Research On Flood Control Optimization And Operation Of Longwangshan Reservoir Group In Xuyi County

With vast territory,complex terrain and diverse climate,China is vulnerable to water shortage,frequent floods and droughts.In order to reduce the losses caused by flood disasters,one of the effective measures to solve the problem is the optimal flood operation.Longwangshan Reservoir Group composes of Guiwu Reservoir,Shanhong Reservoir and Longwangshan Reservoir.The reservoir group is located in the southern hilly area of Xuyi County,Huai’an City,Jiangsu Province.The dam site is located in the middle reaches of Weiqiao River,a primary tributary on the south bank of the Huaihe River.The catchment area of the reservoir is 196.6km2,of which the catchment area of the upstream Guiwu Reservoir is 36.2km2,the catchment area of the Shanhong Reservoir is 15.4km2,the length of the main stream is 21.4km,and the gradient of the main stream is J=0.0015.The main functions of the three reservoirs are flood control and irrigation,combined with comprehensive utilization of aquaculture and tourism development.Longwangshan Reservoir Group protects 157000 people and 118000 mu of farmland.Xuyi County is located at the lower reaches of the Huaihe River,on the south bank of Hongze Lake.The terrain of the whole county is dominated by low mountains and hills.The terrain along the Huaihe River,lakes and the other rivers is low and prone to floods.According to the characteristics of the reservoirs of small watersheds in the plain area,this paper analyzed the natural geographical conditions and the current situation of water conservancy projects in the Weiqiao River basin,and studied the optimal operation of the combined flood of Guiwu Reservoir,Shanhong Reservoir and Longwangshan Reservoir.The main content is as follows:(1)The design flood hydrograph estimationIn the absence of measured runoff data,the "rainstorm atlas" is used to calculate the design flood hydrograph of Longwangshan reservoir group with 20-year return period and 50-year return period.(2)Construction of reservoir group flood joint optimal operation modelAccording to the characteristics of the hybrid reservoirs of Longwangshan Reservoir Group,the flood optimal operation model under the maximum peak clipping criterion is constructed.The minimum discharge under the model is the objective function,and the water balance,storage capacity,discharge and river flood routing rules are the constraints.(3)Solution of reservoir joint flood optimal operation model based on improved particle swarm optimization algorithmUsing an improved particle swarm optimization algorithm,the design floods with a 20-year return period and a 50-year return period are used as input conditions.To simplify the calculation process,the Guiwu Reservoir,Shanhong Reservoir,and Longwangshan Reservoir are divided into 35,33,and 40 time periods for calculation.The particle dimension is set to 108 dimensions,and the solution is encoded using computer programming language.(4)Comparison and analysis of the conventional and optimized operationsThe maximum discharge of reservoir,the maximum flood control storage capacity and the change of water level storage capacity during reservoir operation and the peak cutting rate of reservoir during optimal operation were selected as the criteria to evaluate the flood control function of reservoir,and the results of conventional operation and optimal operation were compared and analyzed.Due to the large flood control storage capacity,the peak clipping effect is the most obvious in Longwangshan Reservoir.The peak clipping rate of 20-year flood is 10.4%and that of 50-year flood is 13.5%during the recurrence period,which improves the safety of the protection objects downstream of Longwangshan Reservoir to a certain extent.In the process of optimal operation,the maximum flood control capacity occupied by the three reservoirs is smaller than that of conventional operation.The maximum flood control capacity occupied by the 20-year design flood of Longwangshan Reservoir is reduced by 16.1%,and the maximum flood control capacity occupied by the 50-year design flood of Longwangshan Reservoir is reduced by 15.9%,which ensures the safety of the reservoir itself to a certain extent.In the optimization operation process,the change process of reservoir water storage is more gentle,which slows down the phenomenon of steep rise and sudden drop of reservoir water level,prevents the change of groundwater dynamic field on the bank slope of the reservoir,and is more conducive to the safe operation of the reservoir.The optimal operation model of the hybrid reservoir established in this paper has certain effects on the safety of the downstream flood control objects,the safety of the reservoir itself and the safe operation of the reservoir,may provide a reference for the flood operation of the Longwangshan reservoir group.However,due to a large number of uncertainties in reservoir flood control operation,such as meteorological and hydrological factors,the risks induced by these uncertainties need to be further studied.