The Impact Of Baseflow On Ecological Water Requirement In The Huaihe River Basin

Baseflow is an important component of streamflow.It not only plays an important role in streamflow formation,maintain and the process of renewable,but also has the extremely important role and significance for the guarantee of ecological water requirement(EWR)and the health of river ecosystem.In recent years,baseflow showed a downward trend because of the impact of human activities and natural factors.This would mean that the support ability of groundwater on streamflow is abated,and then lead to streamflow reducing,the guarantee of EWR declining,even rivers drying up.As the problem of global water resources increasingly prominent,baseflow separation and EWR become research focuses in the Ecohydrology.At present,many scholars at home and abroad have been carried out a large amount of research,but less attention to the impact of baseflow on EWR.The research for the influence of baseflow on EWR is useful for in-depth understanding of the regional water cycle and water balance,optimization of water resources allocation,maintain ecological function and so on.Therefore,this paper chooses Huaihe River Basin(HRB)as the study area,analyzed the impact of baseflow on ERW.The major results in this paper are summarized as follows:(1)On the calculation and rapid assessment methods of EWR.Based on the change characteristics of natural runoff and eco-hydrological processes on runoff dynamic demand,this paper puts forward a new calculation method of EWR,called the dynamic calculation method of EWR.This method determines and computes percent of the average flow in the same periods based on the feature variables of natural runoff process,avoiding the shortage that traditional hydrological method putted the specific percentage of average annual runoff or specific guarantee rate of frequency curve of natural runoff as hydrological index to calculate EWR.So,this method has better regional representative and universal applicability.2)Satisfactory degree of EWR is one of the important indicators in river health.Therefor,based on the Cluster analysis,Mann-Kendall test and the function of spatial analysis of GIS,a new method for fast evaluating satisfactory degree of EWR is proposed.The method can identify the regions which are seriously lack of EWR and assess the effect of EWR allocation in a river basin.The satisfactory degree of EWR in river basin is defined as the degree of the difference between the real EWR use and the natural water consumption.(2)The spatio-temporal variability of baseflow and its contribution to streamflow in the HRB.Based on data collection and method optimization,digital filtering method has been employed to ealculate baseflow in the HRB,and a omprehensive analysis was made on the spatio-temporal variability of baseflow and its contribution to streamflow.The results show that:1)the HRB can be divided into five regions by baseflow modulus which is as the supply intensity of groundwater to surface water.Bseflow modulus in the north of the Huaihe River is lower than the southern region,and is presented decreasing trend from the upstream area to the midstream area.The nonuniformity of annual baseflow distribution in the Huaihe River System(HRS)is smaller than the Yishusi River System(YRS),and is presented increasing trend from the upstream to the midstream in the HRS.The maximum values of baseflow appear in August and September,and the minimum value in January～April.Both of them are generally presenting the trendency of delayed gradually from south to north across the basin.The trends of baseflow in the HRB have obvious spatial heterogeneity,even in the different sections of river showing the opposite trend.Mengcheng section and Linyi section showed a signifieant decreasing trend,while an significant increasing trend occurred in Mingguang section,and abrupt changes happened in 1973,1975 and 1971,respectively.2)The maximum contribution rate of baseflow on streamflow is bent on January,November and December in the HRB,and the value is more than 70%.Obviously,in these months baseflow is the major component of streamflow.On the other hand,the minimum contribution rate appears in July in the basin,generally less than 20%.So,in this month baseflow is not the major component of streamflow,but still an important part.On interannual contribution side,the maximum contribution rate is largest in dry years(75%or 95%),about 40%-60%.In summary,baseflow would be a more important source of streamflow in dry years,especially in dry seasons or months.(3)The contribution of baseflow on EWR in the HRB.The dynamic calculation method of EWR was used to calculate EWR in the HRB based on natural streamflow time series.Coupling previous calculation results of baseflow and EWR t,the contribution of baseflow on EWR is analyzed.The results show that:annual contribution of baseflow on EWR is relatively high.In wet year,median water year and dry year the EWR can be guaranteed by baseflow.While in particular dry year,some rivers(such as Honghe River,Yinghe River,Chihe River and Tuohe River)appear different degree of loss,but the contribution rates are still more than 50%.Thus it can be seen that baseflow plays an extremely important role in the maintenance of EWR in the HRB.The lowest contribution rate in the whole basin is occurred in April～June,even in Zhoukou and Mengcheng sections in the south of Wangbeng region,Mingguang section in the Benghong region,and Linyi and Daguanzhuang sections in the Yishuhe region,the contribution rate is only between 15%～40%.This phenomenon is more obvious in dry year and particular dry year.So,in dry year and particular dry year,especially in April～June,EWR can not be fully guaranteed by baseflow.(4)Evaluation and security research of EWR in the HRB.Extensive investigation was done on the spatio-temporal characteristics of measured streamflow in the HRB.Coupling the measured streamflow data and EWR,a rapid assessment method for the satisfactory degree of ecological water requirement(SDEWR)was carried out in the HRB.We found that:l)Except the headwater catchment of the basin with an insignificant increasing trend,the direction of annual streamflow trend was downward across the basin,especially in the YRS and the north of the Huaihe River being statistically significant.The most significant season of streamflow downtrend respectively appeared in spring and summer in the HRS and YRS,because the downtrend in April and May is the most widely and strongest in HRS,and July in the YRS.2)On the whole,SDEWR is higher in the upstream area than the midstream area,and is higher in the south than the north bounded by the Huaihe River.The trend direction of SDEWR was increasing in the upstream area,but shifted downward in the midstream area.The SDERW in April～June is the lowest,and has the largest spatial difference.So,it is recognized as the sensitive period of EWR in the HRB;The sensitivity areas are some sub-basins,including Wohe River,Chihe River and Tuohe River where EWR cannot be guaranteed at more than one-third of the time in a year.3)Comprehensive analysis of the contribution of baseflow on EWR and the spatio-temporal characteristics of SDEWR,combining the natural and social attributes in the HRB,study area can be divided into three types of reaches or regions:water resources development and utilization,Water conservation,aquatic ecosystem protection and rehabilitation.