Sub air is a life support system. Much better to have lived a healthy life - i.e., make water flow down hill, get in sunlight and breezes, etc. From a 2004 column in Golf Course Industry on the topic. Its late and I am not even re-reading it before posting, but I hope it piques someone's interest enough to be worth the three minutes I spent finding it on my computer:
A Superintendents Drainage Primer
By Jeffrey D. Brauer
Past President, American Society of Golf Course Architects
You have probably installed additional drainage at your course, and may have certainly 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!”
I was recently asked for a “simplified” golf course drainage design criteria, so I‘ll share some formulas I use. First, I recommend that you take care of surface drainage problems with surface drainage, and subsurface problems with subsurface drainage. Spring correction requires 4” (or larger) perforated, gravel imbedded tile drains at the seepage location. However, many superintendents use tile drains to correct surface problems, when grading surface pitch of 2% and preferably 3% to inlets is necessary. Grading around an existing irrigation system is difficult, but I’ve done it and it requires planning!
Your drainage systems won’t need the large pipes used in subdivision work. That’s because engineers size drains for the protection of property, health, safety, and welfare, and typically add a safety factor of a bazillion for good measure. Golf courses usually don’t face critical safety issues, but where these issues arise, an engineer should develop the drainage plans.
On golf courses, immediate drainage of large storms isn’t necessary or cost effective. While I don’t recommend designing for a large storm, I do recommend sizing pipe consistently, so your entire course is ready for play concurrently. You will want to protect every day turf conditions from the effects of nuisance drainage and every day storms by disposing of incidental drainage immediately. Occasional play delays are acceptable in larger storms while pipe capacity removes stormwater. Temporary ponding assists in filtering inputs, so smaller pipes and inlets are environmentally sound and cost effective.
However, submerged turf suffers from oxygen depletion after only a few hours, and faces death in as little as two days if submerged during summer temperatures. Your drainage should handle “typical” storms in about 90 minutes and drain larger storms in a few days. Draining a 2 year storm in 90 minutes (which also drains a 100 year, 24 hour storm over two days) is adequate for most golf course installations.
After laying out a piping scheme, I use the Rational Method to size drainage pipes. The formula Q=CIA where,
Q = Run-off (in cubic feet per second)
C = Co-efficient (% of run-off expressed as a decimal)
I = Intensity Rate of Rainfall (in inches per hour)
A = Acres of watershed draining to a particular inlet
The mathematically astute reader will recognize that this formula really estimates acre-inches per hour. However, by coincidence, that is exactly the same value as Cubic Feet per Second, which is the unit used to size pipe.
To use the Rational Method, you must estimate the percentage of runoff from a rainfall based on site factors. Some typical co-efficient values are Urban/Industrial – 70%-90%, Residential – 50%- 70%, Golf Course – 30% - 50%, and Rural – 10% - 30%. If parts of the watershed area is (or will be) urbanized, you should blend co-efficient values, based on the portion of the drainage area that is in each land use. You should use the higher percentages if you have clay soils, steep slopes, and light turf cover, average values for loam soils, moderate slopes and vegetative cover, and minimum values, if you have sandy soils, flat slopes and heavy tree cover.
Remember, these values are estimates. Some rains will fall on dry soil which will absorb it readily, but other storms will occur when your soil is at field capacity through irrigation or earlier rains. I recommend using higher values, where possible.
“I” is the storm intensity you want to drain, which is usually a two year storm in 90 minutes. In Houston, that’s 2.0”/hour. In Kansas City, its 1.5”/hour, and up north in St. Paul, It’s about 1.0”/hour. These areas are in the “I-35” Corridor, which tends to have intense storms. Thus, you could use these values if you are at similar latitude and have a safety factor. Assuming 50% runoff, the typical Houston drainage acre produces 1.0 CFS, Kansas City acres produce 0.75 CFS, and St. Paul acres produce 0.5 CFS of runoff. While engineers consider other factors, we use these simplified figures for golf courses.
To size catch basins, measure the acreage draining into each inlet, and consult the chart below, which is based on typical light duty golf courses basins, with a safety factor. (Grass clippings reduce capacity!) So, while smaller inlets may have “better aesthetics,” oversize your basins!
Design Intensity in CFS per acre CFS Actual Acres Drained by
0.25
CFS
ACRE 0.375
CFS
ACRE 0.5
CFS
ACRE 0.75
CFS
ACRE 1.0
CFS ACRE
8 in. round grate 0.3 1.2 0.8 0.6 0.4 0.3
10 inch round grate 0.6 2.4 1.6 1.2 0.8 0.6
12 inch round grate 1.2 4.8 3.2 2.4 1.6 1.2
15 inch round grate 1.7 6.8 4.5 3.4 2.25 1.7
18 inch round grate 1.8 7.2 4.8 3.6 2.4 1.8
24 inch round grate 2.8 11.2 7.4 5.6 3.7 2.8
You size pipes similarly, starting at the top of your line, where the pipe needs the same capacity as the first basin. At subsequent basins, the outlet section of pipe must accommodate both that inlet and the water already flowing through the pipe.
Pipe Size Min. Slope CFS Mid Slope CFS Max CFS Slope
4 inch pipe 1.25% 0.2 4.5% 0.4 10% 0.8
6 inch pipe 0.7% 0.6 3.0% 1.33 6% 1.8
8 inch pipe 0.5% 1.0 2.0% 2 4% 3.2
10 inch pipe 0.33% 1.75 1.5% 3.3 3% 5.0
12 inch pipe 0.25% 2.5 1.0% 5 2.5% 7.0
15 inch pipe 0.20% 3.7 0.8% 6 1.75% 11.0
18 inch pipe 0.15% 5.25 0.6% 10 1.5% 16.0
24 inch pipe 0.12% 9.5 0.4% 20 1.0% 30.0
Pipe size is a function of both flow and grade. For example, if the top basin contributes 1.0 CFS, you’ll need a 10” basin and either a 6” pipe at about 3.0%, or an 8” pipe at 0.5%. Smaller pipe costs less, but many situations require larger pipe at flatter grade. If the next basin adds 4.0 CFS, that pipe must carry 5 CFS total, requiring 10” pipe with 3% grade, if available, or a 12” pipe at 1.0%.
The minimum slopes shown are those required for “self cleansing velocity.” If you ignore this, your drainage system will require constant cleaning. (Sanitary Sewer engineers use a minimum “self-cleansing” velocity of 2 feet per second, while drain pipe manufacturers recommend 3 feet per second. I have trouble envisioning storm water flowing less freely than sewage, but I use 3 FPS.) The maximum slope is that which limits scoured pipes and exit area erosion problems from high flow velocity. The mid range allows you to do some mental gymnastics to arrive at correct pipe size for “in between” situations.
I hope this helps you design better surface drainage for your golf course!