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Advice on using swales for drainage and dry roots in waterlogged tropics

 
Posts: 5
Location: Sumatra, Indonesia 1800m elevation
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My site is located in the humid tropical highlands on severely degraded land, the original rainforest having been clear cut by a wood pulp company about 10 years ago. The soil that remains is poorly draining clay. We get over 3000mm annual rainfall, with many intense rain events during the monsoon. Large parts of the land are waterlogged for long periods of the year, except the three month dry period (June-August).

Normal practice around here is to dig lots of drainage ditches straight downhill, with vertical sidewalls. Obviously I want to avoid those kinds of ditches, but I also want to plant coffee and fruit trees that can’t tolerate waterlogged roots. Some kind of earthworks will be necessary. Initially I was thinking of planting on mounds, but what Geoff Lawton says about swales for poor draining soils in this video makes a lot of sense. I always though of swales as dryland water harvesting tools, but in this case they would function more as long, narrow drainage ponds and sources of building material for raised ridges.

The site is gently sloped (avg. about 5%), stable clay, and no downhill neighbors, so it should be a safe spot for swales. But while there’s tons of info available on building swales for water collection and infiltration, there’s very little on using them for drainage and keeping roots dry. I’m hoping some people on here might have experience with swales for this purpose and can answer some of my questions.

If I install swales, I’m sure they will fill with standing water for most of the year, if not permanently. Will the berms not get waterlogged? Do I need to compact the swale-facing side of the berm to keep it dry? What effect should I expect in the interswale alleys in this pseudo-chinampa setup?

Normally I would plant agroforestry coffee in lines every 3 meters (with medium trees every 6m and emergent trees every 12m), but that's closer than I’ve ever seen swales spaced. On the other hand, advice about not placing swales too close together is usually focused on maximizing efficiency of rainwater collection, which is not an issue for me. Can you have a denser pattern of smaller swales for this kind of application ?

My site is crossed by several drainage ditches dug by the pulp company when they cleared the land directly above me. If I install swales, would you use them as overflow spillways (perhaps with some erosion control modifications like sloping edges, adding some sediment traps, etc.), or fill them in and start from scratch?

There's lots more to say and ask, but it's getting long for a first post, so I'll leave it here for now. Thanks in advance for any advice.

Some pictures to help form an impression of the site:

Gentle 5% slope down to a wetlands and river, no downhill neighbors. You can also see the thin topsoil and soil horizons in the drainage ditch next to the logging road (my only site access).


Looking directly downslope.


Looking upslope, with old growth rainforest directly next to the site. See if you can spot two people on the logging road for scale of the trees. My site goes to the tree line in the back.


The neighboring rainforest has no waterlogging issues, just beautiful humid leaf mulch. My site was like this less than 10 years ago, making me optimistic that it's not crazy to start an agroforestry system in the current waterlogged conditions.


30cm hole naturally fills with standing water. I expect swales would be filled with water semi-permanently.


Typical example of the drainage ditches that cross my site (although this one is located on a neighboring plot).


The new eucalyptus plantation on clear cut forest directly uphill from me, with a drainage ditch that ends up on my land. If I get an excavator to do earthworks, it will be operated by people who only have experience doing this kind of job, so it would be a challenge to get them to dig the kind of swales I have in mind.
 
pollinator
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Location: NW California, 1500-1800ft,
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I like your thinking and ambitions. I would use woody debris in your berms for the hugelkulture benefits of improved drainage, which is what I use in a temperate and summer dry-winter wet climate with a similar amount of rain all in the winter. I see it as a merging of hugelkulture and chinampas. Best of luck!
 
Bunbunan Situmorang
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Location: Sumatra, Indonesia 1800m elevation
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I want to start a syntropic agroforestry system, so I'd be planting trees that grow very tall on the same berms as the coffee. I was under the impression that hügels are not a good place to plant large trees, have you had success with them?
 
Ben Zumeta
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I don’t remember ever hearing that about avoiding large trees on hugels. What reasoning have you heard for that ? I would make sure drainage and slope is accounted for to keep them from floating the first wet season. Maybe the reason for the no large trees theory is that Sepp Holzer uses the hugels as compost after 15-20yrs? Is it believed that they are not stable enough for large trees? I am not sure what the reasoning is, but I notice that the worlds tallest trees grow largely on their own fallen forebearers, and can live for 2000yrs+ in that manner.
 
Bunbunan Situmorang
Posts: 5
Location: Sumatra, Indonesia 1800m elevation
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Usually the reasoning is that hugelbeds have a tendency to shift and sink as they decompose, and that trees need to root in solid ground for stability. All the hugels I've worked with have been exclusively for annuals and shrubs, so I haven't seen large trees succeed or fail. Searching permies for "planting trees in hugelkultur" gives mixed opinions.

This article stresses that you shouldn't bury the woody debris inside the berm, but I don't think that's what you were suggesting. Rather, build a regular swale with berm, and then a low hugel on top of that for extra drainage, correct?

People in this area doing conventional modern Indonesian-style farming are inadvertently building huge hugel-swales (although usually perpendicular to contour): after the forest is cleared they push all the wood debris to the sides of the fields, next to the drainage ditches. Biomass growth and decomposition is so fast that these piles of wood start becoming solid mounds within a year. These pictures of the same wood debris (from different sides) were taken only 14 months apart:





Unfortunately as you can see they're only used as wind breaks, except for a few tree tomatoes. I've definitely seen larger trees spontaneously grow on these mounds, although farmers cut them down when they start shading the field too much.
 
Ben Zumeta
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Location: NW California, 1500-1800ft,
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I read that article awhile ago, and it is pointing out a key mistake to avoid, but in my opinion it is also making a straw man argument based on the worst possible application of the combination of hugelkulture and swales. Its like saying flight is impossible based on observation of my attempt to build an airplane when I was 9yrs old, planning to have my 5yr old brother fly it first, "cuz he's lighter." It was just poorly conceived, not a proof against concept, and Mr. Spirko's semantic dance around the terminology distracts from the more important point about doing your math and backing up your systems when it comes to earthworks and engineering.

Of course we have to account for 500yr rain events, overflow, and have multiple backup drainage sills! However we need that whether we have wood in the berm or not. Maybe we differ in the definition of hugelkulture, and I would defer to Sepp Holzer, but Mr. Spirko also outlines ways to do what I see as effectively hugelkulture (soil on wood) in the berm of a swale or a terrace in this article and in an online pdc video series. So do Sepp Holzer, Geoff Lawton, and Bill Mollison in the Big Black Book and other publications.  It can be done in multiple ways (wood buried into the hillside like a key, or being placed above the drainage sills' elevation), and the design must be based on climate, watershed placement, soil and other contexts. The basic thing though, is to give water a place to go passively, even in massive flooding beyond any you have experienced, before it can wash out your berm. This is important with or without woody debris in it.

The main, and virtually only time the wood is at risk of floating off, like in the story, is immediately after being built, as it is often built with dry wood. Using dry wood makes it much easier to move, so it is natural to do. However dry wood is like a dry sponge, it will float in a flood. If the wood is waterlogged and spongy from decomposition, surrounded by roots and fungus embedded into the subsoil, and you are not sending a wall of water at it with no place else to go, it will not just float away. This is one reason to water your hugel heavily when building it. Wet the sponge, and in a large enough hugel the wood will never dry out again.

Regarding the settling concern, I am not convinced by any of the arguments I have read, and have yet to see problems relating to that two years into the food forest project down near the coast which I have worked on. Fruit trees generally are better off planted too high than too deep, and exposed root flares are a good thing. Also, as the soil settles, the roots will stabilize the hugel and go into the subsoil to the water table. In our flood prone winters, fruit trees need to be 2-4ft above the water table, which can be a couple inches above the original grade of the once flat site. So I built 3-7ft hugels, starting at grade level with wood, using the crappy soil I excavated from the pathways/driveways. These pathways are far more sinuous than the original straight drainage trench, but they all either grade downstream and/or have a level sill to overflow smoothly downstream at about 1% grade from the input coming of uphill hardscape. One major drainage trench absorbs offsite flows of 150,000+gal/inch of rain (about half of what we get), and is filled with woody debris. This leads into a seasonal pond with a wide level sill leading into pine forest and a stream. The rest of the flow onto the site goes through the path/driveways and down the preexisting drainage trench, which has now been rock armored and provided a cascade where it had once been an eroded incised gully.

I do not want to encourage anyone to do anything that could be catastrophic, and a 1-meter in a day, 1000yr rain event could well make an ass of me, but I think all this needs to be considered in context. Forests grow on fallen forests. Trees fall on steep slopes, creating berms (almost always off contour). Observe how things work in your native ecosystem when undisturbed, and help enable those conditions.

Oh, and don't just take some jackass from half-way around the world's advice without checking it against your own logic and broader research!
 
pollinator
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Location: Boudamasa, Chad
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You have an fantastic set of resources here:
1. Lots of sun in the tropics,
2. Loads of water,
3. Lots of organic material.

The question revolves around the best way to combine these in a productive system. I have dealt with  heavy clay, waterlogged plot of land on a gentle slope in the tropics, so here is what I suggest:

Don't go full on hugel with your swale berms. While some people may be able to design it so that there is no risk of "floating," there are easier ways to use your resources in this context. Particularly, just as mulch. I often lay down a thick layer of wood and branches and just plant into it. Since you are going to grow trees, then this is perfect. Mulch will create deep forest floor soil in short order. In the tropics, this stuff decomposes a whole lot faster than in Austria, where hugelkultur was conceived.

I would dig your swales on contour, as usual, but design meandering water ways from the sill of each swale to the next. So if your swales are, say 25 meters apart, have the sill drain diagonally into the opposite end of the next swale. This will create a bit of flow that will oxygenate your water and keep it from being stagnate. If you really retain water all year 'round in the swales, you could even raise fish. Especially if you're taking drainage water from adjacent land.

So with the large amount of water you're dealing with, I would spread the berm out for the entire width of land between the two swales. This will allow you to do two things: 1, elevate your land a little bit to further reduce water-logging, and 2, allow you to cover the thick layer of woody mulch with a little dirt to hasten the decomposition.

I would also suggest integrating eucalyptus in your system for on-going mulch from chop and drop. Eucalyptus gets a bad rap because people will destroy the land by growing it in mono-culture, but in a forest ecology with abundant water, they are really an amazing resource for both mulch and building material.

I have used all the of techniques I describe here, so if any thing is unclear I'm happy to explain more and share photos. Have fun!
 
Ben Zumeta
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It has also occurred to me, why do you need swales with so much water? I also imagine in the tropics, that water comes more evenly than in my climate (where 90% of rain occurs in winter), but I should ask, what are your longest dry periods, largest rain events, and general seasonal variations in moisture? Here we have large enough rain events (24" in a day back in 1964, 10" day in 2016) and so much deforested and hardscaped land that I would not do true swales (on contour).  I just make the water meander around hugel beds that are almost entirely above the water table, with ponds catching that diverted water on its way. I will also fill any relatively straight standard (desertifying) drainage trenches with woody debris to make the water travel further in contact with biomass.  This was done all the way back in roman times, and evidence from its use back to the Roman age in Britain shows these maintain drainage longer than pipes, gravel or virtually any other method. I think the basic idea is, do not build a half-assed beaver dam where it can wash out and destroy other people's stuff.
 
Bunbunan Situmorang
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Location: Sumatra, Indonesia 1800m elevation
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Thanks for the replies! I don't need swales for dry season water harvesting, and swales are not my first choice solution. I would prefer as little digging as possible, both to save money/time/labor and to reduce the chances of negative effects from major alterations in the land. I just saw that video by Geoff Lawton, and what he claims swales can do in waterlogged clays (abundant surface water combined with well-draining berms) sounds very attractive. I was wondering if anyone here had achieved those results in practice (and if yes, tips on how to replicate their results).

To recap my thought process:
1. The water table is very high, and I don't want to dig deep open trenches for subsurface drainage (the usual solution in Indonesia).
2. Therefore trees will have to be planted above grade, whether on mounds or ridges.
3. The soil for those mounds or ridges will have to come from somewhere. Most efficient would be a ditch right next to them.
4. Some form of runoff control and redirection towards retention/detention ponds is also necessary. If you are digging ditches to build ridges anyway, might as well use the ditches for this purpose.
5. Your end result is a ditch directing runoff flow together with a raised berm for tree planting. Whether this follows contour, a keyline pattern, or a slight downward slope, in a loose sense I think you can call it a "swale".

Particularly, just as mulch. I often lay down a thick layer of wood and branches and just plant into it.


Yes, in syntropic agroforestry a concave raised bed with a thick layer of woody mulch is also the usual practice. But I'm worried in my situation it won't be enough to keep roots above the water table.

So if your swales are, say 25 meters apart, have the sill drain diagonally into the opposite end of the next swale.


I want to plant coffee in much more closely spaced rows, probably every 3 or 4 meters. If swales are placed this far apart, would you plant interswale rows on grade, or build mounds/ridges but without an accompanying ditch?

I would spread the berm out for the entire width of land between the two swales


Basically make terraces? This would require a lot of soil, and deep/wide swales.

Eucalyptus gets a bad rap because people will destroy the land by growing it in mono-culture, but in a forest ecology with abundant water, they are really an amazing resource for both mulch and building material.  


Yes, eucalyptus and banana are the key biomass trees in syntropic systems, and I plan to use them extensively

Here we have large enough rain events (24" in a day back in 1964, 10" day in 2016) and so much deforested and hardscaped land that I would not do true swales (on contour). I just make the water meander around hugel beds that are almost entirely above the water table, with ponds catching that diverted water on its way. I will also fill any relatively straight standard (desertifying) drainage trenches with woody debris to make the water travel further in contact with biomass.



This sounds like a good possible solution with minimalist intervention. Especially like the idea of filling up the existing drainage trenches with woody debris: at the moment they're an erosion disaster, but modifying them would take a lot of work.



 
Nathanael Szobody
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Bunbunan wrote:

Particularly, just as mulch. I often lay down a thick layer of wood and branches and just plant into it.


Yes, in syntropic agroforestry a concave raised bed with a thick layer of woody mulch is also the usual practice. But I'm worried in my situation it won't be enough to keep roots above the water table.

So if your swales are, say 25 meters apart, have the sill drain diagonally into the opposite end of the next swale.


I want to plant coffee in much more closely spaced rows, probably every 3 or 4 meters. If swales are placed this far apart, would you plant interswale rows on grade, or build mounds/ridges but without an accompanying ditch?

I would spread the berm out for the entire width of land between the two swales


Basically make terraces? This would require a lot of soil, and deep/wide swales.



Primarily, I'm encouraged by the photos you posted of the native rain forest: it is not a bog or a swamp. This means that with plenty of organic material you shouldn't need to elevate your trees all that much. My proposal was that you basically scatter the soil between your swales. This would not create a terrace because, as you say, there's not enough dirt for that. It would just fill in a bit your woody mulch to create that nice spongy top soil a little more quickly.

You will become the master of your land and biome through first hand observation. If you need more elevation for your trees, then make smaller trenches with berms in between the swales to plant the trees on. Eventually these trenches will fill in with leaf fall and other detritus--especially if you integrate trees for chop and drop--and create that forest soil you're looking for.

It seems like you have a pretty good grasp of the factors involved; all that's left is to try something!
 
Bunbunan Situmorang
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Turns out some members of my clan took pity on my and offered up their unused plot for me to work with (this is all communal clan land, but plots have been allocated for private use orally). The watertable there is much more manageable, and earthworks aren't a priority anymore. But thanks to this thread I think I'll be burying woody debris under the beds, which I hadn't previously considered for tree planting, so your advice hasn't been wasted. I'll post follow-up questions in the hugelkultur forum.
 
pollinator
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How much land are you working with
I think that you might only need 2acre or 1 hectare for self-sufficiency.  With less land it can be easier to manage.
1 acres fruit/nut trees
0.25 acre mineral dense vegetables and herbs
0.25 acres small fish pond, chicken coop, and honey bee hive, sheep in pens
0.25 acres of calorie dense tubers/grains/beans/etc
0.25 acres for high value market garden produce (garlic, medicinal herbs, herbs, vegetables, eggs, honey, etc

It seems like the plantation above is heaving like a 'roof' and sending all of it's water to your plot thus effectively giving you 3x the avg rainfall amoung, almost creating a swamp.
I would embrace the swamp, I wouldn't drain it instead I would encourage it (to an extent), creating alternating rows(15ft-30ft or 5m-10m) of dry land and then water filled ditch. The dirt from the ditch is dumped onto the dry raw quickly making it high and dry.






 
pollinator
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I'm am replying as a dry land person but a crazy one. I have swales like you describe though my swales are not level and thus drain water away from our driveway and toward a dam area I've been developing. Mine fill and hold water for several days. My berms, made with the dirt from the swales, hold up just fine to that kind of water. I have problems with ground animals in my berms but they are otherwise fine.

I'd absolutely do a small area with really close together swales just like you imagine and see what happens. That's my kind of farming though, the "let's try it and see" kind.
 
elle sagenev
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Bunbunan Situmorang wrote:
This article stresses that you shouldn't bury the woody debris inside the berm, but I don't think that's what you were suggesting. Rather, build a regular swale with berm, and then a low hugel on top of that for extra drainage, correct?



I hadn't heard that.. I buried some wood in my berm and planted a tree on it. I can't report on the success, as the ground squirrels LOVED this and ate my damn tree. The berm looks fine though.
 
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