The Period And Trend Analysis Of Streamfall And Sediment Load In Yan River Based On Time Series

Yan River in the middle reaches of the Yellow River has become the most serious soil erosion situation in one region. The climate, geography and the valley over the past 30 years the impact of human activities, resulting in the Yanhe River Hydrological complex phenomenon. In this paper, the trend, singularity, period and random was study by the precipitation, streamfall and sediment transport measured data in Yan River basin from 1950s to 2000. In order to understand and grasp the comprehensive management of soil erosion on the Loess Plateau ,and provide a scientific basis for the regional process of quantitative evaluation of soil erosion and modeling. The results of the analysis in the paper are as follows.1. On the 8 level of Wavelet transform, since the 1950s, the precipication and the sediment transport series showed a downward trend, the streamfall series singularity existed in 1979, from the 1950s to the late 1970's upward trend, the 1980s has been a declining trend. On the 7 level of Wavelet transform, since the 1950s, the precipication series singularity existed in 1966,1988, the streamfall series singularity existed in 1965,1978,1988, the sediment transport series singularity existed in 1965,1977,1987. The hydrological time series was divided into some sub-series by those singularity, the trend variance of sub-series are consistent, but there are significant differences.2. Since the late 1950s, the trend correlation coefficient of precipitation and sediment transport is better, but the correlation coefficient of precipitation and streamfall, streamfall and sediment transport is relatively poor. If the limits in 1979, the hydrological time series of Yan River basin will be divided into 1957 to 1978 and 1979 to 2000. Mann-Kendall method indicates that the early trend correlation coefficient of precipication and streamfall is high than the latter part. In the latter part, human activities intensified soil erosion, the relationship of precipitation and streamfall was desturcted. The latter part of trend correlation coefficient of precipication and streamfall is high than the early part. May be related to the devellpment of human unreasonable use of water resources in latter part, the hunman activities undermined the sediment surface, increased production volume of water and sand , result in precipication and sediment transport has more relevant.3. The precipitation, streamfall and sediment transport of the Yan Riverhad significant periods and their sizes were approximate. They were 3,6.5,13 and 23 years. The main period for precipitation was 3 years and for both streamfall and sediment transport, it was 23 years. On the micro scale corresponding to the period of 3 years, the annual distribution of precipitation after 1970's became uniform over the time. The three curves of the precipitation, streamfall and sediment transport became turbulent from 1970's to the beginning of the 1980's probably due to the soil and water conservation measures increased dramatically in the period. The three curves returned consistent probably due to the damage and weakening of the conservation measures after 1980's. For both the middle scale with 13 years and the macro scale with 23years, the curves of streamfall and sediment transport turned out to be out phase, or lagged the precipitation curve in some periods. Their periodicity showed that precipitation was the main outer deriving factor for Yan River producing streamfall and sediment, however the human activities were the another important factor to influence their period changing.4. Combining Wavelet transform with ARIMA model to forecast the monthly streamfall of Yan River basin in 2000, the results showed that a relatively good accuracy compare to the using directly ARIMA model. The average relative error from 34.8% to 27.8%, the consistency indicators from 0.70 to 0.68, the coefficient of effective from 0.80 to 0.85.5. This paper was first introduced that Combining Mann-Kendall method with the Wavelet transform for the analysis of trends and effectively test the singularity of hydrological time series, and quantitative analysis of trends in composition, improve the scientific analysis of the trend. Based on the multi-bands wavelet, the period of the precipitation, streamfall and sediment transport was analyzed on the same scale. A new way was proposed for the relationship of climate and hydrological process and human factors, and the process of periodic changes in Yan River basin.Elements of the hydrological changes in the law is a complex hydrological phenomena. Wavelet transform as a new methods is immature, the results of this paper are still to be discussed. Different scales on the linkages between hydrological elements are difficulty for analysis of the hydrological scale effects.