prevention projects under check dams, which is beneficial for improving engineering value and for better serving disaster prevention and reduction efforts.

Analyzing Debris Flow: Topographical Data and Discharge Rate Study

This study used an unmanned aerial vehicle (UAV) for aerial photogrammetry at the Seonseri debris flow site in Gokseong-gun, triggered by heavy rainfall in August 2020. Survey data facilitated the generation of orthographic images and high-resolution digital surface mode (DSM). Finite difference method (FDM) numerical analysis simulated debris flow, exploring the impact of discharge rate and topographic data among input variables. Applying the rational formula for determining debris flow discharge rate emphasized the significance of maximum rainfall intensity just before the event, with high estimated values for runoff coefficient and soil concentration. The study highlighted significant variations in debris flow simulation results based on topographical data accuracy, emphasizing the crucial role of precise site-specific topographical data.

A new method for detailed discharge and volume measurements of debris flows based on high-frequency 3D LiDAR point clouds; Illgraben, Switzerland

Debris flows are one of the most dangerous landslide types in mountainous regions. Their destructiveness is strongly controlled by their high peak discharge, which can be orders of magnitude larger than for floods. In order to reduce the associated hazards, detailed field measurements of natural debris flows are required to better constrain discharge and volume of these events. In this study, we used a high-frequency 3D LiDAR (light detection and ranging) scanner in combination with video cameras to measure key properties of a debris flow that occurred in the Illgraben catchment (Switzerland). Based on the LiDAR and video data, we directly measured i) front velocity ii) surge velocity iii) surface velocity and iv) cross-sectional area at sub-second intervals. We then estimated discharge and volume using these direct measurements and considering different channel bed geometry scenarios. We compared our results to estimates based on conventional methods and found that these more established methods substantially underestimate the (peak) discharge and volume for this event. Our results will be assessed in the future by analyzing more events, but our LiDAR-based method has the potential to provide much more detailed information on hazard-related debris-flow parameters, which will have important implications for understanding debris-flow processes and ultimately reducing their risk.

Debris flow characteristics of the compound channels with vegetated floodplains

Compound cross-sections with vegetated floodplains are a common type of cross-section in debris-flow gullies. Floodplain vegetation participates in large-scale debris flow events and regulates debris-flow discharge. Extensive research has been conducted on the water flow characteristics of compound rivers. However, few studies have investigated the debris flow characteristics of compound channels in mountainous areas, particularly those of debris flow and flash flood inundation areas with vegetation. This study discusses the section characteristics of debris flow gullies with vegetated floodplains, gully evolution processes, and their influence on debris flow. The results show that the compound debris flow gully with a vegetated floodplain is formed in the gully from the mature stage to the old-mature stage. The compound sections are developed in flow areas with a gentle slope, which can be bilateral floodplain, unilateral floodplain, and multi-main gully floodplain types. Owing to the vegetation of the floodplain, the roughness of the channel increases, which makes the beach roughness coefficient much larger than that for the main channel. In the integrated Manning coefficient method, the error in resolving the flow velocity and discharge is large and cannot reflect the difference in velocities of the floodplain and main channel, therefore the sectional splitting method is most applicable. Influencing debris flow movement, limiting channel migration, and retaining debris flow to the main channel were the main contributions of the riparian forest zone.

Study of debris flow peak discharge at Kamikamihorizawa Creek

Prediction of the peak discharge of debris flow is one of the most important factors in mitigating debris flow disasters. Currently, empirical methods based on the relationship between the peak discharge and total debris flow volume (magnitude) for many debris flow events are used to estimate peak discharge for planning or designing debris flow countermeasures in Japan. In order to estimate the peak discharge of debris flow with high accuracy, the debris flow monitoring sensors with load cell and pressure sensor (hereafter referred to as a DFLP system), was installed to evaluate various characteristics during floods involving debris flows at Kamikamihorizawa Creek. During the debris flow that occurred on August 29, 2019 at Kamikamihorizawa Creek, seven surges corresponding to debris flow events were monitored by the DFLP system for a 20-minute period. Based on the relationship between the peak discharge and magnitude, the observation data of Kamikamihorizawa Creek, Illgraben and Schipfenbach has been added to previous data from the literature and the relationship has been updated. The peak discharge and magnitude of debris flow on August 29, 2019 at Kamikamihorizawa Creek exhibited distributions similar to past observation data, which shows that the relationship between peak discharge and magnitude follows a similar trend.

Reconstruction of debris flow in the Gerkhozhan-Su river valley based on the chain modeling

The paper presents the reconstruction of the most catastrophic debris flows in the Gerkhozhan-Su river valley (North Caucasus, Russia) based on a chain of mathematical models. Transport-shift model was applied for 6 sections of debris flow formation or intense material increment, while for the rest the FLO-2D hydrodynamic model was used. A number of numerical experiments were carried out in the transport-shift model for a section of a debris flow origination site with a change in the parameters of a potential debris flow-forming soils, such as initial moisture content and density. According to the simulation results, with a rise in moisture content, the maximum debris flow discharge can increase by about 2.8 times. Modeling of debris flow in the Gerkhozhan-Su river valley was conducted for the case of low density debris flow. Based on the results, debris flow wave hydrographs were obtained at 12 sections. The results of modeling are in general agreement with the commonly accepted reconstructed pattern of the debris flow in 2000 and values obtained by videomaterials.

기후변화를 고려한 토석류 재해취약지역 레질리언스 강화를 위한 연구

Recently, climate change has caused serious natural disasters at the vulnerable areas with many mountainous regions. This study analyzes the behavior of debris flow with respect to time elapse by applying various precipitation, mountain slope change, and the categories of vegetation loosened in mountainous areas. The behavior of debris flow is debris flow discharge and water depth. In addition, the runout length of debris flow passed through the channel and reached the downstream according to the change of the water supply and slope was measured. The larger the supply flow, the higher the debris flow discharge, and the second peak value became faster as the supply flow increased, and the slope became steeper. In the category where the multiplier of vegetation for debris flow is large, the fluctuation period was made long, and the amplitude of the fluctuation was also made large. As for the debris flow runout length, the supply flow was large and it was spread in a considerable range on steep slopes. This study will provide various information such as establishing measures for debris flow occurring in vulnerable areas to natural disasters due to climate change, or establishing a plan for strengthening resilience.

Evaluation of kinematic parameters and characteristics of the source zone of the debris flow in Kongniba Watershed

The characteristics of the source zone of the debris flow watershed is one of the most significant factors governing debris flows initiation, at the same time it also plays a crucial role for disaster risk evaluation. With the aim of obtaining the basic characteristics of the source zone and computing the kinematic parameters, field investigations were conducted comprehensively, combining with the results of remote sensing interpretation, the origin and distribution regulations can be identified, and total amount of the loose solid materials can be determined, the corresponding value is 4.91×106 m3. Using the collected data of this watershed, and with the help of previous theoretical models, the kinematic parameters under different rainfall frequencies are calculated, which including debris flow discharge, total volume of one-time debris flow and the total volume of solid materials. Such parameters are helpful and essential for debris flow disasters evaluation, prevention and designing mitigation measures.

Catastrophe process of outburst debris flow triggered by the landslide dam failure

Strong earthquakes can induce large amounts of loose solid materials, forming landslide dams and blocking narrow flow channels. Under extreme rainfall conditions, instability can lead to an outburst of debris flow once the landslide dam has formed it. On July 10, 2013, a volume of 4.5 × 104 m3 of debris flow occurred in the Yangling gully, Wenchuan County, China. This event can be categorized as an outburst of the debris flow that might seriously threaten valley residents, existing sediment transport countermeasure works, and road infrastructures. This paper describes a typical outburst of debris flow, calculates its obstructive coefficient, simulates the process under various recurrence intervals, and analyzes the efficacy of a new mitigation project.Related research results have laid the foundation for further study of the risk assessment and early warning of debris flow due to landslide dam failure. In this paper, an accurate computational model for the obstructive coefficient, closely related to the flow amplification effect, is established based on a dam break's physical experiments. Combined with the numerical calculation method, the movement process of the Yangling gully was simulated under the old artificial dam and the flow channel engineering conditions. By comparing the measured and the simulated accumulation area, the verification results illustrate that the accumulation area considering the obstructive coefficient model is closer to the measured value. Based on the obstructive coefficient computational model, the results illustrate the outburst of debris flow discharge for various recurrence intervals (50, 100, and 200 years respectively) to perform scenario simulations of Yangling gully under the new mitigation project conditions.

RWM을 활용한 토석류 피해예측지도의 사방댐 효과 적용 가능성 검토

Debris flow transports lots of sediments downstream that cause damage to human lives and properties. The accurate estimation of the debris flow hazard zone is a critical factor of the successful early-warning and evacuation for reducing the debris flow risk. Korea Forest Service has developed a debris flow hazard map using Random Walk Model (RWM). Meanwhile, because check dams in forest watersheds capture discharged debris, the effect of check dams should be considered for mapping the debris flow hazard zone. This study analyzed the effect of check dams on debris flow discharge using RWM with the check dam module. As a result, RWM seems to simulate the sediment capture by check dams. However, the total deposit areas were not significantly different despite the effect of check dams because of input parameters and the flow direction calculation algorithm of RWM. Further studies on appropriate spatial resolution and initial sediment volume should be conducted to improve the debris flow hazard map.

New insights into the delayed initiation of a debris flow in southwest China

On 6 July 2020, 3 h 40 min after rainfall stopped, a delayed debris-flow disaster occurred due to colluvium deposits in a hollow region (CDH) in the Chenghuangmiao Gully, Sichuan Province, China, resulting in 4 deaths and 27 injuries. This study explores the initiation process of the delayed debris flow and the cause for the delay. Field investigations, catchment geometry interpretation, laboratory tests, theoretical calculations, and fluid–solid coupling numerical simulation were performed to obtain landslide parameters and understand the mechanisms of the event. Results show that (1) the event was a giant low-frequency viscous debris flow. (2) It was initiated by the delayed landslide process under the influence of back-end confluence. (3) The debris-flow discharge in the main gully increased over 19.5 min. (4) The seepage process inside the CDH continued for 3 h 20 min after the rainfall stopped before the pore pressure and reduction in strength were sufficient to initiate the debris flow. This research provides new insights on delayed debris-flow disasters and can be a reference for improving disaster management systems, especially monitoring and early warning systems, thereby avoiding future casualties.

Designing conduit sabo dam series as a debris flow protection structure

A high potential area for landslides was identified upstream of the Air Beras River on Bukit Beriti Besar which was feared to generate debris flow through the Air Beras River. One of the preventive efforts that can be conducted for debris flow is the sabo dam. This study aims to design a series of conduit sabo dams and evaluate the structure stability according to SNI 2851:2015 and Technical Standards and Guidelines for Planning and Design of Sabo Structures (JICA, 2010). By using the design discharge of debris flow of 120 m3/s, the velocity of 5.06 m/s, and the inclination of the riverbed of around 6.16°, the spillway height of the Sabo Dam 1 was determined to be 3 m, while the spillway height of Sabo Dam 1 was 2 m. The Sabo Dam 1 has a height of 10 m and a width of 30 m with a total manageable volume of 49,600 m3 while the Sabo Dam 2 has a height of 10 m and a width of 45 m with a total manageable volume of 91,500 m3. The safety factors of the sabo dam in the debris flow condition were 2.14 for overturning, 1.50 for sliding, and 5.74 for bearing capacity. Based on the result, the conduit sabo dam series effectively controls the destructive power of debris flow.

Estimation of runoff sediment volume and peak discharge of debris flow based on a stochastic method and effects of drainage basin area, precipitation and geology on them

Estimation of runoff sediment volume and peak discharge of debris flow based on a stochastic method and effects of drainage basin area, precipitation and geology on them

Combining Instrumental Monitoring and High-Resolution Topography for Estimating Sediment Yield in a Debris-Flow Catchment

ABSTRACT In mountain basins, long-term instrumental monitoring coupled with high-resolution topographic surveys can provide important information on sediment yield. The Gadria catchment, located in the eastern Italian Alps, typically features several low-magnitude flood episodes and a few debris-flow events per year, from late spring to late summer. Beginning in 2011, sensors devoted to debris-flow detection (geophones, video cameras, flow stage sensors) were installed along the main channel, upstream of a retention basin. In case of debris flows, high-resolution topographical surveys of the retention basin are carried out multiple times per year. Rainfall is measured in the lower part of the catchment and at the headwaters, while passive integrated transponder tracing of bedload was performed in the main channel during spring and summer 2014. In this work, we present the reconstruction of the sediment dynamics at the catchment scale from 2011 to 2017. Results show that (i) coarse sediment yield is dominated by the few debris flows occurring per year; (ii) debris-flow volume estimations may be significantly different—up to 30 percent lower—when performed through a digital elevation model of difference analysis, compared to the time-integration of the debris-flow discharge estimates; (iii) using this latter method, the volumes are affected by significant uncertainties, particularly for small values of flow depth; and (iv) rainfall analysis permits us to characterize debris-flow initiation but also highlights difficulties in discriminating triggering from non-triggering rainstorms if based on rainfall duration and intensity only.

Risk assessment of Sichuan–Tibet Highway susceptible to debris flows at Suotong Basin, southeastern Tibet

The planned Sichuan–Tibet Highway will pass through many debris flow-prone areas. Suotong catchment with a drainage area of 38.03 km2, a tributary of Parlung Zangbo River in the Bomi County of Tibet, has not experienced large-scale debris flows since 1991. Field survey and image interpretation show that glacial till in the catchment has volume of approximately 160 mm3 and is the primary source of loose materials for debris-flow reoccurrence. Once large glacial debris flows occur, they will cause harm to the highway. A comprehensive method including engineering geology, hydraulics, and computational mathematics is developed to quantitatively assess the debris-flow risk to the highway. The magnitude and peak discharge of glacial debris flows of a 100 year return period are calculated using empirical relationships in this region. The peak velocity at the outlet can reach 6.75 m/s, and the peak discharge is 6238 m3/s for such a return period. The Saint–Venant equations governing debris-flow movements are numerically solved by finite difference method. The simulated results are close to those by empirical methods. The hazard value at the alluvial fan is as high as 24.7 according to the numerical simulation. Two routing schemes (one goes through the tunnel and other pass the bridge) are compared with each other. Although the bridge scheme is cheaper than the tunnel scheme, the bridge’s section cannot fully discharge debris flows within the 100-year return period. Therefore, the tunnel scheme is safer and more strongly recommended than the bridge scheme.

Analysis of discharge and area of the debris flow based on geological structural and rainfall levels in the slopes of Mount Abang, Kintamani

Geological structural and rainfall intensity causes the parameters of soil shear strength to decline, especially in the surface layer of soil in volcanic rocks that have not experienced weathering. Study of geological structures and rainfall intensity against the hazard of a landslide was destroyed on the slopes of Mount Abang in the Abang Batudinding Village. Soil investigations using the Geoelectric method and sampling at 6 boreholes. Geological analysis on interpretation of slope outcrops, average rainfall analysis of the Thiessen Polygon method and analysis of design flood discharge using the NHSU method. Analysis results show the morphology of the slopes of Mount Abang with a slope of more than 40% and lithology of weathered volcanic rocks consisting of volcanic breccias, and tuffs breccias in conditions rather mild to moderate weathering, if have average effective rainfall for 10-50 years at 238 mm/day. The results also show that the peak discharge of debris flow was 98.639 m3/sec with the volume of debris flow 50072.85 m3 and the width of the range was 49.5 m. This debris flow volume indicated that residents around the river with a range of 49.5 m are at risk of debris flow sediment with a thickness of 1-1.5 m.

Laboratory study on the characteristics of large wood and debris flow processes at slit-check dams

Large wood (LW) in debris flows during flooding can cause significant damage to check dams, bridges, and other major infrastructure in its flow path. When LW accumulates and forms logjams, large volumes of sediment can be deposited, resulting in increased backwater. The logjams can then suddenly collapse, with the deposited sediment and accumulated water increasing the magnitude of debris-flow peak discharge. To better understand the characteristics of debris flow discharge caused by LW accumulation and collapsed logjams, as well as the associated magnitude amplification effects, a series of experiments was carried out in a laboratory experimental channel. The main purpose of this study was to analyze the process of LW accumulation and collapse and to determine the magnitude amplification ratio of the debris flow peak discharge with LW. The results revealed three types of debris flow movement with LW: flow with no clogging or breakage, flow with clogging but without breakage, and flow with both clogging and breakage. The results indicated a significant effect on the magnitude amplification ratio caused by LW clogging and breakage. The maximum magnitude amplification ratio was 1.60 in the experiments, with a relative LW length and volume of 0.875 and 0.75, respectively, during the clogging and breakage process.

Debris Flow Generation Based on Critical Discharge: A Case Study of Xiongmao Catchment, Southwestern China

Generation of debris flows is related to poorly sorted mixtures of soil, catchment topography, and rainfall characteristics. Runoff in a valley resulting from intensive rainfall can induce sediment movement within stream beds or along adjacent banks. The water flow in channels is affected by rainfall parameters such as duration, intensity, cumulative rainfall, etc., and is the key factor in debris movement. In this paper, the rainfall characteristics and occurrence conditions of debris flow in Xiongmao Gully on 26 July 2016 were explored. Using data from field surveys and indoor simulation experiments, evaluations of critical discharge parameters for debris movement were performed. Furthermore, debris distribution and the critical discharge characteristics were analyzed via investigation of the catchment topography and cause of the debris flow, and analysis was made of the critical discharge parameters initiating channel debris movement. A K-value clustering analysis method was applied to characterize the rainfall pattern of the study area and its effects on calculation of debris flow. The results showed that for the debris flow in Xiongmao Gully, the debris initiation in the middle reaches of the gully provided the majority of solid particles for the disaster on 26 July 2016, and the upstream confluent provided catchment. Based on the relationship determined by laboratory tests, the calculated critical discharge was 43.8 m3/s, less than the peak discharge (Qc = 66.7 m3/s) calculated by morphological method. In addition, it was indicated that the dominant rainfall patterns of the studied area were first-quartile and second-quartile, i.e., the rainfall occurred primarily at the early or middle stage of this rainfall event. The critical discharge for the debris flow on 26 July was achieved at 5% rainfall frequency, and the larger runoff volume was generated from a short heavy rainfall. According to specific catchment characteristics, such as distributed hydrological analysis, critical discharge, and rainfall pattern of debris flow, forewarning of a damaging debris flow could be made more effective.

Glacial Lake Inventory and Lake Outburst Flood/Debris Flow Hazard Assessment after the Gorkha Earthquake in the Bhote Koshi Basin

Glacial lake outburst floods (GLOF) evolve into debris flows by erosion and sediment entrainment while propagating down a valley, which highly increases peak discharge and volume and causes destructive damage downstream. This study focuses on GLOF hazard assessment in the Bhote Koshi Basin (BKB), where was highly developed glacial lakes and was intensely affected by the Gorkha earthquake. A new 2016 glacial lake inventory was established, and six unreported GLOF events were identified with geomorphic outburst evidence from GaoFen-1 satellite images and Google Earth. A new method was proposed to assess GLOF hazard, in which large numbers of landslides triggered by earthquake were considered to enter into outburst floods enlarge the discharge and volume of debris flow in the downstream. Four GLOF hazard classes were derived according to glacial lake outburst potential and a flow magnitude assessment matrix, in which 11 glacial lakes were identified to have very high hazard and 24 to have high hazard. The GLOF hazard in BKB increased after the earthquake due to landslide deposits, which increased by 216.03 × 106 m3, and provides abundant deposits for outburst floods to evolve into debris flows. We suggest that in regional GLOF hazard assessment, small glacial lakes should not be overlooked for landslide deposit entrainment along a flood route that would increase the peak discharge, especially in earthquake-affected areas where large numbers of landslides were triggered.

Experimental investigation of blocking and discharge regulation function of window-frame dam in viscous debris flow control

The blocking of a window-frame dam and the discharge regulation are both important basic control features for characterizing the regulatory effect of a window-frame dam on debris flow. To better understand the regulatory effect of a window-frame dam on debris flow, physical model tests were carried out to investigate the flow pattern, trapping, and regulating characteristics when debris flow passed through a window-frame dam. The results revealed that the opening size of the dam and bulk density of the debris flow were the main factors affecting the blocking degree of the dam, followed by flume gradient. And a new comprehensive criterion for the blocking degree is proposed considering the multiple factors. Window-frame dams can regulate the discharge of debris flow to a certain extent under different conditions, and the control effect of discharge of viscous debris flow is not only reflected on the reduction of peak discharge, but also on the delayed effect of viscous debris flow. Moreover, the reduction rate of the peak discharge of debris flow is related to the blocking degree of the dam, which implies that designers should consider more factors in the determining the opening parameters of window-frame dams.