Improvement Of Hydraulic Regulation On The Accompanied Water Environmental Risk In The Interconnected River System Network Of Plain Areas

As an important strategic means of water control and use in China,the Interconnected River System Network(IRSN)plays an important role in optimizing the temporal and spatial allocation of regional water resources,restoring the natural appearance of rivers and lakes,improving the water ecological environment,and enhancing regional competitiveness.However,as a complex system engineering,the IRSN will inevitably be accompanied by a series of potential risks while changing the original water system pattern to meet the needs of human social and economic development.Especially for the plain river network areas with dense population,industrial and agricultural agglomeration,and many pollution sources,a series of IRSN projects in the process of urbanization destroyed the original river structure,changed the natural flow direction of the water body,and restricted the continuity of river and lake water system in the basin.Therefore,IRSN has become an important factor interfering with the water environment quality of the plain river network area.Based on the one-dimensional hydrodynamic water quality model,a water environment risk analysis model based on catastrophe theory random forest is established.By considering different combinations of water diversion conditions,the risk scenario simulation scheme is formed,and the calculation method of water environment risk level of the plain river network is put forward.Based on the model,the risk intensity and risk probability distribution of each scheme group is obtained,and the water environment risk associated with the connection of the plain river network in Changzhou district is quantitatively analyzed.Evaluate the avoidance effect of water environment risk under different water environment risk control measures,and determine the optimal risk control scheme formed by the combination of different diversion conditions,so as to provide a reference for the comprehensive treatment of water environment in plain river network areas.The results are as follows:(1)Proposing the risk analysis model of the accompanied water environmental risk in IRSN by the coupling method of catastrophe theory and the random forest;The risk analysis model of the plain river network in Changzhou City is established and verified.The simulation effect of the model is good,and the calculation results are reasonable and reliable.(2)By considering the combination of diversion conditions such as different diversion paths,diversion flow,diversion water potential,and diversion time,the water diversion scheme is formulated as the risk scenario simulation scheme.Based on the water environment risk index calculated by the risk analysis model,a risk classification method considering risk probability and risk intensity is proposed.(3)Based on the risk scenario simulation scheme,the water environment risks of each simulation scheme group under three different diversion paths: self-drainage scheme,East hub pumping scheme,and Cailing port pumping scheme are analyzed respectively.The risk intensity and risk probability distribution results show that the concentration of water quality index decreases to a certain extent under each pumping and drainage scheme;Under the pumping and drainage schemes of East hub and Cailing port,the risk intensity and probability are significantly lower than those of self-drainage scheme due to the pumping effect,but the improvement effect of Cailing port pumping and drainage scheme on water environment risk is slightly;The environmental risk intensity and risk probability of each scheme decrease with the increase of diversion flow and diversion duration,and stabilize when the diversion duration is 3 days.It is determined that the appropriate diversion time is 3 days.(4)Taking different combinations of diversion conditions as water environment risk control measures,this paper discusses the avoidance effect on the water environment risk.The results show that the water environment risk level decreases with the increase of diversion flow,and under the condition of constant total diversion flow,increasing the diversion flow of Zaogang River can reduce the water environment risk in the main urban area;Under different diversion paths,the pumping and drainage scheme of the East hydro project is more in line with the drainage water potential;Under different diversion water potentials,the water environment risk in the main urban area can be effectively reduced when the overflow weir is adjusted to control the urban water level of Zaogang River to reach 4.00 m.Therefore,the most suitable water environment risk control measure is that the diversion time is 3 days,diversion path is(1)＿WR＿2,diversion flow is(2)＿WQ＿4,and diversion water potential is(3)＿WP＿5.