Here is another installment of exTRAPaganza, our Thursday over-the-top trap series.
A large concave wall is here. A large diamond is set into the wall.
The wall is a dam, and the diamond protects the dam. It is hard to remove, but can eventually be pried off. However, the dam is very old, and once the diamond is removed, the dam materials age very quickly, causing the dam to break.
All targets in a 200 foot line in front of the wall must make a very hard Dexterity saving throw. On a failure, they are pushed 200 feet away, take massive bludgeoning damage, and are being carried along in a torrent of water.
The diamond radiates enchantment and abjuration magic if checked.