FIELD INVESTIGATION INTO DEBRIS FLOW MECHANISM

1.INTRODUCTIONDebrisflowisadistincttypeofmassmovementcommonlytriggeredbyintenserainfallandmeltingsnowonsteephillslopes.Althoughgreateffortshavebeenmadeinthestudyofthemechanismofthemotion,considerableambiguitypersistsconcerningtheinitiationandmotionofdebrisflow.Debrisflowcanbeinitiatedinsteepslopebecauseofthehighgravitationalforceandcanalsobetriggeredbyheavyrainstormongentleslopebyhighscouringcapacityofthetorrentialflood.Debrisflowisturbulentbecauseofitshighflowvelocityinsomecircumstancesa…     

Soil and bedrock distribution estimated from gully form and frequency: A GIS-based decision-tree model for Lebanon

Torrential rainfall and relatively sparse vegetation in the Mediterranean region result in the development of gully systems and land degradation, notably on lands with specific types of soil and bedrock. This paper proposes a decision-tree model to predict the distribution of soil and bedrock susceptible to gully erosion (white Rendzinas and marly rocks) from the form and frequency of gullies. The study area is located in Lebanon and the model is linked to GIS. V-fold cross-validation of the pruned model indicates that gully features including cross-section size and shape, network frequency, types of meandering, and catchment area can explain 80% of variance in soil/rock properties. The overall accuracy of the soil/rock map was estimated to be ca. 87%. The proposed model is relatively simple, and may also be applied to other areas. It is particularly useful when information about soil and rock obtained from conventional field surveys is limited.     

滇西干沟金多金属矿深部及外围找矿预测

干沟金多金属矿是滇西地区开采近30年的小型金矿山,但近年来新增地质储量不断上升,受到地质学家的广泛关注。通过对干沟金多金属矿矿床成矿地质背景、矿区地质特征、矿体地质特征的综合研究分析,分别从成矿作用分析、矿化顺序、矿化结果总结了金多金属矿的成矿规律,并有针对性地进行了深部及外围预测,进一步指出了深部和外围找矿方向。     

Erosion processes and rates for gullies in granitic soils bathurst,new south wales,australia

Soil movement rates from fluted gully sides in New South Wales were measured over three years by erosion pins and survey. Erosion rates varied considerably over short distances from 0 to 53 mm yr^?1 with an average removal rate of 19-8 mm yr^?1.     

Two-dimensional numerical model for debris flows in the Jiangjia Gully, Yunnan Province

Debris flows are recurrent natural hazards in many mountainous regions.This paper presents a numerical study on the propagation of debris flows in natural erodible open channels,in which the bed erosion and sedimentation processes are important.Based on the Bingham fluid theory,a mathematical model of the two-dimensional non-constant debris flow is developed.The governing equations include the continuity and momentum conservation equations of debris flow,the sediment convection-diffusion equation,the bed erosion-deposition equation and the bed-sediment size gradation adjustment equation.The yield stress and shear stress components are included to describe the dynamic rheological properties.The upwind control-volume Finite Volume Method (FVM) is applied to discretize the convection terms.The improved SIMPLE algorithm with velocity-free-surface coupled correction is developed to solve the equations on non-orthogonal,quadrilateral grids.The model is applied to simulate a debris flow event in Jiangjia Gully,Yunnan Province and to predict the flow pattern and bed erosion-deposition processes.The results show the effectiveness of the proposed numercial model in debris flow simulation and potential hazard analysis.     

四川冕宁盐井沟泥石流综合治理工程浅议

1970年后盐井沟矿山泥石流频发。1986年以来建成的治理工程有:排土场导流堤,5号格(?)坝,3号拦沙坝,并正在开展着生物治理工程。综合治理工程发挥了良好的防护作用。     

CONTROL OF GULLY EROSION USING STIFF GRASSES

Concentrated flow can cause gully formation on sloping lands and in riparian zones. Current practice for riparian gully erosion control involves blocking the gully with a structure comprised of an earthen embankment and a metal or plastic pipe. Measures involving native vegetation would be more attractive for habitat recovery and economic reasons. To test the hypothesis that switchgrass （Panicum virgatum L.） hedges planted at 0.5-m vertical intervals within a gully would control erosion, a series of hedges was established in four concentrated flow channels. Two of the channels were previously eroded trapezoidal channels cut into compacted fill in an outdoor laboratory. The other two channels were natural gullies located at the edge of floodplain fields adjacent to an incised stream. While vegetation was dormant, artificial runoff events were created in the two laboratory gullies and one of the natural gullies using synthetic trapezoidal-shaped hydrographs with peak discharge rates of approximately 0.03, 0.07, and 0.16 m3/s. During these tests flow depth, velocity, turbidity, and soil pore water pressures were monitored. The fourth gully was subjected to a series of natural runoff events over a five-month period with peaks up to 0.09 m3/s. Flow depths in all tests were generally 〈 0.3 m, and flow velocities varied spatially and exceeded 2.0 m/s at the steepest points of the gullies. Erosion rates were negligible for controlled flow experiments, but natural flows in the fourth gully resulted in 1 m ofthalweg degradation, destroying the central portions of the grass hedges, most likely due to the highly erodible nature of the soils at this site. Geotechnical modeling of soil steps reinforced with switchgrass roots showed factors of safety 〉 1 for step heights 〈 0.5 m, but instability was indicated for step heights 〉1 m, consistent with the experimental observations.     

山区公路地质灾害减灾决策支持系统——以西藏古乡沟泥石流为例

由于复杂地形条件和地质条件以及降雨、地下水等因素的影响,山区公路易受到泥石流、滑坡、崩塌、溜砂坡等地质灾害的危害。文章在对山区公路地质灾害模型研究和分析的基础上,建立了滑坡稳定性分析、泥石流活动性分析、泥石流危险范围预测与危险性分区、滑坡区公路整治方案优选、拦砂坝优化设计等灾害分析模型和减灾决策模型,通过数据库、分析模型和决策模型的集成,建立了基于组件式GIS的山区公路地质灾害减灾决策支持系统。作为系统应用的实例,文章最后讨论了系统在古乡沟泥石流危险范围预测的应用,预测了一定条件下泥石流堆积扇上的泥深,泥石流运动过程中出现的最大泥深、最大速率、最大动量和最大动能,为古乡沟泥石流的预防和治理提供了科学依据。     

Rates and mechanisms of discontinuous gully erosion in a red-brown earth catchment,new south wales,australia

Rainfall, runoff, sediment discharge, and gully expansion were measured for five years in a small (45 ha) catchment in central N.S.W. Sixty per cent of the sediment produced from this catchment originated from gully erosion. Gully head erosion was episodic depending on pipe development, cracking, and soil detachment during small runoff events which prepared the heads for rapid soil movement by the infrequent large event.     

Integrated erosion control measures and environmental effects in rocky mountainous areas in northern China

Based on observations of runoff plots and field investigations of gully cross-sections, impacts of various soil and water conservation measures on runoff and sediment yield are analyzed for different rainfall conditions. The results show that antecedent rainfall and rainfall intensity are the main factors affecting the runoff and soil erosion processes. Rainfall events with antecedent rainfall can produce high runoff and sediment yield. Large differences in the characteristics of two rainfall events will result in greater variations of total runoff and sediment yield from the same runoff plot. Under the same soil control measure and rainfall condition, soil and water conservation measures can reduce the impacts of antecedent rainfall and rainfall intensity on runoff and soil erosion. Among various measures, level terrace seems to be the greatest for soil conservation purposes. Combining with engineering measures,Vegetation measures is also effective in controlling runoff and soil erosion. In the initial stage of vegetation enclosure measures, engineering measure is necessary to improve the environment for ecological recovery. Gully head protection can control gully erosion effectively, but the effectiveness of gully head protection would be reduced when rainfall intensity increases. Therefore, the design of a gully head protection structure must be based on local hydrological conditions.