Here, you will see the layering in a bunker. This particular bunker has had nearly a foot of sand added in the past. The pipe at the bottom of the hole is obviously plugged and not working properly anymore. Many golf courses each year elect to just add sand thinking this is the correct fix. What they ultimately find is that the new sand is quickly contaminated.
The contamination occurs when the water cannot drain properly and backs up in the bunker. When you see your bunkers full of water your sand is becoming contaminated. Each time water has to be pumped out or even if the bunker drains slowly the water is bringing fines to the surface of the sand. This action causes the condition you see at the right.
The only proper way to correctly handle such a condition is to replace all the sand and drain pipe. The adding of new sand without addressing the drainage problem is an absolute waste of maintenance funds. The sand that is added on top of a situation will last only a year or so. It all really depends on the amount of rainfall.
If you chose to rework the bunker in its entirety, your efforts and money will go much further. A properly drained bunker could last 5-10 years depending on the base material. If you elect to use one of the bunker liners they will last longer. The liners allow excess water to run in the thickness of the mat and thus lessens the chance of contamination. The mats will also help on high faced bunkers with holding the sand in place and eliminates the need to send crew members out after a rain event pushing the sand back up on the faces.
Sand costs on a bunker project is running around 35% of the project. At this rate it does not take long to pay for a total renovation. Sand in not the only cost of a poorly draining bunker. It could take a couple of guys a day or so to pump the excess water out of all the bunkers on your course. In years with heavy rainfall you would never get caught up.
Bunkers consume a lot of time and money. Make your bunkers easier to maintain by having them properly built and never look back. Your golfers, Superintendent, and wallet will thank you.