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(1) The department's hazard determination shall be based on the consequences of dam failure, not the condition, probability, or risk of failure.

(2) A dam must be classified high-hazard if the impoundment capacity is 50 acre-feet or larger measured at the maximum normal operating pool, and it is determined that a loss of human life is likely to occur within the breach flooded area as a result of failure of the dam.

(a) Loss of life is assumed likely to occur if the following structures are present or planned for as a matter of public record or notice in the breach flooded area:

(i) occupied houses and farm buildings;

(ii) stores;

(iii) gas stations;

(iv) parks;

(v) golf courses;

(vi) stadiums;

(vii) ball parks; and

(viii) interstate, principal, and other paved highways, including railroads, highway rest areas, RV areas, and developed campgrounds. Excluded from this list are unpaved county roads and all private roads.

(3) For purposes of the hazard determination classification in this section, the following apply.

(a) The breach flooded area is the flooded area caused by a breach of the dam with the reservoir full to the maximum normal operating pool.

(b) The evaluation of the effects of flood inundation will continue downstream until the flood stage is equal to that of the 100-year floodplain.

(c) The breach flow hydrograph and downstream routing of the breach flows will be estimated by the department either by visual determination or dam breach modeling techniques.


History: 85-15-110, MCA; IMP, 85-15-209, MCA; NEW, 1988 MAR p. 2489, Eff. 11/24/88; AMD, 2012 MAR p.1844, Eff. 9/21/12.

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