R655-11-11B. Breaching of Dam

If a dam is to be breached the following minimum criteria should be met:

1. The flowline of the breach should be excavated down to natural ground or stabilized at the top of the silt level. In most cases grade control and drop structures will be required to avoid mobilization of reservoir silts and debris.

2. The breach should be designed to pass a flood with a return interval of 100 years without backing water up in the historic reservoir more than five feet.

3. Regardless of hydraulic requirements the bottom width of the breach will be one half the structural height of the dam with an absolute minimum of 10 feet. Additional width may be required by the State Engineer in areas where beaver activity occurs.

4. Breach side slopes must be flat enough to hold the slope when saturated, with an absolute minimum of one vertical on one horizontal. In areas where there is significant human travel, the minimum side slopes should be one vertical on two horizontal.

5. The exposed banks and bottom of the breach should be protected with riprap, vegetation, or other suitable means to prevent downcutting and lateral slope erosion.

6. Barriers should be placed on the original dam crest to warn any possible traffic on the crest of the breach.