Seymareh dam and hydropower plant project is located in western province of Ilam, in Iran. This concrete arch dam with 178m height and 196 m crest length is to be placed on Seymareh River, the axis of which is located on the north wing of an anticline including Asmari limestone layers. The dramatic variation of dip angle of bedding in this part of anticline has created many fractures that result in slides. In October 1st 2003, when excavation in the left bank was being operated to construct an access road to the valley, a large landslide triggered on the top of power tunnel intake. The landslide complete in November 10th 2003 few hours after an intensive rainfall by leaving some 300000 m3 mass of debris. The sliding was a planar failure on a thin marly limestone of 26° dip and 40 cm thick. Due to the future location of water intake structure at the entrance part of power tunnel, it was quite vital to save this structure from any further movements of the debris left by the landslide. Further investigations showed that this is possible to keep debris in place by flattening the material in forms of stable slopes and berms. In order to decrease the remedial costs, the new recommended method of screening analyses for seismic stability proposed by SP117 Guideline in southern California Earthquake Center (2002) was adopted. Finally using this method, a slope design with almost minimum costs was achieved. This paper contains a description to geotechnical conditions, the history of landslide, and remedy works to protect water intake structure
