| With the rapid development of economy and society,the uneven distribution of water resources in time and space does not match with the new development concept,which seriously restricts the development of China.As an important strategic tool for national water management,The Interconnected River System Network(IRSN)plays an important role in optimizing and coordinating the allocation of regional water resources,improving the ecological environment of rivers and lakes,and resisting water and drought disasters.However,due to its unique vulnerability,it is often accompanied by potential risks such as flooding and water ecology,so it is especially important to give full play to its positive effects and reduce negative impacts,as well as to analyze the risks associated with IRSN.Based on the complexity of IRSN,the multidimensional nature of the connection,the randomness of the connection associated risk and the universality of the flood disaster,how to identify and quantitatively assess the risk of different types and scales of IRSN,establish the management mechanism of IRSN associated risk in response to the extreme hydrological events,and develop the adaptive countermeasures of the river-lake system connection associated risk under the changing environment,will become the river-lake system connection associated risk management.It will become an important research content in the control of risk associated with river-lake system connectivity.As a large water saving unit in IRSN,the geometry of the regulation and mitigation of the risk associated with the water system linkage project is worthy of our in-depth discussion.In this study,Yishusi IRSN in the downstream of the Yishushi River system in Shandong Province of the Yishushi Basin was selected as the research object.In this IRSN,the Pichang floodway was dug in 1958 to connect the Yi River with the Middle Canal;the Xinyi River was dug in 1949 to receive water from the Luoma Lake and the old Shu River and then converge into the Yellow Sea.Therefore,based on the hydraulics model and considering the flood correlation of different rivers in the connected river network,an analysis model of the risk associated with the connected river and lake systems under stochastic water conditions was created.By fitting the edge distribution and correlation construction of the identified random variables,the random combination of water conditions is used as the boundary conditions of the simulated working conditions.Meanwhile,the risk analysis model is used for flood risk simulation calculation to obtain the risk probability and risk intensity in three aspects of flow,water level and flow velocity of the main river within the water system,and analyze the law of flood risk change under different risk scenarios.In addition,in order to effectively reduce the risk of associated flooding in the downstream of the Yishu River system,the targeted control measures of the hydraulic regulation of Lake Luoma are proposed,and the effect of risk avoidance and the influence law of the hydraulic regulation of Lake Luoma on the risk of associated flooding in the connected river-lake system are initially analyzed.The results of the study are as follows:(1)A model is developed to analyze the risk of IRSN under stochastic water conditions by combining Vine Copula function and one-two-dimensional coupled hydrodynamic model.The hydrodynamic model is calibrated and calibrated according to the hydrological data obtained.The results show that the MAE and RMSE are lower than 0.45 m,and the NSE is greater than 0.85.The model simulation effect is good.(2)The Vine Copula function is used to establish the marginal distributions of random variables.The best-fit distributions of the flood peak flow of Hanzhuang Canal and the flood peak flow of the lower reaches of Yi River are both Weibull distributions,and the best-fit distribution of the flood peak flow of the Old Shushi River is a lognormal distribution.Frank Copula is used for the flood peaks of Hanzhuang Canal and Lower Yi River,and Clayton Copula(270 degrees)is used for the flood peaks of Hanzhuang Canal and Old Shu River;Normal Copula is used for the second level tree,and the p-value of Vine Copula is 0.55(greater than 0.05),which pass the goodness-offit test.(3)The risk analysis model is used to quantitatively assess the risk associated with the connection of different risk sources.The results show that Hanzhuang Canal and the Middle Canal section are at low risk,Xinyi River is at medium risk under the risk source(1);under the risk source(2),Hanzhuang Canal and the Middle Canal as a whole are at low risk,the whole section of Xinyi River is at low risk;under the risk source(3),Hanzhuang Canal is at low risk,and the risk of the Middle Canal is elevated to medium risk,and the whole section of Xinyi River is at high risk.When the flood recurrence period is raised to one hundred years,the whole area rises to high risk except Hanzhuang Canal.(4)After the regulation of Loma Lake,the risk probability of Xinyi River flow is reduced by about 10% and the risk intensity is reduced by about 16%,and the whole section is still in medium risk under the risk source(1);under the risk source(3),the risk probability of flow from Zhangshan Gate to Koutou is reduced from 0.63 to about0.5,and the risk probability of flow from oral to Haikou section is reduced from 0.8 to0.5,and the risk intensity of the whole section is reduced by about 80%,and the risk level is reduced from high risk to medium risk.When only the upper reaches of the Yishu River system experience a 100-year flood with a recurrence period,the flood risk probability at Shuyang Station of the Xinyi River decreases from 0.8 to 0.6,and the risk intensity decreases from 0.42 to 0.26,from high risk to medium risk.(5)Through lake hydraulic regulation,it is found that part of the downstream river cross section is out of the risk zone and enters between the risk zone and the safety zone before regulation,which is referred to as the buffer zone in the paper.This area,through certain lake regulation,raises the safety threshold of water depth of the downstream river from 9.7 m to 10.3 m,an increase of 6%,and the safety threshold of flow velocity from 0.8 m/s to 0.93 m/s,an increase of 16%.It breaks through the limitation of a single risk safety threshold in the original river-river connectivity study and makes the risk control more flexible. |
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