Influence Of Precipitation Changes And Human Activities On Runoff And Sediment Characteristics In The Upstream Of Beiluo River

In this paper, the record, till the year2006, of monthly precipitation, runoff and sedimentdischarge at Liujiahe, Wuqi and Zhidan hydrological station in the upstream of Beiluo Riverwas selected to make a research on the variation of the corresponding period of annualprecipitation, runoff and sediment discharge and its annual and inter-annual variation. Withthe trend analysis using theMann Kendallrank correlation test method, the mutationanalysis using the sequential cluster method and theMann Kendallnon-parametric testmethod and the cycle analysis using the wavelet method and wavelet variance, the evolutiontrend of precipitation, runoff, sediment discharge and the relationships of water and sand inthe upstream of Beiluo River during the past50years was analyzed. And its responsemechanism to soil and water conservation measures and ecological environment constructionin the late1990s was discussed. It is expected to provide a scientific basis for watershedmanagement, soil and water conservation planning and ecological environment construction.The main results are outlined as follows:1.The research on the annual distribution process and non-uniform coefficient,thecentralization and variation of precipitation, runoff and sediment in the aera of Beiluo Riverupstream suggested that they mainly concentrated in the flood season at Liujiahe, Wuqi,Zhidan Station(from June to September),especially in July and August. As for the spacedistribution, the rainfall had no major changes, but the runoff and sediment increased fromupstream to downstream as the influence of the basin area and human activities. The sedimentloss often concentrated in several large flood. Since1970,the runoff and sediment in theupstream area of Beiluo River have significantly reduced. There may be a variety of reasons,of which the changes of rainfall and its underlying surface are inseparable.2. A linear regression equation of the annual precipitation, runoff and sediment dischargeto the time sequence was established. The trend of regression line showed that rainfall, runoffand sediment discharge declined with time. Further more, the decreasing tendency is checkedby use ofMann Kendallrank correlation test method for rainfall, runoff and sediment atthese three stations. Test results suggested that the sediment decreasing trend had the mostobvious significance, followed by runoff decreasing trend and the precipitation had the least significance. This showed that human activities had the greatest influence on the reduction ofwater and sediment in Beiluo River upstream except for the precipitation.3. The mutation point of annual precipitation, runoff and sediment discharge timesequence was preliminary analyzed by use of the sequential cluster method and itssignificance test was conducted by use of Mann-Kendall non-parametric test method and DPSanalysis software. The analysis showed that the mutation year of precipitation at three stationswas in the year1979.The mutation point of annual runoff at Liujiahe Station was in the year1984, the mutation point of sediment load was in the year1977and2001. At Zhidan Station,the mutation point of annual runoff was in the year1979and sediment load was in the year1996. At Wuqi Station, the mutation point of annual runoff was in the year1979and sedimentload was in the year1977. The mutation point of precipitation and runoff were close in time,but the mutation point of precipitation and sediment had quite a difference.4. With the application of DPS analysis software, the wavelet function and the waveletvariance, the temporal structure and periodic variation patterns of rainfall, runfall andsediment in the Beiluo River upstream region were studied. The results showed that there wasa periodic variation of annual runoff and sediment at Liujiahe Station, which had2years mainperiod and26years hypo-period. At Liujiahe Station, the main period was26years and itssubperiod was2years. The annual runoff and sediment of Zhidan Station had2years mainperiod and26years,8years hypo-period. The periodic variation of runoff and sediment atthree stations were in the same and runoff was the main reason for the periodic variation ofsediment.5. Taking the record of precipitation, runoff and sediment in the year1979, the mutationyear of precipitation at three stations, as the reference period, the linear relationship ofprecipitation–runoff and precipitation-sediment in the reference period was established byuse of the regression analysis. Then the influence degree and proportion of precipitation andhuman activities on river runoff could be separated. The changes of runoff and sediment withthe influence of precipitation and human activities for three periods were calculated and thereasons of these changes during different period were analyzed. Results showed that in the1980s, the influence of precipitation on runoff at Liujiahe, Wuqi and Zhidan Station was87.6%,42.1%and65.7%. The precipitation had a greater influence on runoff than humanactivities. The influence of human activities on sediment was72.81%,79.5%,72.1%,whichwas bigger than precipitation. Precipitation changes were the mainly reasons for the runoffreduction in the1980s. In the1990s, as the localized heavy rainfall in1994, which had someinfluence on runoff and sediment, precipitation and human activities had significant impactson runoff and sediment. During the first six years of the21st century, the influence of human activities on runoff at Liujiahe, Wuqi, Zhidan Station was69.7%,58.9%,72.9%, which wasbigger than precipitation. The influence of human activities on sediment was80.53%,92.14%,88.37%. Human activities become the main reasons for the reduction of runoff andsediment. According to the influence of precipitation changes and human activities on runoffand sediment in three period (the1980s,1990s and first six years of21st century) and thegreater influence of human activities on runoff and sediment in the first six years of21stcentury, conclusion can be made that returning farmland to forests, soil and waterconservation and the implementation of integrated watershed management is the fundamentalreason for the substantial reduction of sediment load.