Shouldn't proper bunker construction & maintenance eliminate the need for such a situation?
Dave,
That depends on what you consider proper bunker construction. Some courses import sand. In many cases, this sand has been washed, bleached (or dyed), and highly refined for uniform grains. This sand is then placed into a hole with a liner. This liner can be many different materials. What you'll find most common is either a fibrous membrane tacked into the bunker or sod used as a bunker liner. Under this liner you'll find a fairly uniform bunker bottom with some type of drainage installed; most likely in a herringbone pattern using a french drain technique. I would argue that this process is the most common in the United States. Certainly our friends in GB&I have different techniques to include the sod-faced flat-bottomed bunker.
At places most associated with the modern links style and built on sand (examples include Bandon, Ballyneal and even Chambers Bay to a lesser extent) a much more natural technique is used. The bunker is dug, and the remaining natural sand becomes the bunker. Some hand work may or may not be done to make the bunker more aesthetically pleasing, but the wind and water shape the bunker over the course of the bunker's life. They evolve. Based on the natural sandy soils, installed drainage is minimal. In some cases I am sure there are bunker liners, but you'd be hard pressed to identify which ones have them just by looking. I am sure that Chambers has a few liners, but I'm not sure about Bandon, B'neal, Sand Hills or Dismal.
So, why have liners? The liner does exactly what it sounds like. It lines the bunker and forms a water permeable barrier between sand and soil. This protects the drainage system if there is one. But it also prevents surface migration of things that aren't sand. This could be soil not associated with the bunker that you don't want migrating into the sand as well as for pebbles and rocks.
As previously mentioned, Chambers Bay is built on a former aggregate mine. This aggregate was refined into rip rap, gravel, construction material, and sand. There are many bunkers at Chambers Bay where surface migration of rocks and pebbles is a real issue. This is related to two things 1) lack of a bunkers liner between the "native" soil and bunker sand and 2) the fact that its a former aggregate mine.
Bottom Line: The pebbles and small rocks in some of the bunkers at Chambers Bay has nothing to do with bunker construction. It is a result of the sand used (refined sand from the site itself), the sheer number of rocks/pebbles on the site, and the inefficiency of lining every bunker on a colf course with 18+ acres of sand on it.