The Application Of MIKE21 In Flood Control In Western Mountainous Areas Of Beijing

The flood from western mountainous area has been dangerous to the central urban area of Beijing for years.The flood mainly reaches the central urban area through Beihan river,Nanhan river,and Yongding river water diversion channel.The flood on July 21,2012 was a disaster to Beijing.Therefore,the analysis of rainstorm flood mechanism in western mountainous area and flooding risk is necessary and will provide great support in flooding control to Beijing,especially the central urban area.This study included following parts:(1)Through investigation on rainstorm,flood and disaster conditions during rainstorm on July 21,2012,and analysis on the rainstorm flood mechanisms and flooding risk,the study provided support to flood control in western mountainous area.(2)It conducted 1D simulation of Beihan river,Yongding river water diversion channel and Kunyu section of Jingmi water diversion using MIKE11.Given designed inflow condition,the water level under different conditions was observed.It concluded that:under hundred-year storm,part of flood from upstream of Beihan river flowed into Qing river,the other part flowed into Xiangquan rotary island.The flood stopped at Wanan east road,without threatening the central urban area.Under condition of free control and flood diversion to north,the Nanhan river did not overflow,however,Yongding river water diversion channel and part of Yuyuantan overflowed.Only under condition of flood diversion to north,Nanhan river and Yongding river water diversion channel did not overflow,however,Kunyu section of Jingmi water diversion channel overlfowed.Under flooding control condition in Nanhan river,the flooding area in Nanhan river increased,however,Yongding river water diversion channel and Kunyu section of Jingmi water diversion channel did not overflow.(3)The study conducted 2D flood analysis on the Nanhan river watershed using MIKE 21,and simulated flooding area and depth of different conditions.Under hundred-year storm,the flooding area is 7.39km~2,and depth is 1.00 meter with no flood control in Nanhan river,with flooding area of 7.85km~2 and depth of 1.27 meter under flood control in Nanhan river.(4)Based on the analysis of flood risk in Nanhan river watershed,and the water level of both Yongding river water diversion channel and Kunyu section of Jingmi water diversion channel,the study concluded the plan in controlling flood from western mountainous area of Beijing,and provided guidance in alleviating the flood danger to central urban area of Beijing.This study can provide scientific support on the practice of western rainsotrm detention pond of Beijing.The method in analyzing flood risk could also provide support for flood forecasting in other areas of north China.