Breach growth formula (Water Overlay)

Breaches can grow when water flows from the virtual external water source into the hydrological model.

First, the difference in height of the water on either side of the breach is calculated.

H = abs( max(0, EL - H_b) - max(0, WL - H_b) )

Using the height difference, the breach width increase is calculated.

ΔB = 1.3 * ((g^0.5 * h^1.5) / cs_b ) * log10 (1 + (0.04 * G / cs_b ) * Δt / 3600)

The current breach width is then equal to the last calculated breach width, plus the calculated additional breach width.

B_new = B_old + ΔB

Where:

• B = The total calculated breach width, initially equal to W_b.
• Δt = Computational timestep.

• ΔW = The calculated width increase of the breach.
• Δh = The difference between the height of the water columns on either side of the breach.

• f_m = Material factor, set to 1.3 (average for sand and clay levees)
• g = Acceleration factor of gravity
• H_b = The BREACH_HEIGHT attribute of the breach.
• W_b = The BREACH_WIDTH attribute of the breach.
• cs_b = The critical BREACH_SPEED attribute of the breach.
• w_e = Current external water level.

See also

• Breach