Elevation optimization model of flood control levee based on ecological resilience of riparian zone under climate change
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Abstract:
The construction of reinforced concrete levees damaged the resilience of the riparian zone to resist flood.It was also unable to cope with extreme flood disasters that exceeded the planned flood control standards under climate change conditions.Therefore,the traditional flood-control strategy by increasing the elevation of concrete floodcontrol levee was not the most effective way to solve the problem of urban flood control safety.It was urgent to establish an elevation optimization model of flood control levee considering ecological resilience of riparian zone,so as to provide decision support for the formulation of urban levee safety optimization scheme in the context of climate change. Aiming at the uncertainty in the elevation optimization model of flood control levee,an interval mixedinteger stochastic robust optimization model was established.The model could not only regulate the ecological resilience of riparian zone to resist flood,but also deal with the uncertainty of parameters in the optimal design of levee elevation.These uncertain parameters included the flood peak level in the form of the probability distribution function and the economic cost in the form of interval value.Besides,considering the dynamic change of riparian ecosystem resilience to flood due to the impact of climate change,binary variables were introduced into the model to indicate whether the restoration and reconstruction of the ecological riparian zone were necessary.Moreover,decision-makers could also make a quantitative tradeoff between system stability and economy by setting different risk parameters. The developed model was applied to three planned areas located on both sides of the urban river.Under the condition of the different flood peak levels and riparian ecological resilience,the optimal design elevation of the flood control levee was obtained.The result showed that when the value of the risk parameter was 0.5,the system cost was ［4.872,6.552］ million yuan.Before ecological reconstruction,the designed elevations of the flood control levees in the three areas were 118,［13.0,13.8］,13.9 meters,respectively.It could be seen that the impact of uncertain factors caused by climate change on the second region was more obvious.Affected by extreme flood disasters,ecological reconstruction was needed in the first area to increase the resilience of the riparian zone against floods when the flood level ranges from mediumhigh to veryhigh.Correspondingly,the levee needed to be raised ［2.8,3.5］,［3.5,4.0］ ，and ［2.8,3.5］ meters respectively.The situation in the second area seemed to be different.It only carried out ecological reconstruction at very-high flood level,and after the reconstruction,the floodcontrol levee in this area increased ［3.0,4.0］ meters.In addition,when the flood level was medium,high,and veryhigh,the flood overflowed the levee and submerged the third area.Furthermore,when the value of the risk parameter increased from 0 to 1,the system cost increased from ［4.809,6.437］ million yuan to ［4.926,6.656］ million yuan.At the same time,the stability of the model result was improved. It could be seen from the results that when the overall flood control capacity of the region was not enough to resist the intrusion of the extreme flood,the model would prioritize the allocation of excessive flood to subareas where the cost of flood damage was lower.Also,it must be recognized that there was a trade-off between system stability and economy.Therefore,in practical application,decisionmakers should comprehensively consider the extreme flood risk caused by climate change and the system′s resilience to resist extreme floods.Based on this,appropriate risk parameter values should be selected to control the proportionality of the optimization results,so as to obtain a better decisionmaking scheme.The results of the case showed that the model could provide decisionmakers with a reasonable flood control optimization strategy that considered the ecological resilience of riparian zones,and could provide a reference for the study of urban levee safety strategy under climate change.
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