The river disturbances depended on the factors, such as discharge and sediment discharge change, river bed change, channel dredging, artificial revetment and eco-corridor interception etc., it brings about the river ecosystem change because of the physical environment change as decrease and simplification of biological species, and population reduction. But the researches on river disturbances is insufficient, also standardization of the evaluation system dont be builded up. After all the foundation of rivers restoration is not enough actually. The purpose of this study is to investigate analyze physical river disturbance in river reach of Namgang-dam downstream, because dam construction impacted on the downstream hydraulically and morphologically.
Therefore 17.0km reach of Namgang-dam downstream was selected as stream reach to assess river disturbance by dam construction and these reaches were investigated and analyzed on channel geomorphologic and hydraulic characteristics. The results are as follows.
In the long term, the bed slope of thalweg was degraded in dam downstream generally, specially bed slope was mild and channel was channelized as gravels due to the erosion trend and amoring.
In order to maintain ecological environment, discharge of instream flow have to secure about 4∼5㎥/sec habitually, flushing discharge was evaluated as about 400 ㎥/sec.
Future, the counterplan of instream flow constantly and sedment feeding have to worked out carefully for restoration close to nature river.