Here are my two installments on Cybergolf regarding a drainage primer.....
You have probably heard the old engineering saying, “Toot the horn at all crossings.” No, wait, wrong kind of engineering. The one that says there are three rules to civil engineering: “If you can’t say something nice . . .” No, wait, wrong meaning of civil . . . “Drainage, Drainage, and Drainage!”
“They” also say that a golf course has either too much water (poor drainage) or too little (drought or poor irrigation) most of the time. Perhaps once a day the turf has “just the right amount” of porridge . . . I mean, moisture! So, it’s hard to give a “simplified” answer to that question about golf-course drainage design other than YES! However, I’ll share some simplified drainage concepts I use.
First, you take care of surface drainage problems with surface drainage, and subsurface problems with subsurface drainage.
Subsurface springs require correction with 4-inch (or larger) perforated, gravel-embedded tile drains at and just above the seepage location, to catch flowing subsurface water just before it exits the ground. These do occur regularly, but are not usually the typical drainage problems you face, and yet, many use these tile drains too often.
They are not efficient at correcting flat gradient problems, which are far more common. All turf areas need surface pitch of at least 2 percent, and preferably 3 percent, to natural or installed drainage outlets. Where fairways are flatter than that, we strip the topsoil and re-grade the area to achieve suitable slopes. On renovations, it’s even possible, but difficult, to grade around an existing irrigation system to achieve proper drainage, but I’ve done it!
I use more catch basins than some architects to assist grow-in. Surface drainage concentrates to gully-washing speed in about 300 feet of flow, so I place catch basins every 275 feet to prevent those long ruts often found on even mature fairways. Even after establishment, long swales tend to stay wet, even if ruts are fixed. I prefer more elaborate drainage systems, rather than relying on Mother Nature to “do her thing.” No one wants to wait for perfect conditions to play golf any more. Under-drained golf courses don’t add drainage every year, just the ones whose digits end in 0 through 9.
Golf drainage systems don’t need the large pipes used in residential subdivisions, where engineers’ size drains for the protection of property, health, safety and welfare, typically adding a safety factor of a bazillion. However, any dam or structural fill should be protected against larger storms. For most of the course, it isn’t necessary to immediately drain in large storms on golf courses. In fact, using small pipes and inlets to create temporary ponding helps filter chemical inputs, so smaller pipes and inlets are environmentally sound and cost-effective.
Turf usually suffers more from the constant moisture-associated nuisance drainage and small storms, which should be disposed of quickly. Nuisance drainage often comes from surrounding housing, regardless of actual rain. On subdivision golf courses, we “cut off” drainage from surrounding housing before it hits critical fairways, greens, or tee areas, treating key areas like an engineer raises a road to prevent water from crossing it. We accept that the far roughs may be at less than their best.
However, submerged turf suffers from oxygen depletion after only a few hours, and faces death in as little as two days if submerged during a hot summer. Golf-course drainage systems should handle the storm expected once every two years in a few hours and drain larger, 50- or 100-year storms in about two days. Obviously, some courses are situated on flood plains where there is nowhere for those flood waters to go and this may not always be possible.
Whenever we can afford it, we use bigger pipe sizes for faster drainage. It’s a bargain, because drainage capacity increases with the square of the pipe radius, so doubling the pipe diameter increases cross-sectional areas four times. Pipes on steep grades flow more than those laid flat. We design systems for the steepest possible grades, or use larger pipe if it must be flatter. For example, a 12-inch pipe at 1.0-percent grade carries the same amount of water as a 10-inch pipe at 3-percent grade.
Similarly, every size pipe has a minimum and maximum pitch, with the minimum being that which allows water to flow at 3 feet per second, which carries the sediment through the pipe and keeps it clean. Providing too much pitch may cause the water to exit the pipe so fast that it causes erosion problems, and this should also be avoided.
We do allow unusually heavy rains to pond around catch basins and delay play temporarily, figuring that at least half the large rains occur at night or last all day, and that smaller drains actually have marginal impact on revenues. Consistent drainage, allowing the entire course to open back up for play concurrently, is desirable, because golfers may wait out a storm anywhere on a course.
Most architects prefer to concentrate on the more artistic aspects of design. But without proper drainage, those designs just don’t look as good in real life as they do on paper!