Hi BEN,
as you know, the breach is indeed trapezoidal, and the width represents the bottom width.
The breach level describes also the bottom level, so it can be the level you want, except that it doesn't make sense to define a breach level which is below the ground level: so that's a restriction. The initial level is the level describing the bottom of the breach right after the initial failure: you can set this intial breach level equal to the dam level (before failure), if you want to model a smooth / continuous breach development. On the opposite, you may assume that part of the dam is intantaneously destroyed and hence that the breach development is discontinuous: in that case, you can define an initial breach level much lower than the dam level.
Best regards,
Mathieu
