The ones in this community are nice, 3-4" river rock, but the landscapers often were more often looking at appearances instead of utility. I had already re-routed mine, where the water around my front courtyard drained straight down hill instead of the nice, 'pretty' angle the original path had followed. I had to be careful that today's flow wasn't great enough that it flows 'around' the rocks, and digs out a new channel beside them!
Charlie