IMPACT OF THE DANJIANGKOU RESERVOIR ON THE FLOW REGIME IN THE MIDDLE AND LOWER REACHES OF HANJIANG RIVER

With the development and utilization of water resources of Hanjiang River,the flow regime of Hanjiang River has been altered to some extent,and the health of Hanjiang River ecosystem has been influenced to some extent.With the Baihe,Huangzhuang and Xiantao hydrological stations as the study objectives for research of the impact of human activities on the flow regime of Hanjiang River,the study period was divided into two subperiods by the time when the gates of Danjiangkou reservoir were initially closed for water storage.The variations of annual,monthly,daily runoff,and the runoff of wet season and dry season on the middle and lower reaches of Hanjiang River were comparatively analyzed according to the observed data of daily discharges during 1955 to 2006.The result shows that the operation of Danjiangkou reservoir did not affect annual runoff downstream,but led to more even the runoff of wet season and dry season,daily runoff and the monthly runoff distribution downstream,the percentage of wet seasonal runoff decreased significantly,the percentage of dry seasonal runoff increased significantly,the distribution of the runoff was more symmetrical,the frequency of the medium and lower discharge increased,and the frequency of the higher discharge decreased,but the impact was more weaker along with the increase of distance.This paper could provide reference for the assessment of impacts of human activities on the health and stability of Hanjiang River ecosystem.