Advice on putting swales into a food forest

Hi all,

I want to turn a mango orchard into a food forest and I have started to plant fruit trees combined with a bunch of native NFT and flower trees.

It becomes very dry here - already now, just after the rainy season has ended - and I realise the enormous work of watering (keeping alive) all of the new baby trees.
So I thought it would make sense to dig some swales and try to keep the water as long as possible on the property. I have an irrigation channel running at the top (North) that occasionally will have water. I could re-direct some of the irrigation water into the swales from time to time during the dry season.

My initially idea is to dig relative small swales, maybe 1 feet wide and 1/2 feet deep. Each swale could have an overflow that would lead water down to the next swale and eventually end up in the lowest irrigation channel that runs out of the property (and to a river about 350 meters away).

Downslope from the food forest is a small rice paddy.

I have sketched out my idea on the attached image. Blue lines are existing irrigation channels, red lines indicate length, purple lines are the swales I imagine to dig - however, I don't know the number of size of them yet. That's what I hope to get some input from you on.

I have also attached a elevation map.

Could this work? What would be good width and depth of the swales? Anything else I could think of before I start to dig? Any risks on having swales on the property like this?

Also - ideally the trees would be planted on the berm, but that's too late now..

Thanks, Mark

Mark Hansen wrote:
.... and flower trees.

what human edibles do the flower trees produce?

Mark Hansen wrote:
It becomes very dry here - already now, just after the rainy season has ended - and I realise the enormous work of watering (keeping alive) all of the new baby trees.

You might want to calculate how much water you get during the monsoons (alot isn't a useful quantification).  On every 3mx3m of land you have, 16.4 milliliters of rain will give you 235liters of water if you  catch it all. If you catch it all, you'll easily be able to water your food forests in the very dry season.  Find the flowing water that comes on to your property during the monsoons at the highest point of your property and dig a very deep and narrow pond (lower evap rates). Make this one 20,000 liters if you don't know how many liters flow into your property from above during the monsoon season.

Find where the water leaves your property in the monsoons and dig a very deep pond narrow pond there. Do the calculation I mentioned above to determine how much water your land gets during the monsoon for your entire property and make it that size (probably more than 40,000 liters).  

After you've dug the ponds and the connecting swales from one pond to the other, watch the first monsoon so see if your highest pond over fills well before the monsoons are over...if it over fills before the monsoon is half over, you need to dig it deeper during the dry season.  If it over fills the very first rain of the monsoon, it needs to be much deeper, maybe 100,000 liters.

Mark Hansen wrote:
So I thought it would make sense to dig some swales and try to keep the water as long as possible on the property. I have an irrigation channel running at the top (North) that occasionally will have water. I could re-direct some of the irrigation water into the swales from time to time during the dry season.

Where is north on your images?  Where is East on your images?

Mark Hansen wrote:
My initially idea is to dig relative small swales, maybe 1 feet wide and 1/2 feet deep. Each swale could have an overflow that would lead water down to the next swale and eventually end up in the lowest irrigation channel that runs out of the property (and to a river about 350 meters away).

Those swales sizes won't do much at all in holding water, they will direct water but not hold water. 1 meter wide (about 3feet), 2 meters deep. dig the swale extra deep (more than 2 meters) for placing logs, and twigs and leaves which aren't poisonous to other trees/plants and then bury these in the bottom so you retain water in the bottom of your swale.  Do the same thing on the berm side of the swale: bury logs, branches, twigs which aren't poisionus to other trees/plants, and bury those inside the berm so your berm retains water.

Mark Hansen wrote:
I have also attached a elevation map.

I see the colored line sketch, I see the thermal image but I do not see the elevation map.....do you have an elevation map?

Mark Hansen wrote:
Also - ideally the trees would be planted on the berm, but that's too late now..

No it isn't to late. your swales can be bermed along the tree lines if the elevation map shows that this is possible.....just make sure your trees aren't a species that  won't die if you bury two meters of their trunk.
Then, where spacing allows, place seedlings or seeds on the berms

Orin Raichart wrote:
what human edibles do the flower trees produce?

I didn't planted the pure flower trees for edibles. I wanted to have a mix of fruit trees, natives trees and other beneficial trees.

E.g. I have planted humming bird tree (Sesbanian grandiflora) which is a fast growing NFT and use the flowers in omelets and stir-frys. I can also eat the leaves. I have planted "hog plum" (Spondias mombin) because it should be able to live close to the bamboo and use the leaves in salads and stirfries.

Orin Raichart wrote:
You might want to calculate how much water you get during the monsoons (alot isn't a useful quantification).  On every 3mx3m of land you have, 16.4 milliliters of rain will give you 235liters of water if you  catch it all. If you catch it all, you'll easily be able to water your food forests in the very dry season.  Find the flowing water that comes on to your property during the monsoons at the highest point of your property and dig a very deep and narrow pond (lower evap rates). Make this one 20,000 liters if you don't know how many liters flow into your property from above during the monsoon season.

I did write down the amount of rain per week and month during the rainy season, so I have a pretty good idea. I have a pond on top of the property (400 m2 / 4300 ft2, 2 meters deep) that will be fed from irrigation channels throughout the dry season. I also harvest rainwater in two 65.000 liter tanks. So hopefully I have water enough.

I won't be able to dig a lower pond big enough to hold all the water that falls on the property during rainy season. I did actually just dig a small pond (see other post I made) but it won't hold a lot of water. The main reason for thinking about swales is that the "food forest" is very dry in areas and when it rains then the water just run off down to the rice field and eventually out in the river (after passing a few more farms).  I would like to retain the water longer and have it seep down into the ground in hope that the trees will access it during dry season.

Orin Raichart wrote:
Where is north on your images?  Where is East on your images?

North is straight up, East is to the right.

Orin Raichart wrote:
Those swales sizes won't do much at all in holding water, they will direct water but not hold water. 1 meter wide (about 3feet), 2 meters deep. dig the swale extra deep (more than 2 meters) for placing logs, and twigs and leaves which aren't poisonous to other trees/plants and then bury these in the bottom so you retain water in the bottom of your swale.  Do the same thing on the berm side of the swale: bury logs, branches, twigs which aren't poisionus to other trees/plants, and bury those inside the berm so your berm retains water.

Ah, I was hoping that smaller swales would allow for *some* water to be held?

Orin Raichart wrote:
I see the colored line sketch, I see the thermal image but I do not see the elevation map.....do you have an elevation map?

Yes, that is an elevation map. It goes from Red->Yellow->Green->light blue->dark blue, with red as the tallest features and dark blue as the lowest features.

Orin Raichart wrote:
No it isn't to late. your swales can be bermed along the tree lines if the elevation map shows that this is possible.....just make sure your trees aren't a species that  won't die if you bury two meters of their trunk.
Then, where spacing allows, place seedlings or seeds on the berms

Ok, noted.

Having 2 meter wide swales would be a drastic impact on the garden - I was hoping that smaller would make a difference too.

Thank you for your input!

Hi Mark,

As always in Permaculture every answer depends on local circumstances and the desired results.

For swale sizes and the distance between swales it's a rule of thumb to work with the maximum recorded 24 hrs rainfall in your area as a guideline. Then you need to know the catchment area above your swales. That's basically all the terrain above your property that sends water your way.

These numbers will tell you how much water to expect in a once in 10 years (or longer) extreme rain event. This is a good number to know anyway, even if you don't dig swales, because it will tell you how much water might pass over your property in a big storm. I believe it's always wise to make sure excess water can pass without creating too much damage. Swales and ponds or not, this water might come at you one day and it's best to be prepared for it.

For swale sizes and distances between them you could use this online calculator: https://www.permaculturereflections.com/swale-calculator/
Please do read the explanations and even the comments, they're helpful!

Swales are one way to improve water retention. Others are keyline plowing, or terraces. If you have gullies on your land checkdams might help.