Possible Clues:

• Such as Niagara
• Steep descent of a river
• Display of flower power coming down?
• In the north, force deployed after breaching part of defence
• Sudden drop of current -- flaw later rectified
• Cascade, force
• Raft we all abandoned — unnavigable part of river?
• Force wife, after adjusting, to meet everyone
• Cascade, and a feature of 17-, 22- and 46-Across?
• Perpendicular descent of a river