Analysis On Trend And Driving Factors Of Base Flow In Kuye Catchment

The variation of base flow is a comprehensive reflection of the change of regionalclimate and human activities, and it is an important element to maintain sustainabledevelopment of the ecosystem. In this study, the Kuye catchment, a tributary of the YellowRiver, with a drainage area of8706km2on the Loess Plateau, was chosen to investigate thechange trends and evolution characteristics of base flow. Based on Chapman-Maxwell baseflow separation technique, the total runoff from Wenjiachuan hydrological station, which isthe maximum control station in the Kuye catchment, was separated into surface runoff andbase flow. The evolution of rivers base flow driving factors were analyzed from climatechange to human activities. It could be useful to understand and evaluate the function ofsoil conservation measure that have been implemented, and guide the future constructionof ecological restoration in this catchment. The results of the analysis in the thesis are asfollows.1. Eight kinds of base flow separation methods were used in the Kuye catchment. Theresults showed that Chapman-Maxwell filtering method and Eckhardt filtering methodseparated most objective and stable base flow, which can be used as optimal base flowseparation method in this study area.2. It showed that the average annual base flow was24.72mm, accounted for38%oftotal runoff. For the temperature rising in early spring and monsoon rainfall, thedistribution pattern showed two peaks in March and August among months, which occupied13.94%and20.20%of total average annual base flow, respectively. The baseflow in summer was rich and base flow in winter was least. The base flow in wet seasonwas1.4times than dry season.3. In the past50years, a significant negative trend was detected in the annual baseflow in all7time periods. For total year period, the average change rate was0.628mm/a.The change points significantly occurred in1980and1996. Analysis of flow durationcurves showed that, compared to the contrast period, the relative changes of annual baseflow for5%,50%and95%exceeding time were greatly reduced in the treat period and thecoal mining period.4. It used fractal dimension of the fractal theory and shape factor to express themorphological characteristics of different components of runoff daily process line. Forfractal dimensions of runoff daily process line, surface runoff was biggest with a value of1.0986, total runoff was second with a value of1.0927, and base flow was smallest with avalue of1.0288. For shape factors of runoff daily process line, total runoff was biggestwith a value of16.7964, surface runoff was second with a value of14.8280, and base flowwas smallest with a value of4.8907. It was obvious that the morphological characteristicsof runoff daily process lines were vary from each other. For surface runoff, it showed thatprocess line was most complex fluctuation change with an advance peak and high thinpeak type; For total runoff, it showed that process line was complex fluctuation changewith an advance peak and high thin peak type; For base flow, it showed that process linewas most gently fluctuation change with a lag peak and squat peak type. Compared to thecontrast period, the characteristics of the fluctuation complexity and local peak of therunoff process line in the total runoff, surface runoff and base flow revealed smaller in thetreat period and the coal mining period.5. The significant negative trend in base flow was a comprehensive effect of thechange of regional climate and human activities. It revealed that the change of precipitationwas a reason for negative trend of base flow, but potential evapotranspiration had littleimpact base flow in the Kuye catchment. Analysis of the factors of human activitiesshowed that the main factor for base flow trend was that excessive exploitation of a largearea of coal resources, utilization of groundwater and building of hydraulic engineering. Itplayed a positive effect on base flow by soil conservation measures that increased rainfall infiltration. However, the trend of base flow was a comprehensive effect of the change ofregional climate and human activities.