Study On Urban Flood Control Model Based On The “Water-logging Points”

Increasingly serious urban flood disaster has become one of the important problems that can not be avoided in the construction and development of urbanization in China. However, China’s urban flood control theory system is imperfect at present, and its weak flood control facilities system also has been unable to meet the requirements of flood control capacity of the urban development. So, in order to improve the theoretical system of urban flood disaster prevention and control, it is necessary to put forward a more scientific and rational urban concept of flood control and flood control mode in view of the characteristics of urban flood disaster.Based on the calculation model of urban rain flood in previous studies,according to the storm disaster in the city, based on the following basic facts: it is not equal to all areas of the city will form a "flood disaster" in a rainstorm which exceed the standard; it may also form a “flood disaster” in some areas of a city in a heavy rain which does not exceed the standard; the so-called“flood disaster” should refers to be submerged area “loss”, and the loss can be tangible and quantifiable economic losses, may also is the invisible social loss,but which determines the size of the loss should not only the region of the submergence depth, at least contains of submerged water evacuation duration.According to this, it proposed a new city flood control concept of the key prevention in the “Water-logging Points” in this paper, and carried out a study on urban flood control mode based on the “Water-logging Points”, and obtained the following main research results:(1) Analysed the problems of urban flood control in our country,combined with the characteristics of urban flood disasters, it pointed out that there were some defects in normative documents on the maneuverability of setting the standards of flood control facilities by its level or type and put forward a new urban flood control concept of the key prevention in“Water-logging Points” to supplement the existing normative documents, so as to provide a strong guidance for the construction of urban flood control in China.(2) On the study of the domestic and foreign urban surface runoff and confluence calculation model, combined with the characteristics of urban runoff and confluence, it attempted to combine the Comprehensive Runoff Coefficient Method and the Initial Loss after Loss Method to calculate urban average surface runoff; and for the calculation of the surface confluence, it proposed viewpoints on Isochrones of the urban “Water-logging Points” based on the principles of Isochrones of the basin, and established an Improved Isochrones Method, which made the calculation of urban surface convergence is more in line with the practical application thanks to mainly considering the“urban surface convergence loss”.(3) For the calculation of the “urban surface convergence loss”, this paper proposed the effective coefficient of the comprehensive interception of rain water gully to calculate the effective intercept flow, and then calculate the loss amount of urban surface confluence, wherein the effective coefficient of the comprehensive river closure of rain water gully is multiplied by the two part of the interception coefficient of rain water gully and the interception efficiency of rain water gully.(4) On the basis of the above research, it established urban flood control mode based on the “Water-logging Points”, and the main components of the mode are as follows:(i) The definition of urban “Water-logging Points”. According to the defects in the definition of urban waterlogging of the “Outdoor Design Specification <GB50014-2006>”(2014 modified version), it studied and pointed out that the city waterlogging problem involves double contents:waterlogging depth and duration. In consideration of the inundation loss, under the conditions of the design rainstorm, when a point area of the city of waterlogging depth and duration more than the threshold, then we can say here waterlogging caused by rainstorm and the flooded area is defined as the urban“Water-logging Points”.(ii) The research value of the “Water-logging Points”. According to the aforementioned analysis on the characteristics of the city rainstorm disaster and the definition of the “Water-logging Points”, combined with China’s urban flood control and drainage engineering system, it can be seen complete the transformation, the replacement of a city’s drainage pipe network and engineering system in a short period of time is not realistic. Therefore, The research value of the “Water-logging Points” to provide new theoretical support for the definition of urban waterlogging, bring new ideas for urban flood control and drainage, provides a new research direction for the standard of city flood control and urban flood control for measures and provide decision basis for the targeted measures and schemes for urban flood control.(iii) The urban water calculation based on the single “Water- logging Point”. it included the calculation of urban surface runoff, the calculation of urban surface convergence, the calculation of “urban surface convergence loss”, the water depth calculation of urban “Water-logging Points” and the water storage time calculation of urban “Water-logging Points” and so on.(iV) The urban water calculation based on multiple “Water-logging Points” under mixed coupling modes. There are a lot of “Water-logging Points” according to the actual situation of the city, which can be regarded asmicro reservoirs, and these micro reservoirs form a reservoir group system through the road in series, parallel and hybrid form, and each micro reservoir has storage function for that of geographical downstream location. Therefore,on the basis of the urban water calculation of single “Water-logging Point”, it added the calculation of “Water-logging Points” runoff storage time, and the water calculation in the lowest geographical position.(V) The urban waterlogging disaster judgment based on the“Water-logging Points”. According to the new definition of urban waterlogging,it calculated the maximum water depth and duration of the “Water-logging Points”, and then established the urban waterlogging disaster judgment formula. It proposed that when a point area of the city of water-logging depth and duration more than the threshold, then we can say here waterlogging caused by rainstorm.It took Taiyuan University of Technology West Campus as test area and twice typical rainfall process in Taiyuan as examples separately to verify and apply the urban water calculation model based on the “Water-logging Points”,and compared with the date measured water depth and the water storage time.It showed that: calculation results by the usage of the model was consistent with the measured data on the same day, thus the rationality of the model was verified by the result.Research achievements of this paper can not only provide new theoretical support for the definition of city water-logging, but also can provide a new idea for the idea and model of urban flood control; it does not only have wide application prospect and practical promotion value in urban flood control and disaster reduction, but also has an important reference value for the development of the urban flood safety plan, renovation of city drainage system and the assessment of the urban submerged loss.