Table 3. Breach Parameter Estimation by using HEC-RAS (Rainy Day) Required inputs in HEC-RAS1 Values Note Top of dam elevation (RL) 155.00 Breach bottom elevation (RL) 137.14 Base of cone of depression Impoundment elevation at failure (RL) 155.00 Initial water elevation Impoundment volume at failure (m3) 1,976,000 Volume of cone of depression Dam crest width (m) 20 Based on design Slope of US dam face Z1 (H:V) 2.3:1 Average slope based on design Slope of DS dam face Z2 (H:V) 4.8:1 Average slope based on design Earth fill type Dam type Dam erodibility Range of breach parameters2 Method Bottom width (m) Side slopes (H:V) Development time (hrs) Von Thun and Gillete (1990) 54 0.5 0.61 Xu and Zhang (2009) 24 1.06 0.99 Notes: 1 Parameters are for a tailings storage dam for Process I (i.e., initial discharge of pond and eroded tailings). 2 Breach parameters for a full breach of a water storage dam with a bottom elevation at RL137.14. Non-homogeneous or Rockfill Homogeneous/zoned-fill dam Medium
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