How to build a putting green using modified techniques
Part 2 - The subsurface drainage
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Shaping is done, looks good? Next step to build a putting green is to add the drainage. For this we will need a method of finding elevation differences. The easiest is using a transit level, which is simply a scope you set perfectly level, and through which you look at the elevation on a measuring stick. The most confusing part of this is that as your height measured on the stick gets shorter, it means the elevation at that point is higher. Now survey the green and find the lowest point or points along the edges of your green. These will become your exit points for the drainage pipe. Next find your high point on the green, this can be anywhere from the middle of the green to a high edge. This will be your high point where the main drainage line will begin.
How to design the drainage
Trace a line from the high point to the exit points. Every 3 meters (10 feet) draw a pipe into that mainline at a 45º angle creating a herringbone pattern (see figure 1.)
Figure 1: Typical Blueprint of a small putting green with drainage lines
At the edge of the green draw in another line that follows the edge (this is normally known as the smile). The next step to build a putting green is to trench those lines. The depth will depend on how far below finished grade you presently are. If you are going to be adding greens mix, you only need to go down about 8 inches. If on the other hand you are working on the final grade, you need to get your drainage down at least 14 to 16 inches to be sure it won’t be damaged by maintenance such as aeration or moving the pin placements. How you go about digging the trenches depends again on means. It can be dug by hand using a 5 inch wide trenching shovel, however, that could prove the be a long and painstaking task. An easier method would be to find a chain trencher to do the digging for you. Another method that is longer and requires a bit of skill would be a small excavator with a 6 inch wide bucket. If you do decide to use mechanical equipment, remember you will need to cross over open trenches in order dig everything, the best way to cross an open trench is by placing boards or plywood over them.
Installing the drainage
The next step to build a putting green is to clean the bottom of the trenches before backfilling them, making especially sure there are no rocks or uneven sections. Then add a little bit of drainage sand to the bottom of the trench to protect the bottom of the pipe. Now you can add the pipe. The industry standard is 4” black corrugated flexible drain tile also commonly known as Big “O”. Ideally you will want to use a pipe wrapped in geotextile to prevent fine soil particles from entering the pipe and slowly clogging it. Another option is to use a drainage stones such as pea gravel or other large size stone that will easily let water pass through. You should buy the fittings for the “Y” or “T” connections and the caps for the ends of the pipe. The fittings aren’t that expensive and will work much better than homemade versions; this isn’t a place where cutting corners will help. Finally before you can cover-up the pipe, be sure to use lots of ductape (yes that all purpose tape even has a use in green construction!) to seal the connections so that debris cannot get into you drains.
Continue to Part 3 of Modified green building techniques
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