Debris Flow Characteristics And Control Engineering Design Of Longtan Valley In Miyun Beijing

In this study,Longtan Valley in Miyun area,which was seriously affected by disasters,was selected as the research project.Through field investigation and laboratory experiments,the characteristic parameters of debris flow in Aiwa valley,Niujiao valley,Damu valley and Wangsi valley four debris flow gullies were analyzed and calculated.According to the typical design technical specifications of debris flow control engineering and local actual conditions,the debris flow suitable for the study area was constructed.In order to effectively control the potential hazards caused by debris flow in the basin,the system of measures for debris flow prevention and control should be designed and arranged accurately.The main conclusions are as follows:(1)The environmental background and formation conditions of four debris flow gullies were analyzed by means of field investigation and remote sensing interpretation.Digital elevation information in the gullies was extracted by combining Arcgis and BJGEMAP software,and the occurrence and development characteristics of debris flow in the gullies were analyzed.The results show that the total area of the four debris flow gullies in the study area is 1.71 km2,the total length of the gullies is 4.82 km,the average slope is 22.5 degrees,and the shape coefficient is between 0.24 and 0.41,which is conducive to the initiation and development of debris flow in the gullies.(2)According to the analysis of field investigation and laboratory experiments,the results show that the four debris flow gullies studied have more material sources and larger particle sizes,77cm,81cm,82cm and 48cm,respectively.The calculated volumetric weights of debris flows in four gullies are 1.55g/cm3,1.56g/cm3,1.55g/cm3 and 1.57g/cm3 respectively,which are dilute debris flows.The peak flow of debris flow in four debris flow gullies in 20 years is calculated by morphological investigation method and rainflood method.The results calculated by morphological method are slightly higher than those by rainflood method.In order to ensure the design safety,the results calculated by morphological method are taken as the design basis.Finally,the peak flow of debris flow in four debris flow gullies under rainstorm conditions in 20 years are 54.47m3/s,31.57m3/s,89.35m3/s and 69.48m3/s,respectively,the total amount of solid erosion of a debris flow is 1.60×104m3,and the total amount of a debris flow process is 4.45×104m3,which belongs to small debris flow.The maximum impact pressure of debris flow is 2.53t/m2,4.75t/m2,3.44t/m2 and 4.79t/m2,and the maximum impact height is 0.23m,0.44m,0.32m and 0.44m,respectively.(3)The overall planning and design of debris flow ditches are carried out according to the design criteria of once in 20 years and the check criteria of once in 50 years.A total of 12 sand-retaining dams with a total reservoir capacity of 5.67×104m3 were designed to meet the design requirements;the layout of drainage trenches,the selection of downstream natural trenches connected with Jiuhuang Road-main trench,a total of 400m drainage trenches;At the same time,in the upstream and middle reaches of each ditch with larger slope,the measures of closing hills and afforestation are implemented,and in the gentle slope and flat terraces,the terraces are renovated.