Usually the flood season produced a "good Nile," just the right amount of water. What might be the consequence of a "bad Nile" - too much or too little water?

A "bad Nile" is a lack of water or too much water, so possible consequences include:

Famine (from crops dying)

Destruction of property (from flood waters)

and much more. However, this type of question normally references something in the text, so I suggest checking that section to see if a specific example was ever given.