Charactors Of Deposits In Xibailian Watershed And Discussing On The Preventment Of Debris Flows In Beijing Mountain

Based on field investigation and historical data, this article studied characters of deposits in Xibailian Watershed and configuration, grain composition and changes of relief, act, trying to enrich theories on study of debris flow in Beijing Mountain and provide data to the mitigation of debris flow in Beijing Mountain.The research on characters of deposits in Xibailian Watershed shouws:(1) Lobate and sector shapes are the main deposit relief of debris flows in Xibailian Watershed. The longitudinal slope of deposits commonly is between 5° to 11°. And the cross slope of deposits is not uniform, between 11° to 32°. Each deposit configuration is different. And there are step relieves developed on the debris-flow deposits.(2)The common characters of deposits in Xibailian Watershed are: the framework of deposit is composed of gravels with or without crumb matters filled.Gravels of each deposit have big size, with average diameter from 0.21m to 0.8m, the biggest from 0.58m to 1.76 and the smallest from 0.1m to 0.42m.Granular analysis shows: ① average grain diameters change gradually small from upstream to downstream; ② Granular sorting in the whole watershed is poor, with the trend of increasing from upstream to downstream; ③ the grain skewness in the downsteam has a trend of more negative and coarsing than those in the upstream and midstream; ④ grain peakness of deposits wholly has a trend to normality, and increasing from the downstream to the upstream. And Wanghu Gully has a little different.(3) There is no distinct area relationship between deposits and gullys in Xibailian Watershed.Interaction influences exists between deposits and Xibailian main channel. Deposits change the channel way of the main Xibailian channel, and the Xibailian channel plays an important role on relief character development of depositDebris flows prevail in Beijing Mountain resulting from steep slops, geological structure, fractured lithesome and unique climatic conditions. According to statistics of data from 1900 to 2006, frequency of debris flows in Beijing Mountain changes periodically and it seems to increase after 1949. And another period is beginning now.Investigation shows:(1) There are many prolems in the mitigation of debris flows in Beijing Mountain: (1) new hazard zones turn up, including travel industry sites,breeding sites, new factories and new houses; (2) Some ole hazard zones remain safety incipient faults because of failed removal. Besides, decentralized responsibilities and limits of authorities of disaster administration branches, ineffective society mo bilization, etc. prevail and hinder the hazard prevention.(2) The conclusion shows that, new changes occurred in old hazard zones of flood and debris flow in studied hazard zones:① New hazard zones turn up, including travel industry sites,breeding sites, new factories and new houses;② Some ole hazard zones remain safety incipient faults because of failed removal;③ Some problems about the hazard regionliazation of loods and debris flows in Beijing Mountain exist; Besides, decentralized responsibilities and limits of authorities of disaster administration branches, ineffective society mobilization, etc. prevail and hinder the hazard prevention.(3) We can see for changes in studied hazard zones that new changes occur in hazard zones of flood and debris flow in Beijing Mountain, and give some advice for the mitigation of floods and debris flows in Beijing Mountain.Based on the idea "humanism design", this article presents the conception "escape passage against debris flow". It is defined by one escape passage through which local people or tourists can get to safe zones as fast as possible when debris flows occur. It consists of footpath and guiding signs.