IMPACT Project Workshop Wallingford 2002 Breach Formation Theme

IMPACT Project Workshop, Wallingford 2002 Breach Formation Theme Formulation of a New Breach Model for Embankments

Introduction Do we need a new model?

The Ph. D Project • Started on 1 st of October 1998 • Ended on the 31 st of January 2002 • Objectives: – Improve the understanding of the process embankment breaching. – Develop a model based on that understanding

The HR Breach Model • Lateral and Longitudinal Breach Growth • Flow Equations • Sediment Transport Equations

Lateral Growth (existing models). • Uniform Erosion • Constant Shape. • Top Width Adjustment • Constant bottom width • Most stable section • Assuming a shape • Slope Instability (some)

Breach Growth (Real Cases 1)

Breach Growth (Real Cases 2)

Breach Growth (Real Cases 3)

Breach Growth (Physical Modeling at HR)

Growth Mechanisms • Continuous Erosion – Computed using a sediment transport equation. • Mass Failure – Shear failure – Bending failure

Shear Failure (1)

Shear Failure (2)

Bending Failure (1)

Bending Failure (2)

Longitudinal Breach Growth (New Model) • The sediment transport continuity equation.

Sediment Transport Equations • Difficult to decide which one? • Selected Equations: – Yang 1979 (Non Cohesive) – Visser 1998 (Non Cohesive) – Chen and Anderson 1986 (Non Cohesive)

Flow Equations • Weir Equation • Flow over the crest and on the downstream face • Bernoulli Equation • Hydraulic calculations on the crest and the downstream face

Material Uncertainty

Composite Embankments (1)

Composite Embankments (2) • Core Failure Modes: – Sliding – Overturning – Bending

Piping (1)

Piping (2) • Processes – Flow through the pipe – Pipe widening and deepening – Failure of the material above the pipe – Failure of the top of the dam – Similar processes to overtopping