Flushing the Faux Flush

For the sake of discussion spanning geography, lets just assume that in most climates, at some point, push-up or all sand greens need to be flushed. Today I’m thinking about the word Flush and what it means to different people at different times. In the field, if I ask 10 supers how much water a flush means to them, I’ll get 10 answers ranging for 10 min to 10 hours. Seriously? The math is pretty easy in the simple form so lets do it together.

Lets say we have 5,000 square feet of a 12 inch rootzone at 45% total pore space. A typical sand based green. That means I have 2250 cubic feet of pore space (sq ft x ft depth x pore space). Water is 7.48 gallons per cubic foot. So to get to Field Capacity in this example we take 2250 x 7.48=16,830 gallons (cu. ft. of pore space x gal per cu. ft =gallons to field capacity). If I fill these pores, pretty soon the forces of gravity take over and much like grabbing the handle on the toilet, BAM, there’s a flush. A rush of air into the rootzone and the bad stuff either hits the drain tile or goes to the next perched water table.

Our 16,830 gallons has to be applied and in this particular example, we have 4 heads covering this green and all 4 do 28 gpm and they are part circle sprinklers. We would double the GPM (assuming that they are exactly half circles…they never are but, we have to have an example). So that’s 4 x 56 or 224 gpm. We need to put out 16,830 gallons so our run time here would be 75 min (gallons needed/gpm=run time).

So if you tell me that you usually run green 6-8 min and today you flushed with 12 min, I’m gonna teach you this math because you are a Faux Flusher…an Irrigation Drag Queen. And this is an on paper calculation, the truth is with things like part circles that are more than 50% arc, leaching fraction and the like, you are probably closer to 120 min in the real world of this example. In fact, I think that the Faux Flush is probably one of the most damaging things that you can do. It often only makes things wetter, never gets to a real flush where the air gets exchanged and the surface actually might become firmer.

Consistently, when I talk about a flush and we see the real numbers, I’ll hear something to the tune of, “If I turn on heads for

more than 4 min, the water just runs off”. I’m sure that’s true with the daily double cutting and rolling and the like today and ideas like venting being something that not everyone gets, infiltration rates are bound to be minimal in the upper rootzone. However, when hydraulics and gravity and adhesion/cohesion take over in the presence of more water being applied, there’s a pull that happens. Think about it from a rain event perspective. The greens always puddle at the start of the rain event, but after several hours of rain, they don’t do it as much. Oh, and does any of this inspire you all with sand amended push-ups to want to have drainage? Not a bad color of lipstick for you to try.

I thought I might stimulate your mind on a pretty important topic. Don’t be a Faux Flushing Drag Queen.

18 Responses to “Flushing the Faux Flush”

  • Dave Wilber:

    @chuck
    There’s a certain amout of water we want flowing through so makes perfect sense. The check method is highly cool.

  • Ken Wheeler:

    I have 58 year old push up greens and depending on the size they 30min to 60min of water once every 3 to 4 days at 28 gpm.The grass is a mix of poa and bent about 60 to 40 poa.I think that is flushing?

    Thanks Ken

  • Dave Wilber:

    @ Ken
    Seems like that’s a flush of about 6 inches of the pushup/topdressing layer. Not a bad move. Wouldn’t it be great if it went deeper?

  • Dave Wilber:

    Have had a couple of folks who paid attention in their irrigation auditor’s class ( I took it too, btw), tell me that I’ve confused Precip rate and GPM. I haven’t. But for the purpose of a 15 min written from the truck blog post, I wanted to make a brief example. I truly understand that a certain head with a certain nozzle at a certain pressure does a certain GPM no matter what. And I get that if you make that head’s arc 180 degrees or 45 degrees or 360 degrees you affect the total volume of water that goes in a given area for a given amount of run time.

    Those things are all irrigation 101 and everyone should learn them, I agree. The numbers on a page or in the computer are great too…but this is field work and so, there are variables. If you really wanna know, catch cans are very very easy and pretty darn accurate if you use enough of them and get enough data. We’ve saved a lot of challenged greens that way.

    The point here is about the actual flush and how much water really needs to be used to get that. It’s a technique that works well and of course, with a degree of modification, it works even better when fit to an individual situation.

    Really do appreciate all the comments, some more constructive and better written than others. That’s OK. It’s July. I get it. So should you.

  • Nate Jordan:

    Excellent!

  • Bryan Morison:

    I’ve always tried to “flush” during a rain event. Seems crazy to water greens while raining or after a rain storm. In Dave’s example of a 5,000 ft. green needing 16,830 gallons of water for a flush, if I do the math backwards this converts to 5.4″ of water. That is one hell of a rain storm for us folks here in Colorado. I’ll hope that the 45% pore space is somewhat filled with water from previous irrigation cycles (or rain water). One cycle of 75 min or 120 minutes may still only be a “faux flush”, it all depends on how much water is whithin your greens profile prior to deep cycle.

  • Hi Dave,

    I have been thinking about this for some time and it really makes a lot of sense. So to put this into practice how would I determine the pore space for 30 year old push-up native sand greens (poa/bent mix stand)? I want to start this ASAP and could use a little help with my numbers.

    Thanks,

    Andrew Hardy
    Superintendent
    Pheasant Run GC
    Sharon, Ontario, Canada

  • Dave Wilber:

    Andrew,

    Best and most complete way is to send in a sample to a Physical Testing Lab. You can get this fairly cheap. Just ask for total pore space, but take into consideration the upper 6 inches and the lower 6. If it was me, I’d get Total Pores on each depth and make some moves accordingly.. If you want to do some guess work, then start at 30-35 as a low and 40-45 as a high and see how that works out for you. Hope this helps!


Archives