"The rocket exhaust is directed into a flame bucket or trench. The flame trench is designed to redirect the hot exhaust to a safe direction and is protected by a water deluge system that both cools the exhaust and also reduces the sound pressure level (loudness). The sound pressure level of large rocket engines has been measured at greater than 200 decibels — one of the loudest man-made sounds on earth."
Maybe for fire-fighting? Seems a little close for that though, if something went wrong it could be in the middle of it. I can't think of anything else though.
Edit: Maybe it feeds some sort of un-manned fire suppression system? That would be pretty smart.
