Having walked Oakmont for a couple of days, I came away impressed with a number of features, but it was the shallow ditches that I found most striking. You don't see them on other courses, but at O they are on almost every hole. In virtually all cases they run parallel or obliquely to fw center lines.
Oakmont has let tall wispy fescue grow up in them. I find the look appealing. Except after a rain, they stay dry.
It strikes me that O's little ditches offer a number of advantages. They make for an interesting hazard, in the sense that recoveries are possible if well executed. They do not call for penalty strokes as a creek would.
They are easy to build and maintain. Best of all they facilitate drainage. None of those things is true of a traditional sand bunker.
Why don't we see more little ditches (or is 'trenches' a better word?) like those at O? I'm having trouble thinking of a downside to them, while I can think of several advantages, both as a design feature and as an aid to draining low spots.
Bob