Opening and Closing Irrigation Channels with a Tractor

Irrigation work often starts with a channel: either an open channel that carries water to the field, or a trench in which a drip irrigation main line will be buried. With a spade and pick this job takes days; with the right attachment it comes down to a few hours. But a channel dug at the wrong gradient won’t carry the water, and a pipe buried carelessly in a stony trench will start leaking after a few seasons.

In this guide we cover opening and closing irrigation channels with a tractor from start to finish: identifying the type of channel, planning the route and gradient, choosing the right attachment, digging cleanly, laying the pipe and closing the trench with an auger, and doing all of it safely. In the examples we use the QD35 tracked tractor and its version with excavator arm.

First decide: open channel or pipe trench?

The two jobs look alike, but their priorities are different:

• Open irrigation channel: Carries water on the surface. Here, gradient is everything. Along its whole length, the channel bed must fall at a gradient that keeps the water flowing without scouring the soil. Depth comes second.
• Pipe trench: Dug to bury lines such as a drip irrigation main line or PE pipe. Here the priority is depth and an even, stone-free bed. Because the pipe works under pressure, the gradient is not as critical as in an open channel; even so, a slight fall towards a low point is usually wanted so that the line can be drained.
• Drainage channel: Carries excess water away from the field. Like an open channel, it relies on gradient and should run through the lowest points of the field.

Choosing an attachment before you are clear about which channel you are digging means taking the right machine to the wrong job.

Route planning: gradient, marking out and underground services

Measure the gradient, don’t guess it

The eye is often fooled by the slope of the land. A simple, reliable method is the hose level: fill a clear hose with water and fix its two ends to two stakes. The water at the two ends of the hose always sits at the same height; by measuring the distance from this level down to the ground, you find the difference in level between the two points. Drive in stakes at equal intervals along the route and repeat the measurement.

In an open channel, the right gradient depends on the soil type and the amount of water to be carried. In a channel that is too flat, the water ponds, silt settles and weeds take hold; in one that is too steep, the water scours the bed and the sides. If you are not sure, get help from your agronomist or the district agriculture office.

Marking out

• Mark the route with stakes and string. On long channels, set up a pole at the start and at the end, and keep your eyes on the pole ahead while you drive.
• Decide at the outset which side the excavated soil will go. With an open channel, it can help to leave the soil as a bank on the side you don’t want the water to reach.
• Mark tree roots, piles of stones, concrete debris and road crossings.

Always ask about underground services

Electricity cables, gas pipes and drinking water mains may run under fields and gardens. Before digging, get line information from the relevant electricity, gas and water utilities, and gather information from previous owners and neighbours too. Mark the positions of your own old irrigation lines and drainage pipes as well. If the channel will carry water to a neighbouring plot or draw on a shared water source, discuss this with your neighbours and the relevant authorities beforehand.

Which job, which attachment?

You can see the trencher and trench-closing auger attachments available for the QD35 on the tracked tractor attachments page. If your route has many deep or obstructed sections, the QD35 tracked tractor with excavator arm is worth considering, as it can both dig the trench and till the soil; we covered the pros and cons of this machine in our tracked tractor with excavator arm guide. For deeper, narrower trenches, mini excavator models come into their own.

Digging the channel: step by step

1. Wait for the soil to be in the right condition. In very wet soil the channel sides collapse and the attachment clogs with mud; in very dry, hard soil the attachment struggles and the clods stay large.
2. Make the first pass shallow. The first pass draws the route into the soil and guides the passes that follow. Reach the target depth in a pass or two.
3. Low gear, steady speed. Of the QD35’s 3 forward and 1 reverse gears with high/low range, use the low range. A steady speed keeps the depth and the channel cross-section even.
4. Keep to the line. Drive with your eyes on the pole; small deviations grow over a long channel. If you drift off line, go back and realign that section.
5. Stop at obstacles. Don’t force an attachment that has caught on a large stone or root. Stop the engine and clear the obstacle, or open that section with the digging arm or by hand.
6. Check depth and gradient. Measure the depth every few stakes. In an open channel the best test is the water itself: run a small amount of water into the first section of the channel and watch where it stands still and where it overflows and scours.
7. Clean the bed. In a pipe trench, remove any stones and clods that have fallen to the bottom. The pipe must sit on a level, stone-free bed.

Open channel cross-section and water loss

In an open channel, it is not just the gradient that matters but also the channel’s cross-section. A narrow, steep-sided channel looks neat at first sight, but in loose or sandy soil the walls collapse after a few irrigations and the channel fills with its own soil. Giving the sides a slight slope, in other words digging the channel wider at the top than at the bottom, helps the walls stay up. Clay and firm soils can hold steeper sides; sandy soil needs gentler ones.

The second issue is seepage loss. In sandy and gravelly soil, an open channel can lose a large share of the water into the ground before it even reaches the field. If you see the flow dropping noticeably along a long channel, consider compacting the channel bed, lining the channel or switching to pipe for that section. Which solution pays off depends on the length of the channel and the value of the water.

Laying the pipe and closing with the auger

Once the trench is ready, the real job is to lay the pipe so that it works trouble-free for many years:

• Stone-free bedding: In stony soil, spread fine, stone-free soil under and over the pipe. Sharp stones can crush or puncture the pipe over time.
• A little slack: Plastic pipes expand and contract with temperature. Laying the pipe in the trench with a slight snake rather than pulled tight is generally recommended; follow the manufacturer’s laying instructions.
• Test before closing: Run water through the pipe before closing the trench and check the joints for leaks. A leak found after burial means opening the trench again.
• Backfill in layers: Cover the pipe with fine soil first, then backfill the rest with the trench-closing auger. The auger should push the soil back slowly and spread it out; don’t let large clods and stones drop straight onto the pipe.
• Allow for settlement: Backfilled soil settles over time. Leave a slight mound over the trench and top up any spots that sink after the first irrigations.
• Record the line: Mark the pipe’s route with stakes, photograph it and transfer it to a rough sketch. Years later, this record is invaluable to anyone ploughing or digging in the same field.

Pipe trenches are not the auger’s only job. Closing the temporary irrigation furrows and secondary channels opened during the season once it ends leaves the field level and ready for the next round of tillage. Do the closing while the soil is in the right condition; channel sides that have dried out and hardened strain the auger and leave large clods.

Keeping the pipe below tillage depth stops the plough or rotary tiller catching the line at the next ploughing. You can also take a look at our drainage and pipe-laying guide, where we cover pipe trenches and drainage work in more detail.

Safety: trench edges and the working area

• Keep away from the edge. Don’t run the tracks close to the edge of a freshly dug trench; the weight of the machine can collapse a loose edge.
• Nobody in the trench. While the machine is working, nobody should stand in the trench or within reach of the attachment.
• Don’t go into deep trenches. Deep trenches that people will enter need sloped sides or a shoring system to stop the sides caving in. For this kind of work, assess the conditions together with your health and safety adviser; we cover deep digging and slopes separately in our guide to channel digging with a mini excavator.
• Clear blockages with the engine off. Before clearing roots, wire or stones caught in the trencher or the auger, stop the engine and make sure all rotating parts have come to a complete stop.
• Personal protective equipment: Wear safety boots and gloves, and goggles where needed.

Looking after the channel and the attachment

Over time, open channels silt up, weeds grow along their sides and the water flows more slowly. Cleaning the channels before the irrigation season is easier than battling a water shortage in mid-season. Repair scoured or holed sections at the start of the season; a small breach can send most of the water to the wrong place.

On the attachment side, check the trencher’s cutting parts and the auger’s flights after every job. Bent or worn parts spoil the work and put unnecessary strain on the tractor. Grease the grease points, and at the end of the season clean the attachment and protect bare metal surfaces with a thin film of oil.

Quick checklist

• I’ve decided on the channel type: open channel, pipe trench or drainage.
• I’ve marked the route with stakes and string and measured the gradient with a hose level.
• I’ve got information on underground services from the relevant utilities.
• I’ve chosen the right attachment for the job and left deep and obstructed sections to the digging arm or to hand digging.
• I’ve laid the pipe on a stone-free bed with a little slack and tested it before closing.
• I’ve backfilled the trench in layers, allowed for settlement and recorded where the line runs.

You’ll find the technical specifications of the QD35 tracked tractor, which works with trencher and trench-closing attachments, on its product page. Message us on WhatsApp with the length of your route, your soil type and the target depth, and we’ll work out the right machine and attachment set-up for your job together.