| Abstract:The change of river sediment is the results that change of regional ecosystem environment. It will directly cause the scour and silting evolution of river channel, which seriously affect the engineering, wetland, environment, biodiversity, etc. There are many high sediment concentration rivers in China, and the sediment problem is very serious. Water and sediment disasters seriously restrict the sustainable, rapid development of the national economy. So further understanding of the sediment has become a very urgent task of hydrological research. This paper takes Panlonghe basin, the branch of Red river as the studied area, the wavelet, chaos, fractal, neural network, "3S" technology and various traditional mathematics methods as the study methods, to research the change regulation of sediment flux in Longtanzhai gauging station. Moreover, this paper also has researched the mutual influence and response among climate, human activity and sediment. At the last, we come to the conclusions as following:1. The results of time series analysis showing that the suspended sediment flux of Panlonghe had been present a trend of waving ascension from 1953 to 1997 year. However, it had been present a trend of descendent tendency from 1998. The change of suspended sediment flux has multi-time scale characteristic, and the oscillation strength is different in different time period. To the periodic characteristic, the suspended sediment flux has the oscillation period of 4,7 and 22 year, in which the oscillation period in 22 year time scale is the most obvious, it run throughout the whole researched time. However, the local characteristic is outstanding both in 4 and 7 year time scale. If we analyze the abrupt characteristic in the 4,7 and 22 year time scale, we can come to the conclusion that in the 4 year time scale, abrupt change has 27 times, and in the 7 year time scale, abrupt change has 15 times, and in the 22 year time scale, abrupt change has 5 times. The long term time scale contains the short term time scale. In additional, the multi-time scales, periodic and abrupt change characteristic are controlled by the climate factors. 2. The results of nonlinear features analysis showing that the transportation processes of suspended sediment have the two kinds of nonlinear characteristics, that is, chaos and fractal. Firstly, from the aspects of chaos characteristic, to the mean month suspended sediment flux of Longtanzhai gauging station of Panlonghe river, the minimum embedding dimension m=11, saturation correlation dimension D2=1.8387, maximum Lyapunov exponent?1=0.108, Kolmogorov entropy K=0.1818, which mean that the maximum possible forecast time is about 9 months, and the mean possible forecast time is about 6 months. Secondly, from the analysis results of fractal, to the mean month suspended sediment of Panlonghe river, the Hurst exponent H=0.7781>0.5, fractal dimension D=1.2219.3. When analysis the relationship between river suspended sediment transportation and land use change in Panlonghe basin, we can come to the conclusions that the change trend characteristics of suspended sediment flux in Panlonghe basin is the results of land use change, and in particularly the changing of forest area. This was mainly due to land use and soil erosion have closely relationship, and the land use mode change will lead to soil erosion intensity change, thus leading to erosion and sediment transportation make corresponding adjustment.4. This paper uses the Wavelet Network in the process of suspended sediment prediction. Firstly, in the model of sediment-climate, the input factors include four climate factors and only one hydrological factor. That is, rainfall, air temperature, the accumulative amount of daily rainfall?25 and?50 mm, and water discharge. After this step, we divided the models into four groups according to the different combination. The first group only includes rainfall and air temperature; the second group adds downfall and rainstorm except the two factors that the first group used; the third group adds the water discharge except the factors that the third group used; the fourth group only includes the water discharge. When come to the delay effect, we consider four conditions, that is, have no delay effect, one month delay, two and three months delay and four months delay respectively. The results are as following:if add the water discharge and consider the influence of downfall and rainstorm, the prediction precision will be improved; the best delay time is one month, the prediction precision will reduce if the models have no time delay or time delay excesses two months; the prediction precision of the Wavelet Network is better than the Back Propagation model. Secondly, in the model of suspended sediment and human activities, the input factors include nine factors, that is, woodland area, farmland area, capability and controlled area of reservoir, length of highway construction, the water and soil conservation area, year mining amount, bare land area and the total population in the studied area. The results are as following:add the on time and delay one year of woodland and reservoir controlled area to the sediment-climate models can improve the prediction precision. However, if add the farmland area, reservoir controlled area, length of highway construction, the water and soil conservation area, bare land area, year mining amount and the total population in the studied area to the model, the prediction precision improved slightly. It is clear that these factors influence the production and transportation of suspended sediment, but their effects are limited in the studied area.5. The result of the influence of climate change to the suspended sediment flux showing that the influence of climate to the change of suspended sediment flux is different in the different period. In generally speaking, the contribution rate of climate change to the change of suspended sediment flux is weakening.In this paper, we mainly consider the rainfall, temperature, downfall and rainstorm when study the influence of climate factors to sediment. The results are as following:comparing to the standard period, the contribution rate of rainfall to suspended sediment change is the most important, all excess 85%; the contribution of temperature to the suspended sediment flux change is counteractive, and less than 3%; downfall and rainstorm have certain influence to sediment, but the contribution rate are less than 6%.After analyzing the response of sediment transportation to the climate change, we can come to some interesting conclusions. For the climate factors:the air temperature rising will lead to the sediment transportation decrease if the rainfall is not change; if the air temperature is not change, the influence of increase rain to sediment transportation is more observably when the rainfall have same decrease and increase range; if the air temperature rising with the rainfall decrease, the sediment transportation will decrease; if the air temperature rising with rainfall decrease, the sediment transportation change is more complicated. The sediment transportation will become more sensitive to the same climate change scenario under the scenario of human activity intensified.6. The results of the influence of human activities to the suspended sediment flux showing that the influence of human to the change of suspended sediment flux is different in the different period too. In generally speaking, with the development of society, the control of human to the sediment is intensified.From the results we know that:the contribution of woodland to the sediment transportation is the most important factor, it contribution all excess 70% in the four periods, so it is clear that the sediment transportation rising is caused by the woodland decrease; for the farmland, from 1958 to 2005 year, it has been presented decrease trend, so its contribution to sediment transportation decrease was increase; for the reservoir controlled area and capability, because almost all of the reservoir were built at 50 and 60's, so their effect of decrease sediment transportation were presented in the fore period, after 2000 its decrease sediment effect was very limited; for the road construction and mining, in the early period of the studied stage, their contribution to the sediment increase were very limited, but their contribution to the increase of sediment are can not be ignored since 1990s; for the water and soil conservation, it developed very slowly, and its contribution reaches to 5.64% since 2000s; for the bare land, its contribution to the sediment increase was 4.23% in the early period, and reached 11.26% in 90's, but decreased towards 10.57% when we got into 21st centuries; for the year-end total population, it does not contribute to the sediment transportation directly, but it influence sediment transportation through the other factors, and its contribution is about 4%.After analyzing the response of sediment transportation to the human activities change we can come to the conclusions as following:when the farmland area doses not change, the decrease of woodland area will cause the sediment transportation increase, but the sediment will decrease if the woodland area decreases; when the woodland area doses not change, the decrease of farmland will cause the sediment transportation decrease, but the increase of farmland will cause the sediment transportation increase; woodland area increase with the farmland decrease, the sediment transportation will decrease; woodland area decrease with the farmland area increase, the sediment transportation will increase. So when we analyze the response of sediment transportation to both of the farmland and woodland area change, we need to analyze the special conditions based on the given environment. For the response of sediment transportation to the human activity under the climate change, the sediment transportation is not so sensitive when the climate becomes wetness.7. For the possible change of sediment under the future climate in the studied area, if take the sediment transportation of 2000?2005 years as the reference, the possible change range of sediment transportation is 0.15?16.8%. However, if take the human controlling abilities are improved into the consideration, the total direction of sediment transportation may tend to decrease, which is alike many basins in the world.In a word, the above mentioned results infused new scientific theories and mathematics method into the research of sediment in the basin, and developed new research direction. Not only they advanced the people's cognition and comprehension to the sediment transportation process, but also provided a theories basis for the establishment strategy to the sediment controlling in the basin, which have useful meaning. |
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