Reexamination of the 2004 Failure of Big Bay Dam, Mississippi

This paper provides a summary of a reexamination of the 2004 failure of Big Bay Dam based on a potential failure modes framework as outlined in the FEMA, Technical Manual: Conduits through Embankment Dams, 2005; and as further described by Ferguson et al, 2012. Of particular interest is the influence of piping and erosion through open defects in the outlet works conduit and how the full failure mode likely developed through a series of backward erosion initiation/continuation cycles that began under the upstream slope of the dam and moved toward the downstream end of the conduit over a period of about thirteen years. Results of idealized 2-dimensional seepage models of the development process are presented that help inform the assessment of this unique combination of failure mode steps. A generalized risk analysis event tree of the failure mode is presented and described.