| Recent years, in the status where the urban extreme climate increases and the urban surface which is more and more "hard" gradually replaces the original natural infiltration system, the waterlogging disasters have attracted frequent concern of the community. How could the city "escape" under so much flood-control pressure have already become a key problem to be solved. The key to prevent and control the city waterlogging is. the comprehensive and accurate simulation about its urban hydrology process. Based on the characteristics of rainfall and waterlogging in Xi’an, taking Qujiang New District as the research object, this paper respectively built a rapid assessment model of MIKE21 and a one-dimensional hydrodynamic network model of MIKE Urban to realize the fast recognition of the waterlogged area and the evaluation of current drainage capacity of the underground network. Last but not least, the waterlogging risk and water accumulation causes were analyzed through the waterlogging simulation by MIKE Flood coupling model under the situation of extreme rainstorm, and then the identification and optimization of the drainage bottleneck in the region were also achieved. The results of the study could provide a scientific basis for the prevention and mitigation, of urban disasters. The main conclusions were as follows:(1) The characteristics of precipitation in Xi’an were analyzed. The results indicated that the annual maximum rainfall of 24h of Xi’an station showed an increasing trend. The average rainfall in recent 11a was 601.9mm which was higher than the historical average of 556.5mm.July to September constituted the peak rainy months whose total rainfall accounted for 49.23%of the annual rainfall in Xi’an. The rainstorm’s occurrence reached a total number of 41 during 58 years with an average of 0.7 times a year in the Xi’an station. The seasonal distribution of daily rainstorm was similar to that of annual rainfall, but also happened in May to September.(2) Based on the model analysis, the rapid assessment of waterlogging in Qujiang New District was realized under different scenarios. The results showed that when suffered, an extreme rainstorm of 20-year frequency of 2h, the water depth of the region was given a priority to 0-0.05m under the two cases where the corresponding water accumulation area were 8.89km2 and 10.43 km2, respectively reaching a ratio of 87.20% and 87.9% of the total waterlogging area. The spatial distribution of the waterlogged region under two scenarios was consistent on the whole, which would not affect the rapid identification of the waterlogged area.Thus the influence of the spatial difference of surface runoff on the spatial distribution of inundated water could be ignored when constructing the fast assessment model.(3) The impact of building construction on the confluence flow pattern and the water accumulation in urban area were simulated and analyzed. The results showed that before the building construction, the confluence flow path was closed to the natural watershed morphology with an average length of 63m and the distribution of flow direction was more concentrated and consistent with a uniform flow as well. While after the building built, the confluence flow path was distributed around the outline of the building with an average length of 64m and the distribution of flow direction was more random with a relatively poor stability.(4) The drainage capacity of the current network in Qujiang New District was evaluated by the one-dimensional drainage pipeline model. The results indicated that the total length of drainage pipeline in this area was 63.93km, of which the pipeline whose drainage capacity was less than 1-year frequency reached 56.57km accounting for 88.49% of the total length, those between 1-year to 5-year frequency reached 6.43km, 10.06% and those more than 5-year frequency were only 0’92km,10.06% which were always some main pipes of large size. The drainage capacity of the current network in the region was at a poor level on the whole.(5) The comprehensive simulation of the waterlogging process of Qujiang New Strict was realized through the establishment of the coupling model of MIKE Flood. The results showed that when suffered an extreme rainstorm of 20-year frequency of 2h, the waterlogging risk of the region was given a priority to the moderate flooding where the water depth reached 15～60cm and waterlogging period lasted more than 30min. The waterlogged sites obtained from the model were consistent with the historical data in the location and depth of water accumulation, which qualitatively explained the reliability of the coupled model. The simulation results of the alleviating effect of pipeline expansion in the piece area where the pipeline drainage bottleneck existed on the waterlogging indicated that after the transformation,the maximum water depth of the piece area decreased by more than lm to below 0.5m.Although the severe flooding area significantly reduced compared to that of unreformed, the waterlogging relief was limited, which mean that green rainwater infrastructure should be combined to control it from the source to achieve the purpose of reducing the waterlogging risk. |
PDF Full Text Request