Plan a Natural Irrigation System

It is easy to move water across the landscape without pipes or hoses. Natural irrigation simply uses gravity. This video tutorial shows us making an irrigation channel on site. Lets dig in and move the conversation beyond swales and trenches.

We used a simple A frame to map out the contours. Yes, you can buy equipment to do this, but A frames can be made with very little expense. And when you use the A frame regularly you get good at it.

You also get a feel for the slope and have a visual estimation of what you think each contour line should look like. Rowena explained how she saw how the contour hugged the landscape. “Well, I’ve just gotten down low, closer to the the ground so that I can visualize it. I’m visualizing the slope of the land and where the water is running and perhaps where we could capture it. It feels like it’s wrapping around um at the base of a hill.

Moving the topic of swales, trenches and channels along

In previous tutorials I have explained the difference between a trench a ditch. And how a swale is a similar to a ditch that sits perfectly on the contour. It catches water and it allows it to seep deeper into the soil.

On the other hand, a keyline irrigation channel can look almost the same but it it’s used to move the water slowly out from the wetter areas to the drier areas. So, the swale a trench a bit like a long bucket with holes in it we don’t have any plastic lining in it we need to be really precise because the swale sits level on the Contour it catches the water and it allows it to seep through the soil. Sometimes I check if the swale is level and not leaking by filling it with water or checking it on raining days.

Grant Lubyckij testing then re-digging the swales to create irrigation channels at Gillys Kitchen Garden in Otford
Grant Lubyckij testing then re-digging the swales to create irrigation channels

Check and Plug Leakage Points

Rainy days are perfect for checking for leakage points. Sometimes I check if the swale is level by filling it with water or checking it on raining days. Digging a channel requires a little bit of preparation. You don’t just mark the contours. You need to do the mathematics and mark a fall from that contour. [I’ll show you how to do that]. But the good news is that extra bit of preparation means that the irrigation is self-cleaning. This is because as the surface water moves along, it washes out loose debris.

Comparison of Swales and Irrigation channels

Swales hold the water but channels move water from wet gullies to dry ridges. This is a small part of the key line a method that was pioneered by PA Yeomans Snr during the 1950s. His method has rehabilitated many large farms around the world. At the end of the video I showed ways to apply this gravity fed irrigation system to regenerate a site.

Two Ways to Move Water in a Channel

The two ways to use gravity to move water across the landscape are: 1. having the trench with a slightly downhill direction and 2. Digging deeper to get to where you want to go. Grant Lubyckij is re-digging the swales here at Gilly’s Kitchen Garden in Otford. One area of the garden was always dry. We plugged up the leakage point on that garden and Grant re-dug the swale deeper to convert it into a channel and get the water to move in the opposite direction.

Exercise Your Mathematics Mind

Simplified Mathematics for Channel Irrigation

Imagine you’ve walked across the slope of a hill when you walk across the contour. One foot is slightly lower than the other. But, we’re feeling pretty balanced. Whereas, when you walk uphill you can feel pressure in the heel of your boots. And when you walk downhill you’ll feel pressure on the soles of your feet.

A Steep Slope

When we drop downhill by 1 m in height for every meter that we’ve gone across the slope we’re walking down a steep path. Most landscape standards call this a slippery slope and you would be advised to install hand rails, retaining walls and steps prevents people falling.

A 1/3 Slope

Now, let’s imagine you’re walking across open fields going downhill as you walk. You’re walking across a slope but you go down only 2/3 of a meter instead of the whole meter. It still feels like a slope but by landscaping standards it doesn’t require steps or a retaining wall that’s called the 1/3 drop. This is a slope of 30°.

The Goldilocks Slope 15°

We all know that the easiest way to get down a steep hill in a very open space is to go slightly downhill as we travel across. Now imagine you drop downhill by only a third of a meter or yard for every meter that you walk across. This gets us the magical 15° off contour. You feel like you are gently gliding.

This gentle slope is sufficient to enable rain water to travel along without causing erosion.

Overcoming Obstacles

If you find that there are trees or rocks in your way you might need to do a combination of deeper digging and going off contour.

keyline channels and bare garden beds
Grant and Tim market garden

Grant and Tim have now developed a productive market farm using these natural irrigation technique skills.

When we work with nature, we are giving nature a chance to recover and repair.

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