As the era of the post-hydropower in China comes,the dam reconstruction works are increasing.In general,the river diversion for dam reconstruction consist of some original dam structures and some newly built diversion structures.Hence,compared to the diversion system for a newly built dam,the constraints and risk sources are more complicated in the diversion system for dam reconstruction.In this study,we will explored the risk evaluation of river diversion and the risk characteristics evolution rules.Based on the comprehensive analysis of diversion system for dam reconstruction,the main risk factors and risk modes were summarized,and the expressions of risk patterns were built.Those patterns included the upstream water level risk pattern,the downstream water level risk pattern and the discharge risk pattern.Then the multi-dimension risk discriminant was built on the ground of above expressions.Aiming at the flood uncertainty in the system,using the Copula function to describe the joint distribution of the flood peak and volume as well as taking account of the flow discharge rules and the operating regulation of discharge structures,the multi-dimension risk analysis model was built by sampling the flood routing,calculating hydraulic elements and integrating them into risk discriminant with Monte-Carlo method.The qualitative analysis showed that the above risk patterns were not fully correlated because of the differences in function and design standards of diversion structures,and the risk ruled by multi-dimensional distribution.Since the risk feature was decided by specified configuration,a typical case was provided,which used the original dam as upstream cofferdam and blocks the discharge way as construction pit.The quantitative risk analysis showed that there was a dominant risk pattern shifting point,beside which the discharging risk pattern took over downstream water level risk pattern as dominant risk pattern.The driving factor was the discharge rate of diversion system,and the shifting point corresponds to the upper risk limit that downstream cofferdam could defend.The research can serve as references for diversion risk evaluation and diversion scheme optimization for a dam reconstruction.
