Assessment of the Breaching Event, Breach Parameters and Failure Mechanisms of the Spillway Collapse in the Swa Dam, Myanmar

The spillway of the Swa earthen dam, constructed in Yedashe Township, Bago Region, Myanmar, collapsed suddenly on 29 August 2018 and resulted in a huge flood to downstream areas causing fatalities and the displacement of thousands of localities. This study aimed to assess the spillway breaching process in terms of the breaching parameters such as the average breach width, failure time and peak outflow, and failure mechanisms. We analyzed the event from the changes in the study site before and after the event and used water discharge conditions from satellite data and water level records during the event. We compared the breaching parameters using empirical equations from past failed events with tested scenarios for failure mechanisms, such as overtopping and piping. According to satellite data, 97% of the storage from the reservoir was discharged, and the peak breach outflow rate was 7643 m(3)/s calculated from the water level records. The selected empirical formulas were applied, and the estimated average breach widths, failure times and peak discharge from the formulas were larger in overtopping and nearer in piping than that of the observed data for the Swa Dam. Thus, a concrete spillway might impact the erodibility rate of breaching compared with concrete-faced and earthen dam types.