| Environmental flows play an important role in maintaining the ecological integrity and biodiversity of rivers.They are key factors that affect the health of river systems.Appropriate environmental flows can effectively protect rivers and surface environments.The construction of large-scale dam projects and artificial river courses has brought benefits to the society and economy on the one hand,and caused many problems to the ecological environment of rivers on the other.An increasing number of people are aware of the important impact of environmental processes,including seasonal and predictable flows,on rivers and associated floodplains and wetlands.Taking the control area of the middle reaches of the Fenhe River as the research object,this paper discusses the evolution and continuous process of the runoff in this area in many aspects.Based on the traditional Tenant method,the improved Tenant method with seasonal modulus is proposed,and the influencing factors of the water quality change are simulated.The environmental flow control and water diversion schemes at different levels are given.The main tasks include:(1)Research on runoff and water quality change rule in gate control areaBased on the 1980-2015 year runoff data of Fenhe two dam station and Yitang Station,the trend and continuity of annual runoff in the sluice controlled area were analyzed by Kendall rank correlation test and R/S analysis method.The runoff evolution law was studied by means of travel analysis,and the annual runoff of 2011-2015 years was predicted by BP neural network and exponential smoothing method and compared with the measured values.The results showed that the annual runoff of the two dam stations in Fenhe River showed a non significant rising trend in general,and the future had a positive persistence,and the overall rise trend of Yitang Station showed a significant downward trend,The probability of both stations'continuous abundance,flatness and continuous loss decreases with the increase of consecutive years;and the application of exponential smoothing method was predicted for 2016-2020 years of the Fenhe two dam and Yitang Station.The average annual runoff is 294 million 300 thousand m~3 and 407 million 520thousand m~3 respectively.The most serious pollution is total phosphorus and total nitrogen,and the size of environmental flow has a significant impact on water quality.(2)Study on target value of environmental flow in sluice controlled areaThe traditional Tennant method can not express the changing trend of the environmental flow between the years and the season,and can not reflect the actual situation of the Fenhe River.Therefore,the average annual flow rate is replaced by the typical annual flow,and the more suitable staging percentage is chosen,and the substantial improved Tennant method is used to calculate the environmental flow of the middle reaches of the Fenhe River.The results show that the minimum,suitable and optimum environmental flow rate of the two dam station of Fenhe River are 1.91m~3/s,4.63m~3/s and 8.43m~3/s,and the Yitang Station is 2.16m~3/s,6.47m~3/s and12.93m~3/s.(3)Factors influencing water quality and water quality in gate control area and regulation of annual environmental flow at different levelsThrough numerical simulation,the change process of water quantity and water quality of river under different water conditions and gate opening degree is analyzed.It is found that the influence of the construction of sluice dam and the opening degree of the gate on the COD is the most significant.For different levels of years,the corresponding regulation and water transfer plan is formulated.The results showed that the regulation of accumulation and supplement was the best for the target value of environmental flow.The annual water year,the flat water year,the dry water year and the special dry year meet the environmental flow target value of 62 million 392thousand m~3,135 million 198 thousand m~3,154 million 566 thousand m~3 and 40 million 36thousand m~3,respectively.The research results can provide theoretical basis for sustainable development and scientific management of water resources in the middle area of Fenhe River. |
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