Spray Irrigation

[SkinnyDip]

We have a small MBR WWTP and instead of drip irrigation I was told to do spray irrigation over a grassed area. I don't have any experience in the design of spray irrigation. Rain Bird was not helpful. I found specs on some of their pop-up heads and found something I thought was reasonable. 15' radius spray with 30psi. It will be over 1.14 acres. I figured layout of the heads and pipe sizing would be easy enough using EPANET and an emitter coeff of 0.7. So now I need to find a pump capable of delivering the flow to each zone and maintaining 30 psi. Now the questions start. Should I just use something like a Myers centrifugal pump or is there a different style better for this set up? What other fixtures are needed with the pump such as pressure regulators or dampeners or things of that nature. Another question. I was told the application rate was 0.8 gal/day/ft^2. Which is 1.28"/day. The sprinkler heads are capable of delivering this in less than an hour. Does the sprinkler need to be operated for 5 min. several times per day to prevent runoff? I know this is a confusing question but drip irrigation makes much more sense for infiltration. Any help would be greatly appreciated.

 

[atook]

For an area this small, you can probably let the installation contractor come up with a design for you, or an even an irrigation engineer..

For the pop-up sprays, create a supply that provides 50GPM at 50 PSI.

If your areas are larger than 20' across however, I would recommend going to rotary sprinklers instead of sprays, you'll find this more cost effective. You'll need more pressure for these heads, plan on 50 PSI at the heads, give yourself a supply of 70 PSI.

If you're going to be using effluent water for irrigation, that's another reason to go with the rotary sprinklers, as they don't clog as easily as the sprays.

Your daily application sounds very high. Here in Colorado/Wyoming, I typically plan on applying .31 inches/day, which typically gives pop up spray sprinklers a run time of less than 10 minutes per day.

Tim Grote - The Irrigation Engineers.

http://www.irrigationengineers.com

 

[bimr]

Metcalf & Eddy's Wastewater Engineering has design informatin for spray irrigations systems.

I would doubt that drip irrigation would work since the nozzles would clog. Even if the water was solids free, you would probably get some biological growth and or scaling that would clog the drip nozzles.

In addition, you should be careful where this is applied. There are many areas of the US particularly in the North where such a system would not work or you would have to incorporate so much land that the system is impractical.

One such application that I have visited was installed as part of a "zero discharge" aluminum rolling mill in Tennessee. The soil was a hard pan type clay material with low water absorption capacity. As originally designed, the spray irrigation system would not work. The operator moved his spray nozzle around the site until he found an sinkhole that would take the water. Of course, that solution was illegal.

 

[SkinnyDip]

Thanks. We are in the coastal region with good sandy soil that will take quite a bit of infil. We have done these systems before with drip irrigation and all still work good. I think we can apply a lot of water but I want it at a relatively low rate so we don't have runoff. I am now thinking of going with rotary sprayers so it applies only 0.5"/hr. This way under maximum load they will run for 2.5 hours per day. I assume it will be broken into several applications to prevent runoff. Atook, you mentioned a very high flow system. I am no irrigation engineer, but that seems like it would be less efficient since we are trying to get rid of the water, not conserve. Am I too far off base?

 

[atook]

Skinny Dip:

If you're trying to get rid of water instead of conserve it, then you're right, you'll want to over apply.

I created a similar system to distribute WW at a jail here in Colorado. Local agencies did not allow us to over apply for fear of contaminating the ground water, so we used a central control system hooked up to a weather station that calculated the applicable amount daily. We also incorporated moisture sensors to stop irrigation if we saturated soil below the root zone. We even had the system shut down if the wind blew too hard. If I recall correctly, the jail actually baled and sold the alfalfa crop derived from the process.

If you're running effluent water, I'd use a larger rotor (60'+) radius or even consider using an impact rotary sprinkler (less moving parts) as we used in the above system. Note that Rainbird and Hunter manufacture irrigation equipment for re-use water that includes scrubbers in valves, etc.

Tim Grote - The Irrigation Engineers.

http://www.irrigationengineers.com

 

[SkinnyDip]

Thanks atook. I wanted to use large rotors but am worried about bad wind drift since it is in somewhat of a residential area. Also, our areas of application are small and square/rectangular and I figured smaller radius would allow more efficient coverage. I also figured on just a basic precip gauge. I guess it will all depend on what the state allows/requires. By the way, our effluent will be treated to very high quality. Much better than any nearby receiving streams. But still not allowed to directly discharge. So I take it I am halfway on the right path? Thanks for ya'lls help. If ya'll think of any more advise I'm all ears.