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Shelterbelts and Windbreaks - A Case Study
   

Overview

Small saplings in a new shelterbelt often need irrigation for the first years until their roots reach deep ground water. Drip irrigation is perfect for starting a shelterbelt or windbreak.

You can use overhead sprinklers but drip irrigation is far more efficient using only 60% of the water. Drip irrigation trickles down to the roots unlike overhead sprinkler water that soaks the surface of the ground and can cause runoff. Drip is not affected by strong winds that can blow sprinkler water away from the saplings.

In the following case study we will design the system to keep the initial costs low. The system will also be scaled small enough to fit the typical water pumping system found on a family farm.

Long rows

Shelterbelt rows are often very long - from 400 feet to 1000 feet. Our shelterbelt is 800 feet long and has five parallel rows of trees and shrubs. The trees are spaced from 3 feet to 12 feet apart in the row depending on the species. Some rows need less water flow than other rows but every row needs a small volume of water pumped over a long distance.

So what size of tubing in the rows will be the most economical? The smallest tubing suitable is 1/2" in diameter such as our T21000 tubing. We could use 3/4" tubing like our T9500 to make the rows twice as long or even 1-1/2" tubing such as our T6600 for very long rows but larger tubing and longer rows will require more pumping capacity and larger diameter mainlines to supply water to the rows. We'll choose 1/2" tubing for its low cost, and ease of installation. It will also keep our water pumping requirements low.

Let's divide our 800 foot long shelterbelt rows into two 400 foot long zones similar to those in the illustration to the right. The main supply tubing from the pump will bisect each 400 foot zone so that each individual row in each zone is 200 feet, half the zone length. That way we can use 1/2" tubing and keep the cost of tubing in each row to a minimum.

The total flow rate for each zone will be in the 400 gallon per hour range, well within the capacity of many farm water pumps. If our farm has a larger pump, we may be able to operate more than one zone at a time.

 

shelterbelt drip irrigation

Drip system plan for a 5-row shelterbelt

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shelterbelt manifold

Manifold design for a shelterbelt or windbreak

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The manifold

We will maintain full pump water pressure in our main supply tubing all the way to the start of each zone. At the start of each zone, we will install a pressure regulator that will reduce the water pressure and will feed the water into a manifold (photo to left) made of 3/4" tubing. From there the water flows through tees and out into the rows.

Row tubing

In our shelterbelt, the trees are small saplings 24" in height. To keep water pumping requirements to a minimum, we'll use a punch to install one D4 dripper next to each sapling along our rows. If our saplings were larger, we may need two or more drippers per tree.

Each D4 dripper will deliver one gallon per hour to each tree. To encourage deep root growth, we want the irrigation to be deep and infrequent. The drip system needs to operate long enough to wet the entire root area. To test to see how deep our irrigation water is reaching, we operate the drip system for an hour then dig a trench close to one of the saplings to expose the soil around the root ball. If we can see that the water has not reached the bottom of the root ball, we know that we will need to to operate the drip system for a longer period each time.

 

   

After we install all the row tubing, we will use mulch to cover the ground to hold the moisture in the soil and to discourage weeds. Tubing in the tree rows is usually left on the surface so that the tubing and drippers can be easily seen and monitored. If we wanted to leave the ground clear to use a mower, we could use OE25 hanging hooks to hang the tubing from a horizontal wire strung between posts.

Pump

The pump for our shelterbelt is located 1100' from the end of the rows so we need to pump a large volume of water a long distance to supply each zone. Our pump must be able to provide 400 to 600 gallons per hour. We will install a 140-mesh FLR5 disc filter at the pump to keep the water clean for our drip system.

Main supply tubing

We need large diameter tubing for the main supply line from the pump to each zone to overcome high friction loss caused by the long distance. In our case, we'll use 1-1/4" tubing or larger so that we could supply enough water to operate the two zones at one time if we choose to upgrade our water pump.

The main supply tubing could be solid white PVC but that type tubing must be buried to block sunlight and to avoid algae growth in the tubing. Black PE water pipe can also be used either buried or left on the surface. In our case, we'll use flat tubing T8300 that is very economical and can be easily rolled up when we want to move the tubing to another location.

 

Row design

Row tubing design for a shelterbelt or windbreak

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trench

Overhead view of gravel filter bed

 

Algae in the water

The source of water for our shelterbelt is a large pond. A pond or any other surface water exposed to the sun will have algae that can clog small orfices in a drip irrigation system. We will install a disc filter that will remove the algae from the water but the filter may need frequent cleaning if we pump straight from the pond. A better solution is to build a gravel filter to remove the algae before it reaches the pump and disc filter.

We will dig a trench from the edge of the water back 30 feet and deep enough to be below the height of the water. Next we install a piece of pierced culvert or other enclosure vertically at the inland end of the trench. We then backfill the trench with coarse rock and gravel and install the pump intake in the enclosure. We'll make sure that the top of the culvert or enclosure is covered so that no sunlight reaches the water. The water from the pond will filter through the gravel bed. Most of the coarse algae will be removed, the filter will need less cleaning and clogging will be less of a problem.

Operation

We'll install a V14 manual valve at each zone to control the flow of water. Zones can be operated one at a time or two or more together depending on our pump capacity and size of our main supply tubing.

We can automate our drip system by adding a timer such as our TM6 battery-powered digital at each zone to replace the manual valve. We then program each timer to operate at a different time of day to avoid overtaxing our pump.

Contact us if we can help determine the most economical size of tubing for your shelterbelt - contact us for details.

 

Winter and Spring

Before frost, we will drain the tubing of all water to avoid damage from expanding ice inside. We will install FC12 tees with OE7 end stops at all low spots. In the fall, we will open the tees to let the water drain. We'll take the filter and pressure regulators inside for the winter. The tubing can be left in place over winter under the snow.

In the spring, we will open the row end stops one at a time to flush sediment from the tubing.

We'll walk along all the rows on a regular schedule to listen and watch for damage to the tubing and drippers.

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