Looks like something from the 70's

A couple comments.

1. On the next one, I'd run a chain (like an old swing set chain or the like) through the main structural PVC long enough to touch the bottom on each end before adding the spines.
2. Put a cinder block on each end of the chain when sinking it

That way, it will stay pretty well in place where you put it, unless a flood current moves it, or an anchoring fool moves it. It will also help keep it in place if the ends start to break for any reason (the chain through the whole thing will hold it together). Simply attaching blocks to the end, if the end breaks, it's likely to move.