| Ganjiang river basin has an area of 82809 km2, making up about 50% of the Poyang Lake drainage area. It is the the largest river system in Poyang Lake Basin. During recent 60 years, the local government has implemented a lot of afforestation, soil erosion control projects, to protect the ecological environment of Ganjiang river basin. On the other hand, large amount of water conservancy projects were constructed and operated since 1980 s, in order to meet the agricultural, industrial and urban water demand and the utilization of water power resources in Ganjiang river basin. Obviously, all of those intense human activities brought new influnces on runoff and suspended sediment of Ganjiang river. This paper collected long-term measured data at 8 hydrological stations, from 1953 to 2013 for flow, or 1956 to 2013 for sediment. Those stations include Xiashan station, Bashang staion, Julongtan station, Hanlinqiao station, Mianjing station, Jian staion, Xiajiang station, and Waizhou station. We applied hydrograph, flow duration curve, dual water and sediment accumulation curve and Mann-Kendall test, Sen slope estimation, Pettitt mutation detection methods, to systemically analysed variation features of streamflow and sediment at those stations. We also roughly discusseed the main factors influencing changes of water and sediment according to measured rainfall data from 15 meteorological stations within the basin. Results indicated that:(1)A distinct uneven annual distribution was observed on both runoff and sediment, with the peak at June and the minimum value at December. Water and sediment fluxes increased from January to June, and decreased from July to December. Runoff fluxes during the major flood period, from April to June in Ganjiang, accounted for about 49% of that in a year, while sediment fluxes accounted for about 65%. It implies the nonuniformity in annual distribution of sediment was greater than that of streamflow.(2)A regular decadal change was apparent on streamflow for all stations, with 1970 s and 1990 s regared as wet times, and other times as flat water periods. The ratio between the maximum annual runoff and the minimum annual runoff was 4.5-5.7, and variation coefficient estimated 0.28 to 0.33. However, detailed trends and mutation analysis of annual runoff indicated that all stations have no significant tendency or abrupt point. It suggested that complex human activities within the watershed has not yet produced significant effect on annual runoff of Ganjiang River.(3)Different from runoff variation characteristics, suspended sediment has a more apparent interannual change, with variation coefficient estimated 0.46 to 0.62. What's more, an evident decreasing trend can be detected on sediment for all stations during recent 60 years, in part due to a great diminish since 1990 s. Then the abrupt point of annual sediment at the upper four stations, Jian station, Waizhou station came out in 1999, 1990, 1990, repectively. Their relative change magnitude was 47%, 67%, 62%.(4)We also did some further analysis of the flow duration curves and average monthly sediment concentration variation. It showed that the high flow component is slightly reduced and low flow component increased obviously. The high flow component refers to the flow value that is exceeded 5 per cent of the time, and low flow component refers to the flow value that is exceeded 95 per cent of the time. On the other hand, the average monthly sediment concentration significantly reduced, since 1980 s or 1990 s,which was a main driving factor on the sharp drop in the amount of sediment fluxes.(5)Finally, we examined annual precipitation of Ganjiang river basin based on measured rainfall data from 15 meteorological stations. Variation of annual precipitation and annual runoff were consistent. The slightly increased annual rainfall added the amount of annual streamflow of Waizhou station during past 60 years, estimated to raised 0.80×108m3 water per year. Although no evident change observed on annual precipitation, the fluxes of sediment seen a sharp drop since 1980 s or 1990 s. It can be linked with several human activities such as soil and water conservation, reservoir construction. The relationship of annual runoff and sediment also changed a lot due to all these factors.Hence, we can observed the behavior of runoff and sediment evolution since 1980 s were not consistent with that during 1950s~1980s. It was a combined result of precipitation change and intense human activities. All of this could provide reference for water and sediment resource management and relative environmental research. |
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