Breach Evaluation of a Complex 11-Dam System Using Updated PMP with Rain-On-Mesh Hydrology in HEC-RAS

Recent failures of large tailings ponds around the world have resulted in destruction of property and many deaths in recent years. Consequently, one of FTN’s clients asked FTN to perform breach analyses for 11 earthen levees/dams in series under both “sunny day” (SD) breach or “Probable Maximum Precipitation” (PMP) conditions. The analysis was complicated by the interaction between the dams under different breach conditions.

FTN used new methodologies to give more accurate runoff results including using updated PMP data with Rain-On-Mesh two-dimensional (2D) modeling afforded by the US Army Corps of Engineers’ HEC-RAS modeling software.
Results show that a cascade of failures did not occur as anticipated as a result of upstream dam failures. We show that the impact of the dam failures during the PMP did not increase peak flood elevations downstream and present how this was determined using GIS techniques over the 2D mesh.