Hey Rhett,
The RainBird Drip Calculator works well for me. You put in all your parameters and it will give you a recommendation. RainBird's 0.6, depending on the layout, is usually 0.43in/hr.

Here's the link: http://www.rainbird.com/landscape/resources/calculators.htm. Go to Landscape Dripzone Calculator.

 

Your calculations are correct. Drip irrigation can have a surprisingly high precipitation rate when using tight spacing with 1.0 GPH emitters.

92.25 X GPM / Total Area = inches/hour

Or sometimes for Drip Irrigation we use:

231 X GPH / (Spacing x Distance) = inches/hour

http://www.hunterindustries.com/support/how-would-you-calculate-application-rates-using-drip-line

Example:
Take an area that is 60 feet x 10 feet = 600 square feet
Emitter = 1 GPH
Emitter Spacing = 12" (1 foot)
Distance or Row Spacing = 12 " (1 foot)
Total GPM = 10
(Hint: 60 emitters x 60 feet = 1 GPM)

Calc #1
96.25 x 10 (GPM) / 60' x 10' = 1.604 inches/hour

Calc #2
231 x 1 (GPH) / 12" x 12" = 1.604 inches/hour

Same result, just using two different methods.

 

Your calculations are correct. Drip irrigation can have a surprisingly high precipitation rate when using tight spacing with 1.0 GPH emitters.

I agree with HTG.

In my involvement with people outside our industry like water purveyors and environmentalists, I find that they advocate drip and low volume because it is widely 'known' that drip is more efficient due to its slow application rate. It is not widely known that the application rates can as high or higher than sprinkler irrigation.

Don't get me wrong. I like drip in the right place and under the right management. However, drip is not a silver bullet for water conservation. Efficient irrigation is the result of four things done well; design, installation, maintenance and management. If you accomplish only 3 of those 4 there is a good chance you are simply wasting water more efficiently than ever before.

 

what about distribution uniformity?

Is it likely that a spray head area with the the same precipitation rate as a drip area might be superior to the drip area in being able to more evenly spread the water onto the surface?

It seems it would?

but then again im basing the assumption soley on past visual experiences:
that is, that it seems the wettest place on a drip zone is directly under an emmiter, the driest spot being inbetween the drip laterals , farthest from an emitter.

in comparison to drip, spray heads seem to wet the all parts of an area in only a couple of seconds time.

 

what about distribution uniformity?

Is it likely that a spray head area with the the same precipitation rate as a drip area might be superior to the drip area in being able to more evenly spread the water onto the surface?

It seems it would?

but then again im basing the assumption soley on past visual experiences:
that is, that it seems the wettest place on a drip zone is directly under an emmiter, the driest spot being inbetween the drip laterals , farthest from an emitter.

in comparison to drip, spray heads seem to wet the all parts of an area in only a couple of seconds time.

This response could be an entire course in a college level class, but, of course, I will give the over-simplified shorter answer.

Distribution uniformity:
Spray head distribution uniformity is probably not as high as most people assume. Emission rates from emitters are probably not as consistent as most people assume. Variability abounds. In general, I feel better about uniformity of application with drip than I do with spray heads. Drip also reduces other losses like the wind drift and evaporation of water as it flies through the air.

Sprays vs. Drip:
You asked about which method would better deliver the water to the plant. The short answer is that it depends. The factors to consider are (at least): What plant are you irrigating?; what are its water needs; for example, irrigation interval?; What is the shape of its root zone?; Is the entire landscaped area covered with plants and roots or are there plants and roots with spaces in-between with no roots?; What is the soil type and the resulting lateral movement of water in the soil? What is the spacing of the emitters on the line and the spacing between the lines? Of course, there are many more that are also important and I bet others will suggest what they are.

Visual observations versus a thorough understanding of Plant, Soil, Water Relationships:

Seeing is believing, right? You observe that spray heads wet the top surface the soil quickly in what appears to be a uniform manner. Is that what is really happening? Probably not. This is why we have can tests to measure actual distribution uniformity.

Is Distribution Uniformity the one and only thing to consider?:
No. Dr. Michael Dukes with the University of Florida conducted a study about 8 years ago that showed that once 65% DU is achieved, further improvement in DU has a small benefit to delivering water in a uniform manner to the plant roots in the soil. This is due to the lateral movement of water in the soil. This is good information to consider as we make our trade-offs in the design process. For example, should I choose this sprinkler that has a 75% DU (in a zero wind building) but 50% of its water falls outside the target zone in a 6 MPH breeze or should I choose the 65% DU sprinkler that loses only 25% of its water outside the target zone in a 6 MPH wind?

I could go on all day, but that is not what this forum is about. Again, the short answer to your question is, it depends.

 

Were any studies done with head spacing geometry? Old product catalogs from the brass impact head days had diagrams and numbers for triangular spacing, without any insistence on head-to-head layouts.

 

True, cant have water spilling onto the mall's floor.

 

Were any studies done with head spacing geometry? Old product catalogs from the brass impact head days had diagrams and numbers for triangular spacing, without any insistence on head-to-head layouts.

The Center for Irrigation Technology at California State University - Fresno offers software that takes a distribution rate curve of a sprinkler and allows the user to set the distance between heads and the arrangement of the heads (triangular/rectangular). It then calculates, Christiansen's Coefficient of Uniformity, Distribution Uniformity and Distribution Uniformity - Low Quarter. It also generates a Densogram which is a graphic depiction of the application of water in the field of study.

People have used this to 'study' countless combinations of sprinklers and spacing arrangements.

Head to head spacing is a great 'rule of thumb.' However, it is not law. A sprinkler with a 'robust' distribution rate curve is pretty tolerant of different spacing distances. The closer the distribution rate curve is to a smooth, triangular shape, the more robust it is and less sensitive to variation in spacing distances. So, a competent designer with enough information and tools could confidently space some heads in some applications beyond head to head and have great results. Nearly everyone does not have this at their disposal, so the rule of thumb applies.

 

heres the densogram my program shows

 

heres the densogram my program shows

Looking good!

 

heres the densogram my program shows

Looks like you are getting 100% coverage BUT there are definitely areas getting more and less water. Look for where 2 heads overlap vs. 3. Those would be different.

 

I worked for a company back in the late 80's that guaranteed "100% moisture coverage" :laugh:

 

as opposed to 99% moisture and 1% radioactive waste ?

 

heres the densogram my program shows

It's wrong. It is physically impossible to get 100% uniformity on that design, either on paper or in the field.

 

Oh i knew it wouldnt be Kiril approved lol.

one thing i dont understand about that particular densogram is that you will notice it doesnt correspond exactly to the radius' of the circles, rather, it makes nearly a perfect rectangle. odd.

 

Its a very poor densogram.

 

Its a very poor densogram.

Other than as interesting things to look at, I have not found a truly useful purpose for densograms. The DUlq and Scheduling Coefficient results are much more useful.

 

Other than as interesting things to look at, I have not found a truly useful purpose for densograms. The DUlq and Scheduling Coefficient results are much more useful.

They are just another tool. I usually use them to point out low density coverage in irregularly shaped areas. On the LandFX module it will also give the more specific DU calculations etc.

 

One of the reasons to be concerned with precipitation rate is to reduce or eliminate water waste through run-off. As such, your precipitation rates should be matched to your soil type (it's infiltration rate will determine whether or not you create run-off) OR your controller schedule should be modified to accommodate the precip rate and infiltration rate. Netafim does a good job showing the relationship between different soil types, flow rates, and application rates in their catalog. They recommend a 0.26 GPH flow rate for clay soils because the infiltration rate is so slow.

If you're putting down the same amount of water from drip tubing and spray heads, drip tubing is still more efficient than spray heads because less water will be lost to evaporation and drift, as well as more water will reach the plants roots where it can use it. The efficiency leads to less overwatering, which is where the real benefits come in.

To further illustrate the point, some Hunter I20 Rotors and MP Rotator nozzles also have the same precip rates.