I've heard "dam" metaphors used in connection with emotion---the "dam breaks" and the pent-up emotion in a person is expressed, usually with crying. (Perhaps the connection is all that water? :)) There isn't any standard "correct usage" as far as I know, just the description of a dam in various stages of stability (breaking, about to break, broken with water pouring through in a great flood, etc.) used metaphorically.
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