Modeling Approach for Earthen Dam Breach Analysis in North Yamar Dam, Myanmar

In case a Dam breach occurs, it is hazardous for lives, properties and environment in downstream extents. Dam break studies are necessary for forecasting of flood disaster and evaluation of hydrological safety among dams. To investigate possible inundation extents and breach outflow, an experimental study for both overtopping and piping failures was performed in the North Yamar Lower Dam constructed across Yamar creek in Pale township of Sagaing Region. This study is to examine the applicability of hydraulics and hydrologic models, HEC-RAS (USACE Hydrologic Engineering Center’s River Analysis system) and HEC-HMS (Hydrologic Engineering Center’s Hydrologic Modeling System) upon Dam Break. One-dimensional HEC-RAS model was applied in collaboration with HEC-HMS model to predict the potential flood risk due to different breach modes. The extreme hydrological event such as possible maximum flood event (PMF) was considered for the overtopping breach and sunny day piping event for piping breach. Dam Breach outflow hydrographs were generated by HEC-HMS individually and imported them into HEC-RAS for downstream flood estimation. The unsteady mixed flow simulations were performed by HEC-RAS and ArcGIS (Geographic Information System) was used to produce an inundation map based on simulated water surface elevations and extents. The models were calibrated based on the historical floods happened in North Yamar Dam from 2005 to 2017. By scenario analysis for with and without emergency spillway, overtopping breach influenced on different consequences whereas piping affected not much differences. The probable peak discharge would be over 7,000 m3/s and 3,800 m3/s respectively

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 m3/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