Research On The Flood Characteristics And Trends Of The Taohe Main Stream

The Taohe River basin, which is located in Gansu province, Northwest China, is facing serve arid and flood problem nowadays owing to the globe change as well as the activity of human beings. Thus, it is very essential to study the flood characteristics and trends of the Taohe River basin, which would provide valuable guidance for regional governments to prevent the disaster causing by arid or flood and support more rational use and management of the region’s water resources. We collected the measured annual maximum peak flow data from four representative hydrological stations from the upper, middle and lower reaches of the main stream of the Taohe River basin. First, the consistency of these data was examined by the hypothesis testing method. Secondly, we used the correlation method to extend the data series of the Chin groove stations, Minxian stations and Red flag stations, which measured data series did not extent to the year of1947, and making the data series of the four stations reunification from1947to2010, a total of64years. Then, used the method, such as Mann-Kendall rank correlation test method, moving average method, The linear trend regression analysis and maximum entropy method, we analyzed and calculated the changing characteristics, the trends and the cyclical nature for the maximum peak flow of the four stations; Finally, the relationship between the drainage area and index n was calculated and analyzed using empirical formula(Area analogy method).The maximum peak flow data series for the four stations was calculated and analyzed using traditional mathematical statistics. Viewed from the time, before the prior of1960s, the annual maximum peak flow values and the fluctuations of its series were both larger; From a spacial perspective, the inter-annual variability changes greatest change in upstream of the Taohe main channel, and it was changed minimum at Minxian station in midstream. The relationship between the mean annual maximum peak flow in Taohe River main stream and the catchment area was Basically as a straight line in the double logarithmic grid paper, but the point of Minxian in the middle reaches is above the fitted line.The changes characteristics and trends of the annual maximum peak flow data series of the Chin groove stations, Minxian stations, Li-jiacun stations and Red flag stations in the Taohe River basin mainstream are generally similar, although it was tested by different method, such as the Mann-Kendall rank correlation test method, the moving average method, the linear trend regression analysis and the maximum entropy method. Those results showed that all the method are accurate and effective, and give the following conclusions. From the Period of late1950s to the mid1960s, the annual maximum peak flow values of the Taohe River main stream showed an upward trend, but did not pass the test of significance, that meaning the upward trend is not obvious; and since the Period of1980s, it decreased gradually. Overall, the fluctuation of peak flow changes in a cycle of about25years. From the calculation of maximum entropy method, the annual maximum peak data series of the four station in Taohe River main stream also has a long cycle of about11years and22years, which would be accompanied to the fluctuations cycle of sunspot.From analyzing relationship between index n and the catchment area, we conclude that the Taohe River’s annual maximum flood peak almost appear in late August to early September from the selected typical flood hydrograph. Compared with the analysis based on the measured peak flow, it is more stable of the relationship between index n and the catchment area ratio with the analysis based on the peak flow of unified frequency. There is a decreasing function of linear relationship between the catchment area ratio and index n in each selected flood based on the measured peak flow. But for the analysis based on the peak flow of unified frequency, an increasing function of linear relationship is between the catchment area ratio and index n. The study found that index n is not only related to the catchment area, the flood hydrograph linear, but also related to the flood frequency and other factors.