Hi. See https://wiki.openstreetmap.org/wiki/Notes and especially note the sentence 'Be clear in your information ... '. As you note, the river is overflowing now. However it does not say where or how. That is insufficient information, and is not possible for anyone for anyone but a local to change the map. Even if you had provided the data, the extent of flooding may have changed by the time someone got round to considering mapping it. You have local knowledge, but are unable to make this change. So, sure it can be left to see if anyone else can change things usefully. But you should make sure that you remove the note as and when it becomes irrelevant. Meanwhile it will slow down me and other editors like me who scan all notes in an area that are clear enough to be actioned without local knowledge. Thanks. 
