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A Landslide Lake was formed in the upstream of Chin-Shui riverbed, which was blocked by materials form several landslides around Taso-Lin mountain owing to a ML 7.3 earthquake on September 21,1999 in central Taiwan. For the possibility of using water in the lake and preventing a dam break as a result of heavy rainfall, a hydraulic model test is presented to analyze how to reduce damages in the downstream of landslide lake . The model studies erosion mechanism , erosion area , erosion conditions , erosion trends as well as hydraulics and transition of bed loads flow from the landslide lake spill channel downward in different reoccurrence peak flow . Some conclusions are made from study as follows: 1、As a result of slope and soil structure of spill channel, the formation of cutting and widening will a long term trends. 2、Mass of soil in slopes sliding to riverbed cause the inter-widening erosion between banks and fluttering flow. 3、The direction of flow of spill channel is fluttered by slides and developed to Chin-Shui Riverbed slowly. 4、Spill channel has a erosion pattern of silting after eroding, The channel is effected by slope and tributary of downstream. 5、Because full of fine sand and silt, Soils on the slope slided down in a mass, so the channel was blocked easily and the water cut off was suddenly. Debris flow will be happened. 6、The huge rocks in the channel are correlated with erosion change of spill channel. 7、Judging from the sand flowing out, risen silting are the development trends in the downstream of tributary, so these effects should be discussed associating with the cross section and sand concentrated flowing out. All the studies mentioned above are provided for reference to manage the area around Landslide Lake.
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