Research On Causations Of Flood And Waterlogging Disaster Of Water System In Fuzhou City And Its Improvement Countermeasures

Along with the explosive expansion of urban area and the increasing frequency of extreme weather events, the urban flood disaster is increasingly frequent, especially in the city located along tidal estuary. In this dissertation, according to the runoff processes from diverse sub-basins in northern mountain area and the flood water discharge processes out each urban drainage pipeline in term of four design rainstorm criterions, a numerical simulation model of flood control and drainage of it is established in allusion to the city at tidal estuary, by which the capacity of flood discharge and waterlogging drainage of the status quo is evaluated and the causes of flood disaster is revealed by the annlysis of the hydrodynamic characteristics of the river network within the main city. On this basis, flood control strategies are proposed matched with different design rainstorm conditions. In addition, the encounter risks of rainstorm and tidal level which are the most main factors resulting in the disaster are analyzed with copula fuction, and the risk of this disaster is calculated. This research mainly includes the following aspects:(1) According to the water system information, a numerical simulation model of flood control and drainage is established with HEC-RAS software, and then the model is verified with the rainstorm data, flood control operation data and the flooding area during Typhoon “Longwang”.(2) The capacity of flood discharge and waterlogging drainage of the status quo is evaluated by simulation flooding routing on four design rainstorm conditions. Results show that the discharge capacity of water system in Fuzhou city is unable to reach once in 5-year design rainstorm criterion.(3) The hydrodynamic characteristics of the water system within the main urban area of the city are analyzed by the simulation of flood processing on the rainstorm with 5-year return period, in which the main causations of the disaster are respectively revealed from four factors—insufficient storage and detention of flood, low flow rate of rivers, lack of unit capacity in pumping station, and massive flow invasion from northern mountain area.(4) In light of the dominating causes of the disaster and the reality in Fuzhou city, the corresponding regulation schemes are put forward for different design rainstorm criterions, and advantages and disadvantages between the schemes are compared and analyzed. Then, some schemes are proposed: the "regulation and detation" plan is offered to make the drainage capability of water system meet the requirement of discharge the flood result from the rainstorm with 10-year return period in fuzhou city; and the "regulation and detation and distribution" project is advised for flood drainage on the rainstorm with 20-year return period, and for the rainfall with 50-year return period "regulation and detation and obstruction" plot is recommended. Base on this, the whole schemes combined non-engineering countermeasures are presented: "whole plan, implement step by step, engineering and non-engineering measures combined".(5) Encounter risk and joint risk of rainstorm and tidal level are analyzed by the model with copula function on various conditions, the result show that the encounter risk probabilities of the design rainfall with 50-year return period and the various tide level are no more than 0.150%; and with 20-year return period are no more than 0.242%; and with 10-year are no more than 0.344%; and with 5-year are no more than 0.502%. Then the risk probability of the disaster of flooding and waterlogging is no more than 5.595% calculated referring to improvement schemes on rainstorm with 20-year return period, which proves that the tidal level condition chosen in the dissertation is reasonable.