近60年赣江水沙变化特征及影响因素分析

CHANGING CHARACTERISTIC AND ITS IMPACT FACTOR ANALYSIS OF STREAMFLOW AND SEDIMENT OF GANJIANG RIVER BASIN DURING PAST 60YEARS

赣江是鄱阳湖流域最大水系,赣江水沙变化对鄱阳湖入湖径流、泥沙等水文特征有重要影响。目前对赣江水沙研究主要集中在下游外洲站河段,不足以反映全流域水沙变化规律。选取赣江上游4站、吉安和外洲水文站分别代表上、中、下游河段,基于近60a的实测流量、悬移质泥沙资料,采用水文学和数理统计相结合的方法,分析赣江水沙年际变化特征以及可能影响因素,以期为流域水沙资源管理提供参考。结果表明:(1)赣江径流年际变化大,1970s、1990s水量较丰,其它年代径流偏少,年径流序列无显著变化趋势和突变点;(2)输沙量年际变化剧烈,呈显著降低趋势,上游4站、吉安站、外洲站输沙序列突变点分别为2002年、1995年、1995年,突变后年输沙量较突变前减少52%、71%、67%;(3)赣江上游水土保持建设是上游4站输沙量减小的主要原因;1993年后万安水库拦沙是吉安、外洲站输沙量显著减少的主要原因,水土保持、河道采砂也是引起吉安、外洲站输沙量减少的直接因素。(4)水土保持减沙的作用是缓慢和滞后的,而万安水库对下游河道的减沙作用是迅速而显著的。可见,赣江入鄱阳湖的年径流无明显减少趋势,入湖输沙量显著减少,有利于减少鄱阳湖的泥沙淤积、促进湖泊生态的良性发展。

Ganjiang river is the largest river system of Poyang Lake Basin.The change of streamflow and sediment in Ganjiang river has an important influence on hydrological process of Poyang Lake.However,the current research on streamflow and sediment of Ganjiang river is mainly based on Waizhou hydrostation,the control station at downstream.That may leads to an incomplete understanding about hydrological characteristics of entire basin.This study systematically examined the changes of discharge and sediment load and their possible causes,which may provide reference for water and sediment resource management of river basin,according to the long-term measured data recent 60 years at six representative stations.Those stations are four stations（Hanlinqiao station,Bashang station,Julongtan station,Xiashan station）at upstream,Jian station at midstream and Waizhou station at downstream.The nonparametric Mann-Kendall test and moving t-test were applied to detect the change in annual streamflow and suspended-sediment.Results indicated that：（1）Great variability at annual and interannual scales on discharge was analyzed at upper four stations,Jian station and Waizhou,with variation coefficient as 0.31,0.29,0.28 respectively.1970sand 1990 swere regarded as abundant water time,as average runoff at major stations during those period were 103%-113% than average from 1953-2013,while the other were flat or low water years.No significant trends and abrupt points were detected on streamflow,and annual changes were more slightly obvious in upper stream than downstream.（2）In-phase relations between sediment load and streamflow were observed on shorter time scales before 1992,which may imply a considerable influence of the runoff on sediment transport.However,obvious different tendency were detected between streamflow and sediment during 1993-2013 owing to great reduction of sediment at all stations.Detailed examination shows annual sediment load change was more dramatic compared to runoff,with variation coefficient ranging from 0.46-0.62.An abrupt point of sediment at the upper four stations,Jian station and Waizhou station came out in 2002,1995 and 1995,with relative change rate at 52%,71%,67%respectively.（3）The flow duration curves and monthly average sediment concentration were analyzed to explore possible causes of sediment reduction.There were no significant changes on flow duration curves,while monthly average sediment concentration after abrupt points has decreased to 30%-49%,which acts as a major cause for the decreasing annual sediment.Both decreases in annual sediment and in sediment concentration at the upper stream can be linked with recent human activities,mainly including soil erosion control and reforestation.Although the upstream sediment decrease has certain influence on the downstream,reservoir construction,especially Wanan reservoir which capacity was 2.2billion cubic meters and operated from 1993,was a main cause of the decreasing trend of sediment at Jian and Waizhou station.The average annual deposition of suspended-sediment in Wanan reservoir was estimated to 400×104t.In addition,soil erosion control and large amounts of sand mining activities at downstream were contributed to the decreasing trend of sediment at Waizhou station.（4）The impact of soil and water conservation measures on reduce sediment was slow and hysteretic,while influences of sediment reduction of Wanan reservoir is prompt and significant.In concluded,a significant decreasing trend was observed on annual sediment load,while the runoff into the Poyang Lake from Ganjiang river maintained steady.Those contributes to reduce amount of sediment deposition and healthy development of Poyang Lake.