Evaluation Of Debris Flow Control Effect In Yuanmou County Of Yunnan Province

Yuanmou County is located in the northern part of Yunnan Province.Yuanma Town,the county seat,is located in the Yuanmou Basin.Dongshan County is a high-mountain mountainous landscape in the eastern part of the county.The valley is deep and the debris flow develops.A total of 8 debris flow ditches were developed near Yuanmou County's urban areas.Debris flows of different sizes occurred in the history of 8 mudslides,which caused serious damage to the urban areas and surrounding villages.Therefore,Yunnan Province has carried out comprehensive treatment projects for key towns and geo-hazards,but whether or not the treatment project achieves its objectives has threats to the planning area of the county and surrounding villages,and it is necessary to evaluate the effectiveness of the treatment projects.The evaluation results will be used to prevent and mitigate debris flows.And follow-up governance provides the basis.Based on the basic features of mudslides and on-site surveys of treatment projects,this paper further analyzes the formation conditions,development characteristics,historical evolution,and treatment engineering status of debris flows,qualitative evaluation through field investigations,reduction of source benefit analysis of treatment projects,and FLO-2D-based software.Three methods of numerical simulation before and after the treatment of debris flow were comprehensively evaluated for the effect of debris flow control in Yuanmou County,and the following results were achieved:(1)Debris flows in the study area are all gully-type debris flows.The Dagu River and the control ditch are large-scale large mud-ditches,which are located at both ends of the study area,and the remaining six are interspersed between the two ditch slopes.In the area,among them,except for Modanggou,which is a large debris flow ditch,the rest is small and medium-sized.The Dagu River is mainly sourced from slope erosion sources and channel accumulations.The source of the control channel is mainly the source of the upstream slippery slip and a large number of channel sources.The source material in the middle area of Dongshan is mainly the source of slope erosion and collapse.According to the deposition characteristics of debris flow in the Mizoguchi,mudslides of various sizes in the geological history of various debris flow ditches have emerged.The current ditch also has conditions for the formation of large-scale mudslides,and it is possible to predict the possibility of large-scale mudslides in mudslides in the region.(2)The operation status of the debris flow control project in the research area is relatively good,the qualitative analysis and control effect is in a good level,and there are local deficiencies.The governance of Dagu River and Gyangyanggou needs to be improved.Blocking direct benefits includes intercepting sediment,flood discharge,controlling the amount of solid material recharge,and preventing undercutting of the trench.The sand blocking dams play a major role in the interception.The number of valley workshops also plays a significant role.The indirect benefits of blockage in the area include intercepting silt,stabilizing the gully bed and slope,reducing the peak flow of debris flow,reducing the severity of debris flow,changing the nature of debris flow,and improving the ditch erosion reference surface of the upper reaches,reducing the erosion rate of the channel.The efficiency of the source-reserving of the stability-retaining slopes of the bar-dams is between 0.472%and 37.52%,the benefit of the Gugou dam is 0.64%-7.80%,and that of the solid-bed dam is 0.55%-4.74%.After the treatment,due to the increase of vegetation,the erosion of loose solids was reduced by 1152.12×10~6m~3,a decrease of 31.82%,and the biological engineering control effect was significant.(3)Based on the FLO-2D software,the numerical simulation of 8 debris flows in the 20,50,and 100-year rainfall conditions.In 20 years,the total accumulated fan area was 457,1619.5m~2,and the total ejected mass was 71.19×10~4m~3;in 50 years,the total accumulated fan area was 11670633.5m~2,and the total ejected mass was99.91×10~4m~3;100 years In one case,the total accumulated fan area was16756888.1m~2,and the total ejected mass was 139.16×10~4m~3.The accumulation character was characteristic of a dilute mudslide.(4)Considering the treatment project,the numerical simulation of 8 dam-flow ditches was carried out.Under the three different rainfall frequencies,the total amount of debris flow out of mudslides was relatively low by 58.44%,32.70%and 28.27%,respectively.It shows that the governance project of the Yuanmou County government on the 8 mudslides in the Yuanmou County plays a significant role in the disaster reduction effect.(5)According to the mud depth(H)of simulated debris flow and the depth and speed(VH)of mud depth,the intensity map of debris flow is divided,and the dangerous area map of debris flow is shown in combination with the frequency of outbreak of debris flow.The high risk of mudslides after treatment compared to pre-governance is reduced by 71.34%,45.62%,and 44.24%,respectively,in 20 years,50 years,and 100%rainfall.The high risk range of mudslides was less than 75.16%,63.74%,and 61.30%at the three frequencies,respectively.It shows that the implemented governance project has achieved a good control effect.The evaluation of the debris flow control project by field qualitative evaluation,benefit calculation of debris flow control and numerical simulation before and after treatment shows that the effect of the treatment project is obvious.However,after the current treatment,the local hazards are in a high state and the treatment engineering measures are different.To a certain extent,there is a situation of destruction and obsolescence.Therefore,it is necessary to further control the debris flow in Yuanmou County.The research results of this thesis can not only provide strong support for the theoretical guidance and practical application of the debris flow disaster warning and prevention work in Yuanmou County,but also provide reference for the evaluation methods and system of the treatment effect of mudslides in mountainous towns.