Abstract:

The variation law of runoff has gained increasing attentions in hydrology and water resource research over the past decades,and is the key issue for sustainable use of regional water resources and water conservancy project.Exploration of the variation law of the flood seasons runoff in Zishui River Basin will provide an important theoretical reference in understanding the hydrological characteristics of the Zishui River and the sustainable use of regional water resources.River runoff changes also have some influence to flood and drought disasters of the river basin.Especially the frequency of flood and drought disasters in the southern,which occur in the flood season,is higher.As a typical representative of the southern river,Zishui,in recent years,shows an upward trend of flooding which brings great losses.Studying the variation law of the flood seasons runoff in Zishui River Basin also can provide a scientific basis for preventing flood and drought disasters.Based on monthly runoff data from 1990 to 2013 in the flood season of three representative stations in Zishui River Basin,including Luojiamiao,Lengshuijiang and Taojiang hydrological station,the intraannual changes of runoff in the flood season were analyzed by using nonuniformity coefficient and amplitude of variation; then application of these index values and flood and drought disasters in Hunan province has carried on grey correlation degree analysis; besides,the interannual changes of runoff in the flood season were studied by moving average and the MannKendall mutation test.The results are as follows. (1) During the flood season,the distribution of runoff was quite uneven in the Zishui River Basin,however,the runoff distribution tended to be even with the lapse of time.The monthly runoff showed a decreasing trend with fluctuation.As a whole,the indicators from the three stations presented a decreasing trend.(2) The grey correlation degree of runoff distribution characteristic index value during the flood season and river basins flood and drought disasters was extremely high.The characteristics of annual runoff distribution in the flood season of Zishui River Basin could better reflect the current years flood and drought disasters.The larger the value of the four indicators which reflect the uneven distribution during the flood season was,the more often flood and drought disasters would happen.(3) The distribution of interannual flood seasons runoff of Zishui River Basin was quite uneven,too.At first,it showed an increasing trend,then it fell,and it rose finally.However,in general,it presented a trend of decreasing.(4) Luojiamiao station,Lengshuijiang station and Taojiang station broke through the 95% confidence interval in 2007-2013,1990-1991 and 2010-2013,1990-1991 and 2004-2013,during these annual times the flood seasons runoff showed a trend of a significant reduction.Luojiamiao station and Lengshuijiang station appeared mutational sites in 2009 and 2010.For Taojiang station,UF statistics did not intersect with UB statistics and there have been no mutational site.