Break Risk Assessment Of Check Dam System By Flood On The Loess Plateau

Check dam is a defender of basin’s comprehensive governance system.It not only can store the flood sediment in place to effectively prevent soil erosion and reduce downstream flood risk,but also can form dam land to make full use of water and soil resources by blocking,storing and silting.However,the operation risk of check dam increased with the extension of operation time,causes the dangerous happened frequently.In addition,under the influence of climate change in recent years,the frequent occurrence of sudden heavy rainfall has further increased the flood risk of check dam.In this paper,the study object is the Jiuyuangou-Basin on the Loess Plateau.Through data collection,hydrology statistics,numerical simulation method,etc.,to simulate the process of check dam system by flood,reveals the break risk of check dam system by flood on the Jiuyuangou-Basin.The main conclusions are as follows:(1)The analysis of hydrological evolutionary laws reveals the laws of hydrological change and relationship evolution of the basin,which not only reflects the trend of rainfall and runoff decline year by year in the Jiuyuangou-Basin,but also reveals the significant role of check dam construction on soil erosion in the basin.The results show that the average annual rainfall in the Jiuyuangou-Basin is 354.4 mm,the rainfall during the flood season accounts for 89.1% of the annual rainfall,and the distribution of rainfall during the year is extremely uneven;while the runoff during the flood season accounts for only 56.3% of the annual rainfall,indicating that the water conservation measures such as the check dam project have a significant effect on flood interception during the flood season;after the adjustment of the layout of the check dam system in 1977,the average annual sand production decreased by about 21 times,with significant results;the continuous rainstorm process in the Jiuyuangou-Basin is mostly concentrated within 6 hours,so the analysis of the maximum 6 hours rainfall frequency can reflect the design rainfall characteristics of the Jiuyuangou-Basin and provide a theoretical basis for the later analysis.(2)The dynamic simulation of check dam system outburst process is of great significance to the risk analysis of check dam system.The coding and classification of check dam system can clarify the topological relationship of check dam system and is the basis for the simulation of check dam system flood outburst process.The results show that: the check dams in the Jiuyuangou-Basin can be classified into 9 grades;the check dams that can withstand rainfall in 20,50 and 500 years are 68.5%,45.2% and 35.6% respectively;after heavy rainfall,about 19.2% of the check dams collapse within 20 min,about 42.6% of the check dams collapse within 180 min,accounting for 62.2% of the collapsed check dams;most of the check dams are difficult to withstand 3 hours of continuous heavy rainfall;the increase in rainfall not only increases the number of collapsed dams in the basin,but also accelerates the collapse time of check dams;heavy rainfall is one of the main sources of check dam risk.(3)Flood inundation losses of check dam system are one of the important indicators for quantitative assessment of flood risk in check dams.The results show that the socio-economic losses caused by rainfall in 5,20,100 and 500 years are 312,000,510,000,583,000 and 665,000 yuan,and the eco-environmental losses are 190,000,311,000,356,000 and 406,000 yuan respectively.The increase in rainfall has led to a significant increase in the losses,threatening the safety of local people and their property,and undermining the harmony of the ecological environment.There was more loss in Longwangmiao dam,Jiuyuan dam,Mazhangzui dam,Fanshanda dam,Laolimao dam,Pujiawa dam,which should be put more key protection.(4)The extraction of check dam flood risk factors,the construction of risk indicator systems and the calculation of risk indicator weights are important elements in the evaluation of flood outbreak risk in check dam systems,and are necessary processes for the quantitative analysis of the level of risk in check dam systems in catchments.The results show that: the risk of flooding in the check dam system can be divided into 4 primary indicators and 12 secondary indicators;24.7% of the comprehensive risk of check dams in the Jiuyuangou-Basin is very dangerous,72.6% of the comprehensive risk of check dams is mild,and 2.7% of the comprehensive risk of check dams is basically safe;for all primary risks,the engineering risk is more evenly distributed,the environmental risk is generally large,the risk of loss is more concentrated,and the management risk is generally more serious;Therefore,in the future,when reinforcing,eliminating the risk and building new check dams,should put special emphasis on its management,to strengthen the emergency and early warning of risk,and accelerate the improvement of check dam management system,especially in crowded areas,should take strong measures to promote the risk of check dams to disperse and transfer for ensuring people’s life and property security.