| The development of social economy has promoted the process of large-scale urbanization,but it has also created many problems and challenges.The expansion of"impervious surface",the increase of water use to exist and produce and sewage discharge in cities have led to the growing shortage of ecological water in rivers near cities,especially those with water shortage,high pollution and high sediment concentration.The impact of urban construction on ensuring the river's ecological base flow,which is the minimum flow that maintains the basic ecological functions of the river,is an urgent scientific problem and research hotspot.Aiming at the realistic problem that river ecological base flow and regional ecological security are difficult to guarantee in the context of urban construction development,this paper studied the impacts of urban construction on the most withered monthly average flow and ecological base flow guarantee from the aspects of land area and water pollution and so on.The impacts were studied by using the methods of investigation and monitoring,sampling and analysis and model construction to simulate by taking Weihe River,Chashuihe River and the Xiaoweihe River around the Yangling Demonstration Zone as objects.The main results are as follows:1.The relationship between the area of urban construction land and the most withered monthly average flow of the Xiaowei River was quantified in Yangling Demonstration Zone.The cological base flow of Weihe River,Qishui River and the Xiaowei River around the Yangling Demonstration Zone were calculated.The recommended values of 6.0,0.2and 0.1 m3·s-11 were given by the most withered monthly average flow method,which can be used as the basis for the allocation of water resources downstream.There is a significant negative correlation between the area of urban construction land and the most withered monthly average flow of the Xiaowei River in Yangling Demonstration Zone,which is in line with the exponential function relationship.Under relatively stable climatic conditions,when the area of urban construction land in Yangling Demonstration Zone reaches 56.27km2 planned in 2035,the most withered monthly average flow of the Xiaowei River will be close to 0.1m3·s-1,and the problem of ecological base flow protection will have become very serious.When the area of urban construction land in Yangling Demonstration Zone is larger than 60 km2,the most withered monthly average flow of the Xiaowei River will be less than the ecological base flow of the Xiaowei River,that is to say,the ecological base flow will not be guaranteed without protective measures.Determining the relationship between the area of urban construction land and the ecological base flow of rivers at different levels can allocate water resources more reasonably with protecting river ecosystem,and further play a supporting role in planning ecological water use and promoting water system balance in the Weihe River Basin.2.A new method for calculating ecological base discharge from dominant discharge of rivers is presented in this paper.Based on the analysis of the internal relationship between the concept of ecological base flow and dominant discharge,we found the power function relationship between them by collecting the data in different rivers and proposed a new method for calculating ecological base flow from dominant discharge of rivers.The method was applied to the Xiaowei River and the verified results are within the error tolerance.Compared with the traditional method,this method has the advantages of simple calculation process and accurate calculation results,and is especially suitable for small rivers with less hydrological data in long time series and poor cross-section representation.The ecological base flow of rills,shallow ditches,cutting ditches and gullies are 3.67×10-5,0.02,0.21 and 0.4214.21 m3·s-1,respectively,calculated by this method from the source of rivers.Gully ecological base flow is the flow of guaranteeing the spatial ecological function of gully on the premise of avoiding soil erosion caused by further development.The calculation and analysis of the gully ecological basic flow is of great significance for guaranteeing the overall ecological basic flow of rivers from the source of rivers and opening up new ideas for the control and development of gullys.3.The impact of water pollution on the protection of river ecological base flow was clarified.The average concentrations of total nitrogen,total phosphorus,ammonia nitrogen and chemical oxygen demand in the Linghou section of the Xiaowei River around the Yangling Demonstration Zone are 14.37,0.31,1.28 and 39.5 mg·L-1through monitoring.According to the“National Surface Water Environmental Quality Standards”,the river nitrogen pollution is serious and the overall water quality belongs to the inferior V-type.The average concentration of pollutants in the Linghou section of the Xiaowei River in four seasons is obviously different,which is in line with the fact that the concentration in winter and spring is larger than that in summer and autumn.The average concentrations of total nitrogen and total phosphorus in the Gaogan canal water in Yangling Demonstration Zone are 14.51 and 0.70 mg·L-1,which also exceed the requirements of V-type water quality standards.The average concentrations gradually increased from upstream to downstream,and basically meet the exponential function relationship.Urban construction has a greater impact on phosphorus pollution.Poor water quality not only indirectly increased the water consumption of other aspects of ecological water demand,but also limited the use of high water quality water demand of rivers.More water is needed to maintain the health of rivers from the aspects of pollutant transport and water self-purification,which maked it more difficult to guarantee the ecological base flow of the Xiaowei River.4.This paper simulated the impact of urban construction on the ecological base flow of Xiaowei River.The SWAT model of Xiaowei River watershed was established and preliminary validated,which showed that the SWAT model can simulate the annual and monthly runoff of Xiaowei River watershed.When the urban construction land in Yangling Demonstration Zone was at the level of land use in 2015?33km2?,the monthly simulation flow guaranteed 70%to 0.1m3·s-11 or less than 50%to 0.33m3·s-11 of the ecological base flow of the Xiaowei River.The impacts of urban construction land on ecological base flow are as follows:dry season?Dec.Mar.?>normal season?Apr.Jun.And Nov.?>flood season?Jul.Oct.?.With the increase of urban construction land area,the difficulty of ecological water using will become more and more serious in dry season.The above results have laid a foundation for the further study of the impact of urban construction on the ecological basic flow protection and the improvement of the concept and method of ecological basic flow,which can play a supporting role in the development of ecological construction and the protection of river ecosystem. |
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