Webinar: Re-examination of the 2004 Failure of Big Bay Dam, Mississippi

This webinar will review the 2004 failure of Big Bay Dam.  A potential failure modes framework was used to make the forensic root-cause assessment based on data and information provided by the State of Mississippi.  A detailed timeline of the failure obtained through review of court proceedings will be presented including the appearance of a number of distress indicators, the seriousness of which were not recognized and acted upon by the Owner and the owner Engineer.  Of particular interest is the influence of piping and erosion of highly erodible fine sandy silt and silty fine sand through open defects in the outlet works conduit. 

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.  The rapidity of the final steps in the failure mode development leading to breach of the dam are quite stunning and serve to reinforce the importance of detecting and mitigating seepage distress in embankments as early as possible in the development process and prior to later stages of continuation/progression when adequate time or intervention methods are not available to stop the failure process.  A generalized risk analysis event tree of the failure mode will be presented and described.