Friday, September 7, 2012

Simple Math

(Editors Note:  I ran across this "draft" blog from earlier this summer that was never posted.  Recently I had a conversation with a fellow member that followed similar tracks.  So better late than never, circa July 2012.  _Mk)

A member at Tri City posed an interesting question earlier this week as to why we weren't watering more to keep the grass greener.  His comment got me thinking about the limitations of our present irrigation system during periods of extreme heat and drought.  (July was the hottest and driest on record.)

We have all been there.  You can just picture that stretch of I-75 near Chattanooga Tennessee when you just pass by that poor trucker straining to make grade while other trucks seem to effortlessly pull their load past the slow poke.  Ever wonder why?  The answer is horsepower.  The same holds true when it comes to irrigation pumps and I'll explain why.

Our pump station has a capacity of 1500 gallons of water per minute the product of three 50 horse powered motors and pumps.  (Remember this pump station is shared with Tri City.)

Our current system is set up to water "wall to wall" and is set to deliver .14" of an inch of water to greens, tees, fairways, approaches, green banks and roughs if I run it at 100% daily.

.14" x 7 days/week = .98" per week taking nine hours to complete the cycle.  Our water window is 9 PM to 6 AM to avoid maintenance and play as much as possible.

In my book the perfect irrigation system would be able to complete the cycle in six hours and I'll explain why.

During one stretch in Mid July of this year our average ET loss was .28" per day!  ET stands for Evapotransporation.  In a nutshell, it is the amount of soil moisture lost to the atmosphere by evaporating from the soil or trans located through the plant for cooling.  Factors like temperature, relative humidity, solar radiation and wind speed among others determine ET.

So if I wanted to replace the moisture lost on high ET days say .28" per day, I would have to double our systems output to replace that what was lost.  200% x .14" = .28"  Doubling the output also doubles the time.  200% x 9 = 18 hours would now be required to irrigate the golf course to replace what was lost in just one day!  String several days like these in a row and you can see how quickly we fall behind without the help of timely beneficial rains.  That is why irrigation systems are called "supplemental."  They are supposed to supplement what Mother Nature doesn't deliver.

Now why on earth would I want a system to deliver .14" in a six hour day you ask?  Simple math.  Because if I had to double my irrigation output, in this scenario twelve hours, I would rather water between the hours of 8 PM to 8 AM.  The disruption to play and maintenance would be lessened greatly.  I don't know how many golf courses would like to have their course irrigated between 8 PM and 2 PM daily leaving a six hour window of time to play without water flying overhead somewhere.

We do the best we can with what we've got.  There's no other way.  _MK