This is a link to Google Maps that points to an area near the town of Liberal Oklahoma, and it’s got a series of circular fields. They look weird. What’s the deal?
It’s circular irrigation. The field is irrigated by a long arm on wheels that pivots around its central point thus producing a round field.
Oh. They look like enormous circles, they must be big pieces of machinery.
They can be hundreds of metres long.
Check this link.
They’re certainly not confined to Oklahoma as you’ll see them while flying over much of the southwestern US, especially in areas like Colorado’s San Luis Valley. My guess would be these areas represent artesian aquifers instead of a surface water supply. A casual observation would suggest they pivot around a well source and the water travels down a central tube that rotates like a clock arm, probaby driven by the water itself. Periodic tall wheeled tripods keep the tube at a consistent elevation. Since the outer perimeter is travelling faster than the inner, another assumption is that the sprinklers are calibrated so that more is respectively discharged toward the end.
I just asked a qustion about this last week. This method of irrrigation is called center-pivot irrigation. The only thing I was never able to figure out exactly is how the whole thing keeps itself straight.
Blimp Pilot: You see the circular patterns on those fields? That’s from centre-pivot irrigation.
Homer: [impressed] Wow.
Blimp Pilot: Now let’s see what’s going on at the Super Bowl.
Again, just a guess but I’d figured there were water drive mechanism at each of the wheeled supports and that some care was given to insure proper gearing of these so that the outer fringe would keep up with the inner. Also, it would appear that they each follow a circular path that undoubtably has been made level and free of obstructions.
“Made level”? I guess you’ve never been to West Texas or Oklahoma. It would be a major undertaking to level a field that size, but fortunately nature has taken care of that for the farmers.
I remember being in my early 20s, on an airplane, and the pilot announced to the passengers that the circles were central pivot irrigation fields. I thought to myself “Duh! I suppose he’s going to tell us next that those little things travelling on the road are called ‘cars’ and they have four wheels and carry people where they want to go.” It had not yet crossed my mind that there were areas of the country that were not covered in these circles.
Mostly bipods, I think. Check out Ithaka’s link.
Thanks RM, I meant a wheeled triangular support but your “bipod” is more accurate.
As a geologist who’s lived in the region for around 38 years, yeah, I’d kinda noticed what passes for relief. Still, I’m rather skeptical that a farmer could just assemble the rig, turn it on and expect it to maintain a straight, unkinked operation. Driving by, as you look down the paths it’s apparent some work has gone into creating a more level, smooth, circular plane of operation for the wheeled supports than the surrounding topography. You don’t have to “level a field”, all he had to provide is efficient concentric rings because very little of the apparatus actually touches the ground.
So what happens to all the land between the circles? Does it just go to waste? Is that where farmboys have their keggers?
On my last cross-country flight a couple of weeks ago I saw a center pivot field (in Oklahoma or Colorado, or maybe southern Kansas) being burned, presumably on purpose.
It was quite the sight to see from 30,000 feet, a big “prairie fire” contained nicely in a circle.
I’ve seen these on flight before, and had also always wondered about them. I kinda put the irrigation story together myself… (yay for inductive reasoning!)
However, I don’t necessarily get the missing sectors in these fields. You see various angles dividing green from brown. Sometimes a thin sliver is all that’s missing, sometimes it’s morel ike half. The Google Maps picture linked to tin the OP shows a decent variety of these Pac Man shapes.
What’s that all about? Obstructions? Aiming for a particular acreage of alfalfa?
The ones I’ve worked with use an electric drive. They’re calibrated to keep themselves in line.
There’s a liberal part of Oklahoma? 
The slices are either for a different crop, or for an unplanted area. The flow of water can be adjusted as an irrigation arm passes over an area. Most pivots cover an area of about a quarter square mile (5,473,749 square feet, to be more exact.) If a farm covers two square miles, that means a farmer will have eight pivots. They might want to experiment with a new crop or hybrid, and the only way to accomodate it would be to plant it in a slice, so watering is unofirm for that crop, and it doesn’t affect other crops that might have different watering requirements.
The pivots aren’t limited to rotating in one direction. A farmer with a rectangular 1/8 acre plot (2640’ X 1320’) can use a full size irrigation arm, reversing it after it reaches 180 degrees from the point of origin.
The fields around here need no prepartion prior to assembling the center pivots (they are very common here, Texas Panhandle). The fields still have to be plowed and such, there is no consideration given to leaving paths for the wheels to follow. The irrigation assemblies are pretty flexible, they will follow the terrain even if it’s not perfectly flat.
The speed of rotation is set with the furthest wheel set from the center, switches are used to maintain alignment for the inboard drive sets. If the wheel set is lagging, it’s switch remains closed for a longer period, allowing it to catch up.
You do with the unirrigated corners whatever you’d do with any other unirrigated land. In some places I expect that means it’s essentially useless. Up here it will just get seeded to a different crop, but I can’t tell you about Oklahoma.
If you zoom in on the map, you can see that most of the large chunks are due to the irrigated circle being cut into two or more fields. The satellite photo looks like it was taken shortly after harvest. Some fields are the golden brown of straw, and other look like they’ve been recently tilled. Barring major physical obstructions, you’ll keep any land under a pivot in crop as much as possible, since those things are rather expensive. If you zoom in on the little slivers, you’ll see most of them contain a farmyard or other similar obstruction.
Right you are… The lateral pipe is supported about 3 meters above the ground by a truss network, spanning towers approximately 45 meters to 50 meters apart. Each tower is an “A’” frame driven by a small electric motor of 1hp or 1.5 hp. The lateral pipes are typically 6 5/8", 8", or 10" in diameter.
Duke, I’d imagine that’s going to vary from place to place. Those in your locale are most fortunate.