| Losses caused by mountain torrent disasters in our country account for about 40%of the total losses from natural disasters,and mountain torrent disasters seriously limit the sustainable development of economy and society.The formation process of mountain torrent disasters is influenced by many complex factors,such as climate,hydrology,geology and so on,and mountain torrent disasters may have prompt ups and downs,fast velocity,and forceful destructive power.They are still difficult to manage in recent years.Therefore,research on spatial and temporal distribution characteristics of mountain torrent disasters,can provide scientific basis and technical support for the prevention of mountain torrent disasters,and has important theoretical significance and practical value.This thesis aims at the spatial and temporal distribution characteristics of mountain torrent disasters.The main contents and conclusions are presented as follows:(1)The temporal distribution characteristics of mountain torrent disasters:Firstly,the seasonal characteristics of rainstorm are studied.Based on the daily precipitation data of 673 precipitation stations in Chinese mainland,the 3 days Peaks Over Threshold sampling method,and two flood segmentation methods:the Probability Change Point and the Directional Statistics method are applied to segment the main rainy season respectively.Isoline maps are drawn to intuitively demonstrate the results of the seasonal characteristics in China.Results show that the main rainy seasons start earliest in the eastern region and gradually move to the northern region,and the end dates move from the eastern to the western area.Variation within a year in the northern part is greater than that in the southern coastal regions.Secondly,the existence of nonstationary in the main rainy seasons under the influence of climatic change and human activities is examined.Based on the daily precipitation data in 1952 to 2009 of Yichang precipitation station,the Annual Maximum sampling method,the trend test and the change-point test are applied to divide the the annual maximum series into two parts.The results of intraseasonal distribution,probability density estimation and the mean direction are obtained for the two parts.Results show that the main rainy season is moving backwards,and there is nonstationary in the series.Thirdly,the mountain torrent disasters in the history of Yichang are used to verify the reliability of the main rainy seasons.The results of the occurrence time,frequency and the proportion in the mountain torrent disasters,show that the the main rainy season results are reasonable.(2)The spatial distribution characteristics of mountain torrent disasters:The 35 mountain torrent disaster prevention objects in Xiaoting District in Yichang of Hubei province are selected as case studies.For each research object,with the disaster-causing water level from the field measurement results,the method of the adjustment of the stage-discharge relation based on the hydraulic radius is applied to obtain the disaster-causing discharge.And the adjusted discharge is compared with the discharge based on the Energy method.The Manning Formula method is applied to determine the stage-discharge relation in the control cross-section.Combined with the design flood results,the corresponding stage-population relation is obtained.Then the current flood prevention capacity is identified based on the frequency analysis accordingly.The administrative map of Xiaoting District is applied as the base map,and the current flood prevention capacity map is drawn to demonstrate the spatial distribution characteristics of 35 disaster prevention objects.Results show the spatial distribution characteristics in Xiaoting District as follows:in northwestern areas,most disaster prevention objects have a current flood prevention capacity of 5-20 years;in northeastern areas,most are less than 5 years;in southwestern areas,most are 5-20 or 20-100 years;and in southeastern areas,most are 20-100 years. |
PDF Full Text Request