Things I Learned: Flood Irrigation!

Yes, that’s right: it’s time to talk about irrigation! WHOO exciting! IRRIGATION YEAH!

Okay, calm down all yous. It may not be the most fascinating topic, but it’s more interesting than you think. And it’s necessary: in places like Paonia, which gets less than 20 inches of rain a year, it’s next to impossible to farm without using irrigation. Zephyros Farm sits below Landsend Peak, which is covered in melting snow. But how does that runoff get to these fields, and what happens to it after that?

Well, I’ll tell you.

Who owns the rain?

The North Fork Valley is almost all agricultural land; decades ago, several major irrigation ditches were dug. The ditches catch snowmelt and watershed from the mountains, carrying that water throughout the valley.

Interestingly, while it’s fine to catch watershed and divert it through your fields, it is illegal to harvest rainwater in Colorado for, say, a small garden. This law is under debate at the moment as more and more urban gardens spring up, but for now, you’d be better off buying water rights to Gunnison River tributaries than setting a rainbarrel under your gutter. Legally, that is.

Landowners get “shares” in one or more ditches, each share entitling them to a certain amount of water use. Each landowner uses their water, and diverts the excess into wastewater ditches… which flow onto other people’s property. Don, for example, owns a few shares in the major irrigation ditches, but those aren’t nearly enough to run a working farm. So he also owns rights to his uphill neighbors’ wastewater. At this time of year, that’s a lot of water.

The oldschool way of moving water through your fields was just to dig small ditches leading from the main source. Where they intersected, SCIENCE! A tarp could be rigged to divert the water in a new direction. This photo does not show a pile of junk in a ditch: this is a functioning water gate made of sticks and plastic!

Making it rain

Thankfully, science marched on, and now we’ve got these big PVC pipes that can be moved easily (much easier than ditch digging) and that are fitted with small gates every three feet. Open the gate: water can come out. Close the gate: water keeps flowing down the pipe.

Zephyros Farm has thousands of feet of water pipe, some of which gets moved around for irrigation, and some of which is buried underground to cover long distances. It’s all set up so that every inch of field can be irrigated, as long as there’s water running down the hill (or flowing from one of the natural springs which supplement Zephyros’ water supply).

Rainflow management

There are two of these water boxes at Zephyros Farm: one for each wastewater source. The water flows through and into the pipes, which can be opened or closed using these valves. You turn the wheel and water starts flowing into your pipe, eventually emerging someplace else (probably wherever you’ve got a broken gate).

To efficiently irrigate 35 acres, the technique is to completely flood each section, so that the soil is soaked to a depth of 3 feet (depth depends on the soil profile). So, you open the valve to send water into the pipe, close all the gates EXCEPT the ones in the section you want to irrigate, and let the water flow.

After each section of field is fully flooded, you move on to the next section. You keep moving around the land, eventually coming full circle and flooding the first section again— and by then, it’ll have dried out and be in need of a soaking.

The fields have furrows which are the same distance apart as the gates, so water will flow as evenly as possible. The water pipe always runs along the high side of the field, and furrows run downhill. And that’s it: water flows through the field, runs into a ditch at the bottom, and on to some other place.

This is actually the neighbor’s field, fyi

Flood irrigation is not a very efficient use of water, but it works— and there aren’t many viable alternatives. Don and Daphne use drip irrigation and other methods when they can, but when it comes to growing hay, this is their best option.

And now you know about flood irrigation, and so do I. Want a bit more background? Try Wikipedia or this USGS educational summary of irrigation.