Extreme Precipitation Characteristics And Flood Warning Indexes In Qinghe Basin In Beiijing

The extreme precipitation events caused by the climate change frequently occur in the global scope.The urbanization construction of our country is risking to the disaster of flood control in the basins in cities.Rainfall runoff increase and runoff period shorten due to the surface of river basin hardening.It is difficult to quantify the early warning,resulting in flood response is not timely.The city needs to improve operational security.To improve level of flood control management,the research includes analysis of extreme precipitation events in basin,changes and influence of rainstorm,flood water level,flood dispatching,etc.each feature value,and a warning index system.The paper researches Qinghe basin which located in the north of Beijing City Center District by analyzing of extreme precipitation events characteristics and trends in order to get the extreme precipitation threshold of Qinghe basin with rainfall and flood data in 1986～2014.After quantitative analysis of land use types,topographic factors and flood discharge capacity,the MIKE FLOOD model is verified by historical flood data.With analysis of flood scenario matching precipitation andscheduling rules,the model is used to simulate the flood process in deferent flood scenario and quantify the relationship between the rainstorm,flood and flood risk in key sections.Then we get the flood warning indexes system with 4 levels,indicators,the flood risks and countermeasures and flood emergency response plan with 4 levels.,warning index and response plan is proved to be effect in actual flood control management with the application of "720" rainstorm flood in 2016The main conclusions are as follows:(1)The precipitation of>70mm can be considered as the extreme rainfall events in Qinghe basin.Extreme rainfall showed a downward trend in the total amount,the intensity and the number of days.All of the maximum rainfall among 1 day(Rx1d)and one among 5 days(Rx5d)and the rainfall intensity(SDⅡ)in flood season showed an upward trend in the upstream and a downward trend in the downstream.The average value of SDⅡ>11mm/d means a middle rain storm every in the flood season.On the whole,the Rxld and SDⅡ shows upper trend in the upper and a backward trend in the downstream.So there are more severe extreme precipitation events in the upstream than in the downstream.Qinghe river flood capacity is enough.While open discharge,daily extreme rainfall of 70～130mm can be discharged without flooding risk.(2)Warning index system of flood control in Qinghe basin includes rainfall,water level and flow rate.When the measured elements in the key section reached the standard,warn the corresponding level.There are 4 levels of warning:Blue warning:while average rainfall in Qinghe basin of 70mm,water level in Qinghe gate will be the standard of flood control level(37.7m)and the seeped areas will be near the Qinghe gate;Yellow warning:while average rainfall in Qinghe basin of 130mm,discharge in Shenjiafen gate will be the standard of limited discharge(316 m3/s)and everybody into the banks of river will be in danger near Shenjiafen gate and the seeped areas will be near the Qinghe gate too;Orange warning:while average rainfall in Qinghe basin of 155mm,discharge in Shenjiafen gate will be the detention standard of limited discharge(380 m3/s)and everybody into Shenjiafen detention will be in danger and Shenjiafen detention area shall be enclosed;Red warning:while average rainfall in Qinghe basin of 180mm,discharge in Shenjiafen gate is reaching No.2 level standard of limited discharge(450 m3/s)and everybody into Shaziying detention will be in danger and Shaziying detention area shall be enclosed and the seeped areas near the upstream will be seriously.The corresponding flood emergency response has 4 level of Ⅳ,Ⅲ,Ⅱ,Ⅰ,from low to high.The outline of flood emergency response plan is standards of administrative and technical rescue for controlling flood risk and social impact.It is proved that the parameterized MIKE FLOOD model is fit to the rainfall runoff and sediment yield in Qinghe basin with the analysis of the measured flood.The warning index system of flood control and the outline of response plan can be useful for warning timely and responding effectively.The research is an important technical support for the implementation of fine management and foundation for "river leads system".