Study On The Law Of Tuwei River Runoff Evolution Under A Changing Environment

Affected by environmental factors, the water cycle of Yellow River basin has atremendous change in the past50years, which mainly reflects in the decrease of the watervolume, uplifting river, water pollution, etc.Tuwei river basin is one of right bank branches inthe middle Yellow River (from Hekou to Longmen), and the famous coal chemical industrypark located in the central basin, which make the Tuwei river basin become an important partof China's energy and heavy chemical industry base of North Shaanxi area. In recent years,the large number of the soil and water conservation measures and implementation of theconstruction of water conservancy projects have changed the underlying surface conditionasfor surface and underground runoff generation, and have changed the distribution pattern ofwater resource and its utilization. So, study on the regional runoff features, evolution causeshas the great important significance for water conservancy project construction and waterresources development.In this thesis, taking Tuwei River basin as the research object, based the theory ofstochastic processes, Hilbert Huang transform theory, the theory of wavelet transform, andcombined with the traditional method of mathematical statistics, focus on runoff statisticalcharacteristics, trends and mutation characteristics, multiple time scale fluctuation, and theeffects of climate change and human activities on runoff change. Obtained the followingconclusions:1.The average annual runoff of Tuwei River is3.46×10~8m~3(from1956to2005), and thedistribution of runoff is non-uniform, from seventh month to eighth month is the main floodseason, maximum runoff occurred in August, and minimum runoff occurred in January.Before1970s, the average annual runoff is4.23～4.33×10~8m~3, after1970, the average annualrunoff declined rapidly, from the year of2000to2005, runoff was reduced to2.20×10~8m~3.2. Rainfall in Tuwei River Basin showed obvious dropping tendency between diffenertyears, and decline significantly, but the precipitation series have no significant mutations.Andthe annual runoff series also has a significant dropping tendency, and runoff sequence ofGaojiabao Station has a significant mutation, and the significant mutation of the year is1983.And also, the significant mutation of the year in Gaojiachuan station is1979.According to the different characteristics of the mutations between precipitation andrunoff and the different mutation point of upstream and downstream hydrological stations of runoff sequence: the main reason of runoff mutation in Tuwei River is human factors3. Through the EMD method, Runoff series in Tuwei River was separated into three IMFcomponents and a significant trend of decreasing component sequence, which have differentwave cycle. Make the significance test for each component to the original sequence and theresult is: In the3order components of the runoff series, the first and the second order IMFcomponent accord with significant test conditions, which means the first and the second orderIMF component contains the main information of original sequence and the correspondingperiod (3-4a,8-9a) can be used as the lord of the runoff series cycle.Make the correlation analysis between rainfall IMF components and runoff IMFcomponents, the results show that the correlation between rainfall and runoff is better in thesmall scale; the precipitation fluctuations in a small scale may lead to a corresponding changein runoff series.4. Using wavelet analysis method to analysis runoff and rainfall series fluctuationcharacteristics in different time scales in Tuwei River basin:Runoff series in Tuwei River basin have5years,13years, and38years cyclefluctuations, which control the runoff evolution characteristics in the whole time period.Between the1956-1975periods, annual runoff has severely oscillation in3～9a timescale, and has a high frequency fluctuation and a clear alternate change between the high-flowperiod and the low-flow period, which has the same characteristics in10～16a time scale andwave amplitude variation are relatively stable. In30～45a time scale, runoff series has twohigh-flow period (1963～1974a,1988～2000a) and one low-flow period (1975～2000a).5. Conclusion comes from Hilbert Huang transform and wavelet analysis to study runoffevolution is consistent in small scale, and the correlation between rainfall and runoff is betterin the small scal, the precipitation fluctuations in a small scale may lead to a runoff series hasa corresponding change, but human activities may lead to the large-scale fluctuations ofrunoff series.6. Under the influence of climate change and human activities, the annual runoff serieshas a significant dropping tendency. Suppose in1956-1978as the benchmark period, Set themultiple regression equation of the annual runoff and precipitation in benchmark period, andSeparate the amount of influence cause of the precipitation and human activities on the riversrunoff. And results found that the influence of human activities has become the main reasonfor runoff reducing in Tuwei River.