When you see a dam in a dream, then such dream indicates the feelings that have not been expressed. If the dam was bursting, then it means you are unable to manage your thought and emotions, therefore the anger shows off to those you are surrounded by.
Dream dictionary: bursting a sachet of water dream meanings
When you dream of the hydrant, then such dream indicates the recreation and new start at some point of your life. Perhaps the unconscious mind gives the signal, that you are ready to start all over again. When you see a bursting fire hydrant, then such dream indicates the huge explosion of your emotions.