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Dam Breach Parameter Calculator

Average breach width, side slopes, and failure time for embankment dams by the three standard regression sets — Froehlich (2008), Froehlich (1995), and MacDonald & Langridge-Monopolis (1984) — for overtopping or piping failure modes. Use the results to set up the parametric breach in HEC-RAS, then estimate peak outflow with the breach peak discharge tool.

ac-ft
ft
—ft
—hr
—ft
—hr
—yd³
—hr
—H:1V

All regressions are computed internally in metric per the source papers and converted for display. Vw is storage above the final breach bottom at failure; for MLM, Vout ≈ Vw and hw ≈ hb is assumed (document your definitions). MLM Ver uses the earthfill equation; the breach cross-section is then constructed to erode that volume with 0.5H:1V side slopes. These are regression estimates with wide scatter — run a sensitivity analysis, not a single set.

$$ \text{F95: } \bar{B} = 0.1803\,K_o V_w^{0.32} h_b^{0.19},\; t_f = 0.00254\,V_w^{0.53} h_b^{-0.9} \quad \text{MLM: } V_{er} = 0.0261\,(V_{out} h_w)^{0.769},\; t_f = 0.0179\,V_{er}^{0.364} $$
Vw, Vout m³ · hb, hw m · B̄ m · tf hours (F2008 tf in seconds, converted) · Ver m³.

Failure-mode factors and side slopes

Recommended parameters by failure mode (Froehlich 2008)
Failure modeK₀Side slope z (H:1V)
Overtopping1.31.0
Piping / internal erosion1.00.7

Worked example

Example — small high-hazard embankment, overtopping

Given: Vw = 500 ac-ft (616,800 m³), hb = 30 ft (9.14 m), overtopping (K₀ = 1.3).
Froehlich 2008: B̄ = 0.27 × 1.3 × 6168000.32 × 9.140.04 = 0.351 × 71.3 × 1.09 ≈ 27.3 m ≈ 90 ft
tf = 63.2 × √(616800/(9.81 × 9.14²)) = 63.2 × 27.4 ≈ 1,730 s ≈ 0.48 hr
Froehlich 1995 (K₀ = 1.4 overtopping): B̄ = 0.1803 × 1.4 × 71.3 × 9.140.19 ≈ 27.4 m (90 ft), tf ≈ 0.41 hr — the two Froehlich sets agree closely here
Model a ~90-ft average breach width forming over ~0.5 hr with 1H:1V side slopes; check sensitivity against MLM's slower time.

References: Froehlich, D.C. (2008). "Embankment Dam Breach Parameters and Their Uncertainties." J. Hydraulic Eng., 134(12). Froehlich, D.C. (1995a). "Embankment Dam Breach Parameters Revisited." Water Resources Engineering, ASCE. MacDonald, T.C. & Langridge-Monopolis, J. (1984). "Breaching Characteristics of Dam Failures." J. Hydraulic Eng., 110(5). Wahl, T.L. (1998). Prediction of Embankment Dam Breach Parameters, USBR DSO-98-004. USACE, HEC-RAS Hydraulic Reference Manual, dam-breach chapter.

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