Influences Of Runoff And Sediment Of Wuding River Watershed By The Changing Environment

Watershed is a dynamic system to human activities and climate change with keenlysensitivity，and the most active part are water and sediment variation. Water and sedimentreduction, lagre interannual variations and interannual uneven distribution appears complexphenomena in Wuding river watershed, under the dual function of climate changes and humanactivities.Taking Wuding river watershed as the object, cognition is on water and sedimentevolution and its constraints, by studying water and sediment flux under the climate changeand human activities.It contributes to a better understanding of the structure and function ofthe watershed and water cycle of the watershed. The paper provides theoretical basis forWuding river basin water resources development and utilization and rational distribution.The tendency analysis, the periods and abrupt change were carrying on bymeteorological and hydrological sequence from1956to2004in the research area, withadopting various statistical methods.Combining datas of basin soil and water conservation andland-use datas in different periods, the paper analyzes the impact of human activity on waterand sand. Impacts of rainfall and the human activities on water and sediment were producingby quantitative estimation.Applications of ARIMA Model, BP Network Model and graytopology forecast method were used for water and sediment forecast.Based on the aboveanalysis, the following main conclusions are obtained:(1) Change characteristics of microclimatic factors in Wuding river watershedInterannual variability processes of annual average precipation, annual averagetemperature, evapotranspiration arid index and humid index were analyzed, by yearly average,linear regression and five-year moving average methods. The article introduces the jumpchange of climatic factors with accumulative mean deviation curve anomaly curve, and thejump spot by slipping rank sum method, slipping run-length, R/S mutation method andordered cluster analysis. Wavelet transform and maximum entropy spectrum were applied forthe climatic factors periodic analysis in the Wuding river watershed. As it turned out: Average annual precipitation and evaporation show a declining trend, and the annual averagetemperature increased obviously in49years; basin precipitation fluctuations are large withcoefficients of variation(CV) being0.34; annual mean temperature variation rate reaches0.29℃/l0a, and annual average temperature reflected an increase very significantly; theevaporation reduce reaches about702mm;drought index and humid index fluctuate around themean value and the change is not significant.Viewing from the point of variation within a year, Wuding river basin shows the floodseason, non flood season and seasonal typical feature. Rainfall distribution greatly influenceon basin rainfall characteristics in summer, autumn and the flood season.Average temperatureis a typical curve with single peak shape, and annual temperature exhibits large variances.Peak was found intensively from June to August. Evaporation distribution is uni-modal curvein all months, with peak concentration in May-July.The flood season evaporation accountedabove70%of the total evaporation.(2)Runoff and sediment temporal variation characteristics in Wuding river watershedTo explore the change process of water and sediment in the Wuding River basin, waterand sediment interannual changes displayed the same trending.The calculation results indicatethat water and sediment all demonstrated a oscillating and declining trend. Sedimentdecreased more significantly than runoff, both are concentrated in July-September.Characteristics of water and sediment time series are on agreement with the precipitationseries.Water and sediment has mutation for1971year, and they exist obvious periodicaltransformation rules and the results were closed. Annual runoff exists28a,20～22a,10～13aand5a periods, and the main first cycle is22a. Annual sediment exists21～24a,13a,5～10aperiod, and the main first cycle is13a. Sediment was obviously positively correlated withrunoff. Regression coefficient of relationship between water and sediment was0.6657.(3)Water and soil conservation measures and land use effect on water and sedimentFrom the aspects of temporal and spatial variation, land-use degree changes, land-use typetransfer, the watershed land-use evolvement was analyzed,which was based on1985,1996and2000year land use data.Different land use types display frequent circulation, fromtransition matrix of land use, and the main types of land use conversion were conversion fromother land-use types to grassland and farmland. Unused land conversion was the most activeland-use type during1985-1996. However, the most active transforming land use type waswoodland from1996to2000. In different periods, land use change on the reduction of waterand sediment contribution rate was more than50%. According above description, land usechange is an important cause of the water and sediment reduction.Comprehensive control of soil erosion is one of main reasons that cause the reduction ofwater and sediment. Increment of the soil and water conservation area was in the positive correlation with water and sediment reduction, meanwhile they obtained satisfactorycorrelation. Growth rate of annual sediment reduction by soil and water conservationmeasures is less than the impact of reduction on runoff. Forest-grass measures for soil andwater conservation and benefits of runoff and sediment reduction were higher degree ofcorrelation. Forest coverage rate increased with the increase of soil and water conservation,and the weakening effect is illustrated for the control measures of soil and water loss on thewater and sediment dynamics.(4)Flow and sediment evolution and response of the changing environment in Wuding riverwatershedCorrelation is analyzed between temperature, precipitation and water and sediment.Results show that correlation of precipitation and water and sand was stronger thantemperature. Coefficients of correlation between annual precipitation and water and sedimentrespectively were0.73and0.52. The response of water and sediment variation on climaticfactors is mainly for the effect of rainfall.The effects of climatic variations and human activities on water and sand were assessedthrough the double cumulative curve and linear regression method. Results indicate thathuman activity is a major factor affecting water and sediment changes of the Wuding riverbasin which influence on runoff and sediment respectively were72.06%、57.8%. Impactlevels of human activities on runoff reduction of Wuding river watershed reach the maximumin the90’s of20Century, however after entering the21century, the level decreased. With thepassage of time, influence degree on human activities lightened. While influence degree ofclimate change on sediment gradually strengthened, nineteen nineties reached the minimum,and influence degree with the abrupt increasing after twenty-first century.(5)Water and sediment predictionBased on Matlab neural network toolbox, the paper sets classic3-layer BP neuralnetwork prediction model for water and sand of the Wuding river basin. Using differenceauto-regressive moving average model(ARIMA) to predict runoff and sediment of floodseason and non-flood season and water and sediment were simulated with GM (1,1) graytopological predicting model.The precision of three models for runoff forecasting meets therequirements of short-term prediction. For simulation on sediment sequences, the precision ofBP network and gray topological were higher than ARIMA model, and the results were joinedbetter fitting better.