Abstract
In August 1969, heavy rainfall caused a large landslide with a sediment volume of 5-6 million cubic meters in the Roukazawa Watershed, a tributary of the upper Kurobe River. The Roukazawa Landslide was monitored from 1969 to 1994 using aerial photographs to observe topographical and vegetation changes. Gradual expansion of the landslide area was detected over the 25 years; relatively rapid expansion occurred in the first eight years. Vegetation did not invade the landslide area until recently. Yield sediment flowed downstream as debris flow, and the height of the streambed increased by 32m with deposition of some of the yield sediment at the junction of the Roukazawa with the main channel of the Kurobe River, and the width of stream increased considerably. Changes in the area of deposition were also evident from the series of aerial photographs. Twenty-five years after the slide, several types of vegetation had become established, and the stream channel had returned to nearly the same width as before the debris flow.
