Enhanced slope seepage resulting from localized torrential precipitation during a flood discharge event at the Nuozhadu hydroelectric station

摘要

The Nuozhadu Hydroelectric Power Station,located on the Lancang River in Yunnan,China,represents a fairly typical high dam within a narrow,V-shaped canyon. Its flood control in rainy season requiresconcentrated release of surplus flood water,producing intensified misty rain over the energy dissipation area.This intensified misty rain would spread over a large area and fall on a steep slope (s),producing a higherinfiltration condition lasting for days. This occurrence causes concern over the water table rise and saturationincrease in the slope,especially near the foot of the slope where the stress is often focused. In this paper,wedeveloped a 3-D water table flow model for a fractured granitic groundwater system that is recharged by rainprecipitation. Results show that the precipitation from the flood release could elevate the water table by anamount greater than what would be a seasonal fluctuation. The modeling results provide the basis for furtheranalysis of the effective rock stress in the slope caused by increased saturation,leading to the reduction ofslope stability. This slope-flow study represents one of the first field study cases in this active research area ofintensified infiltration during flood discharge events at large hydroelectric stations with high dams and narrowV-shaped canyons. Its methodology and general conclusions might be generally applicable to other slope siteswithin hydroelectric power stations.