Modeling dam deformation in the early stage of internal seepage erosion – Application to the Teton Dam, Idaho, before the 1976 incident

Internal seepage erosion of dams is hidden from view and can cause unanticipated dam failure and calamity. Recognition of dam deformation associated with internal erosion may identify the occurrence of internal erosion and provide early warning to the public on the oncoming failure; but quantitative analysis of dam deformation due to internal erosion is currently lacking. In this study we formulate the early stage of internal erosion and dam deformation by using a numerical model that couples several aspects of the problem, including groundwater flow, erosion and transportation of solid particles, and deformation of the solid skeleton. We apply the model to the Teton Dam of Idaho, which failed in 1976 due to internal erosion. Our simulation shows that the early stage of internal erosion degrades the stiffness of the dam and produces recognizable ground subsidence. It increases porosity and permeability and accelerates flow and internal erosion in a positive feedback process. The predicted magnitude of the surface deformation of the dam during the early stage of internal erosion ranges from several cm to tens of cm that may be detectable with current land survey and space geodesy. Detection of such deformation during the early stage of the internal erosion of the dam should provide sufficient early warning to the oncoming failure. Our result suggests that continuous geodetic monitoring may be an effective measure to detect the occurrence of internal erosion, together with an early warning system, may help to mitigate dam failure and the loss of life and properties.