alternative to swales

Welcome to the forums, Darren. I must admit that I'm not very familiar with your work, yet, but I'm hoping you might expound a bit more on your ideas for swale alternatives.

Thanks for your question Gary and also for reposting too.

The swale has become an almost ubiquitous feature of every permaculture-inspired landscape. I seriously question the notion of using any earthwork-based treatment ahead of considering more passive treatments. I also seriously question the sense in applying treatments that, if one were to apply the appropriate due diligence, are just not necessary.

Following are a number of treatments and scenarios around your question:

1. The water cycle is best restored by having the raindrop intercepted upon impact with the land surface by some kind of ground cover. Plant leaf surfaces are the best surface to encourage as is leaf/plant litter etc. Livestock impact, particularly that of the heavier ungulates, is another means of increasing infiltration.

2. The placement of livestock on a landscape at high density for short periods is well established as being a means by which infiltration can be enhanced. Some people use mechanical soil 'pitters' or 'imprinters', others use the hooves of livestock to do the same thing.

3. Surface cultivation is another means by which you can increase infiltration rates. In humid landscapes it is difficult not to have an array of plants establish themselves on a landscape even after years of continuous cropping. You can accelerate this succession by sowing seeds of your chosing. You can sow these seeds using the Keyline Pattern Cultivation technique, increasing further the interception rates and potential rates of return.

4. Subsoiling is another type of cultivation. When done following contours or especially when done using Keyline Pattern Cultivation (KPC) it radically increases infiltration rates AND like the methods listed above does so across the whole area treated.

Now to look directly at the two treatments (swales and KPC) often compared I have developed the following comparison:

I've calculated the cost of KPC at $0.02/m2 (at $100/hour & 1ha/hour). If you are plowing to say 12"/30cm depth at 1m spacings then that equals approximately 375m3/ha of new air space (calculated at 0.5 x plowed volume) & therefore increased water space in a plowed soil. This is the equivalent of 375,000 litres (97,500 US gallons) of water stored at any given time before gravity/evapotranspiration gets to work. This is equivalent to a 37mm (1.45") rainfall worth of capacity/hectare.

Given the nature of the water cycle and the significant variations of water movement in landscapes due to soil chemistry, biology and physics along with the gravity & evapotranspiration the retention time of this rain (or irrigation for that matter) is going to vary enormously and so therefore difficult to apply a general metric to.

A typical permaculture-type swale (on contour) might be spaced at 20m spacing (@5 x 100m swales/ha) and be 2m wide on the embankment and 2m wide on the cut with 0.5m of depth giving an earthworks fill volume of 1.5m3/m of swale. At 0.5 x fill volume this is 750l/m3 of water or 375m3/ha. The ditch itself is usually not that permeable in a swale (unless its in heavy draining soil types) and so this will hold 1500l/m3 or 750m3/ha of water. In total this is equivalent to 112m3 water/ha or 112mm of rain/ha. At $2/m3 excavation cost this equals $0.75/m2 ($1500/ha) to cover 0.2ha/ha

Now to compare apples with apples:

A swale system that would equal that of the total water volume harvested by the aforementioned KPC would be 165m long and still cost $0.75/m2 ($495/ha) to cover some 0.066ha/ha.

To repeat the KPC costs $0.02/m2 to covers some 0.5ha/ha (@ $100/ha)...

Even after the 3 usual passes we are still way ahead and have covered the whole hectare not just 0.2-0.066/ha + perhaps 30-40cm plus of soil (our results at 'Dehesa Felix' Mills Rd, VIC, AU and other places) and not a permanent incision in Gaia in sight…

At our place 2 year ago we had 75mm (3") rainfall event over 1 hour. This is one of the highest totals we have experienced in the region. We have marine-based Ordovician (485 million years BP) sediments which are class 1-2 dispersivity and quite sodic. Following our treatments using KPC we had zero runoff off of the effected areas. Our neighbours who are set stocked and not managing their soil surface in any way may well have experienced more than 80% runoff during that event – with much of it coming to our place and our dams! All good except for all of their manure and detritus coming our way too as this event effectively scoured clean the soil surface.

This is one of many instances we have experienced where the dramatic increases that KPC has had on radically increasing infiltration rates.

These relatively shallow surface treatments are not a permanent earthwork like a swale or water conservation channels, gradient roads or the like. However they are passive and they are comparitively cheap.

Thanks and all the best,

Darren

Thank you so much for that very thorough breakdown, Darren! I think I will need to read it over a few times before I can understand most of it but I do believe I got the gist. Thanks, again!

thanks for the thorough explanation! it would seem that the advantage of swales is in their relative permanence, while the keyline plowing (i'm assuming yeoman's system?) is more advantageous for cropping? Or would you say that a perennial system established on kpc treated land would be as absorptive as a swaled landscape in the long run (once tree growth precludes more plowing)? ripping the downhill side before the swale is built and even ripping the swale trench itself, potentially, if possible, should lead to a bit higher infiltration rate bumping those swale numbers up a bit, right? Very fascinating calculations.

Corey Schmidt wrote:thanks for the thorough explanation! it would seem that the advantage of swales is in their relative permanence, while the keyline plowing (i'm assuming yeoman's system?) is more advantageous for cropping? Or would you say that a perennial system established on kpc treated land would be as absorptive as a swaled landscape in the long run (once tree growth precludes more plowing)? ripping the downhill side before the swale is built and even ripping the swale trench itself, potentially, if possible, should lead to a bit higher infiltration rate bumping those swale numbers up a bit, right? Very fascinating calculations.

i sort of read it as,
with KPC you should be soaking all available rain into the ground where it lands and have no overland flow.

a swale is designed to stop overland flow and soak it into the ground. in theory, with KPC you wont have any overland flow to catch thus negating a swale.

imo - Darren is saying for the time/cost/effectiveness of the water cycle, the KPC is a more cost way get water into the soil and less permanent than a swale.

hope this helps.

Thanks Kelly, Corey and Gary,

Its all very interesting this stuff — I am a big fan of the book, 'Vegetation and Soils – A World Picture' (Eyre, 1962) as it confirms and expands on what many of us would already suspect — the relationship between the kind of vegetation communities and the behaviour and characteristics of soils as a result.

A simple example is where we have the same ridge — same parent geology, same geomorphology, same agricultural history right up to today. We apply a number different treatments to strips of this ridge. On one we put swales and plant a deciduous forest, on another we do the same only with conifers, on another we KPC and establish perennial pastures, on another we KPC and plant the two forest types and then then others we let nature take its own course. Now lets assume that we managed each of these with best practice — we apply ProSilva principles to the forestry systems and Holistic Management Planned Grazing to the pasture — however did nothing to the natural site.

Lets do this all for 15-20 years. What do you think the soils of these different strips will look like now? How will they behave? Further to this what is the runoff coefficient of each vis a vis the infiltration rate of each? What is the return on investment from each?

Ultimately the ongoing infiltrative effectivness of each of a swale is completely dependent on the management that continues after construction and the chemical/physical characteristics of the soil in the first place. Build your swale out of dispersive clays and it will reach its liquid limit quickly, lose porosity and go to cement when dry. Heavy reactive clays will shrink and swell as they do and water will come and water will go or water will stay sitting for a very long time. And so on it goes.

But yes Corey, KPC between swales is a good idea if it fits with your holistic context.

Cheers, Darren

As someone who grew up in the desert, a place where the San Diego River is a dry wash, when I discovered swales, I was SOLD. The idea of capturing and sequestering waters held a deep fascination. So upon reading this thread it was another cool idea that held merit as well. I googled the term and found an interesting article but more interesting are the comments. The ARTICLE IS HERE.


For me, swales will probably hold sway because most places I am interested are too rocky to run a plow but I like the idea of less labor input and see them both as effective tools in their place.

Okay, highly opinionated and only partially informed comment below:

I've always found this "debate" between swale and KPC a bit dissatisfying. As I have examined both approaches, shouldn't I believe that my goals and objectives married with my particular landscape and its composition should help me choose options for enhancing the landscape and building soil? I've come to the idea that it's not one of the other. But, rather, isn't there appropriate applications for both swale and KPC? As I understand it; however, many are choosing swales when they should be choosing KPC. I'm sure there is a host of reasons for this phenomenon, but it is my observation. Is it an accurate observation? Additionally, shouldn't the element of scale be clearly a part of the discussion? I'm not likely going to KPC a property of 1/2 acre and I'm not likely to build a five-mile-long swale on a 5,000 acre property. The conditions and goals of the owner may call for that big of a swale, but it's not likely that KPC wouldn't achieve the goals of the owner at a better cost/performance ratio. Am I making any sense here?

Dan Grubbs wrote:Okay, highly opinionated and only partially informed comment below:

I've always found this "debate" between swale and KPC a bit dissatisfying. As I have examined both approaches, shouldn't I believe that my goals and objectives married with my particular landscape and its composition should help me choose options for enhancing the landscape and building soil? ... Am I making any sense here?

You are to me, as I said in my post, these ideas are tools. In most of the places I am looking, its too rocky to use a plow for any meaningful distance, but if I had a large acreage of topsoil, I would probably prefer KPC over swales but again, who says you can't use both?

Thanks,

My consistent approach Dan, and you would have seen this quite consistently, is that the first matter to take care of is the establishment of your context and that of your landscape. Secondly another consistent message I've given is that its important to look at all of the means by which an issue might be corrected. Thirdly, and I think this is particularly important, is the treatment you are looking to use addressing the cause or the effect? In many cases swales and other treatments (including KPC) are used to address the effects and don't necessarily address the root causes. For me that is a much deeper question and why I suggest starting with considering and establishing personal/enterprise and landscape contexts ahead of applying money and energy at the outset.

Cheers,

Darren