Overtopping and Liquifaction
One of the most common causes of failure is overtopping by flood waters. Overtopping typically results when the volume of run-on entering an impoundment from improper diversion of surface water flows or excessive storm water flow exceeds the capacity of the impoundment. Because tailings embankments are constructed of highly erodible materials, the friction caused by rapid flow over an unprotected embankment crest may quickly erode a gully in the fill material, allowing sustained release to occur. Additionally, a rapid increase in pore pressure associated with large storm water inflow may result in the liquefaction of unconsolidated impounded sands and slimes. Sustained high flow over the crest of an embankment can thus result in a major failure of the overall impoundment within minutes.