This trap is best used in a cavern/tunnel setting, where there are tunnels partially covered with water.
Picture a pit-trap covered with a few inches of slowly moving water. When triggered, the trap drops you 10-15 feet down, but not onto your standard spikes. Instead, the trap drops you down into a fast-moving powerful stream of water, 4 feet deep, which runs in a 5 foot tall by 3 foot wide tunnel. The stream flows through a metal portcullis, but there are spikes on the inside of the portcullis, facing in the direction the player is coming from. Splat!
The character who hits the spikes takes 2d6 damage from being impaled. Save vs. Wands for 1d6 dmg. Additionally, any player with less than 16 strength** cannot push his way back off the spikes because the current of the stream is so strong. The best he can do is get his head above water so he doesn't drown. As a result, an additional 1 hp in wound aggravation damage is incurred each round the character is stuck against the portcullis spikes. Spellcasting is, of course, impossible, and the portcullis is not meant to be lifted. It's buried into the rock. It will even be difficult for the characters above to hear the impaled character scream in agony, even if they get the trap door open, due to the roar of the fast moving stream.
** (AD&D versions of stats, adjust for later editions accordingly)