This is the answer to the question Henry E asked a few times in recent comments on the blog. I wanted to answer this one with a full blog since the answer is not short. In the Banff blog I mentioned that the soil is too light and too stony to have an exposed soil lip. This is a problem at a lot of courses, yet common practice is to have a soil edge to create a clean sharp line. The problem of course is that the soil lips break down and contaminate the sand and the erosion is the main cause of lost bunker lines. That’s why I try to almost always encourage clubs to go with a living grass lip.
There are four techniques to accomplish this. The first method comes right from the origins of golf – the revetted face. You don’t have to use this technique up the entire face. You can create your bunker with typical flowing lines or steep slopes leading in and still create a small shelf right where the sand meets the soil. In that location you add three to four rolls of sod stacked on top of each other and then pull the soil over the top till it has a low 6” revetted edge. You now have a living 6” lip on your bunker.
Method number two, used at St. George’s in the bunker restoration was to shape the bunker with all the faces and noses, then hand trim out a flat ledge where the sand meets the turf. On the ledge we placed a topsoil filled burlap bag. This created a bunker edge that rounded down into a vertical lip. The bunker lip now has far more organic than the rest of the soil which helps with water retention and establishes must deeper rooting. The shape of the bag created a natural round shape and a vertical interface with the bunker. The sod was simply stapled into the bag to ensure the form stayed together. The burlap bag roots and disappears in only a few months.
The next method is to hand shape the entire edge – this was done at Weston when I did the bunker renovation. This is accomplished if the natural soil is tight enough to hold together. If not a clay topsoil is used to provide a stable enough material to build a bunker lip. The bunker is shaped by mini-excavator and then the bunker face is topsoiled and machine packed. The bunker lines are then cut out by hand – by me – and the excess topsoil is removed. The bunker edges are hand shaved until they are round enough to be sod. The grass is pinned over the soil and into the bunker to ensure stability and avoid erosion. The sod is trimmed out after rooting leaving a vertical sod lip.
The next method is called undercutting. This is done to an existing bunker and involves hand cutting the sod on the face and pulling it back and up the slope. With a shovel you remove around 6” of the soil from behind the bunker lip – usually into a bucket or gator depending how easily you can access the bunker face – until you have a pocket behind the original edge. You then fold the sod back down in tamping it into the face leaving a vertical face of living sod. This sod has an established root system and needs little time to firm up and because of the established grass mixture is usually resilient to droughty periods.
Henry – you have your answer – but I also feel like I shared some things that I didn’t want to.