| Debris flow is a natural geological disaster with complex causes,suddenness and great harm.Historically,there have been many serious debris flow disasters in the mountainous areas of Beijing.The shizisigou Watershed is located in the southwest of Fangshan District,Beijing.Due to the heavy rainstorm on July 21,2012,a certain scale of debris flow disaster broke out in the gully area,which seriously threatened the life and property safety of the residents downstream of the gully mouth and caused certain damage to the public building facilities in the scenic spot.Based on previous data collection and field investigation,this paper comprehensively and deeply analyzed the formation mechanism,inductive factors,provenance distribution and gully development characteristics of debris flow disaster in the shizisigou Valley.And with the help of the FLO-2D platform,it is numerically simulated under three different rainfall frequencies,and finally the risk zone map is obtained,and the proportion of different risks is calculated.At the same time,in order to effectively prevent and manage disasters,under the principle of adapting measures to local conditions and comprehensive management,a set of debris flow prevention and control measures system that is most compatible with Shizisi Valley has been accurately constructed.The main work and research conclusions are as follows:(1)Firstly,the high-precision DEM data in the research area was obtained with the help of Arc GIS platform,the number of water gathering points was determined and the optimal location was selected according to the site selection principle.and calculate the necessary parameters such as clear water,debris flow process lines and Manning coefficient under different rainfall cycles.In order to simulate better.Finally,the risk zoning chart is obtained and the proportion of different risks is calculated.(2)On the basis of on-site field survey,combined with remote sensing interpretation and related specifications,calculated by empirical formula method,rain flood method,pentagonal correction method,etc.:Shizisigou ditch area is 4.4km~2,and the main ditch is 3.48 in length km,the average slope drop is 248‰,and the volume density of debris flow is 1.57g/cm~3,the flow rate of the debris flow in 20a is 30.52m~3?s,the total amount of debris flow washed out at one time is14800 m~3,and the total amount of solid matter washed out of the debris flow is 5100 m~3,it is a rare debris flow,and the scale of the explosion is small.(3)According to the actual topography of the study area,a combination of engineering and biological measures was used to prevent and control the debris flow disasters in Shizisi Gully.Taking the 20-year return period rainfall frequency as the design standard and the 50 year return period rainfall frequency as the check standard,three gravity sand retaining dams are set up in the upper,middle and lower reaches,with a total storage capacity of 21900,meeting the use requirements.In order to discharge the debris flow in time,a drainage channel with a total length of about 50 is arranged at the mouth of the ditch;measures such as sealing the upstream section of the channel and re-rectifying the downstream terraces,the total investment of the prevention and control engineering system is estimated to be 386570 yuan. |
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