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Macro Effects of Swales on Watershed

 
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Location: Howard County, Maryland
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Permies,

I've got more of an academic question for you.

When doing permaculture on a property, having observed the property and developed a design, earthworks are a good candidate for step 1 in the transformation. Permies know that water is the key to life and that spreading, slowing, and sinking water where we want it is a good thing. We talk about how this is a win-win for the land we steward and downstream lakes and bays, who now get less of our topsoil, not to mention less nitrogen runoff from downstream neighbors who fertilize their beautiful lawns. We take water that might quickly move downhill on the surface and slow it to put it in the soil.

My question is thinking about this from the macro perspective. Is it good for everybody to do this on the land they steward? Are there any negative impacts if this particular activity (digging swales to maximize water in the soil) when done on large scale? What are the effects when thinking about this phenomenon on areas of scale, say, a watershed? Is it possible that there is too much of a good thing in this matter? What would that look like? How would we recognize it?

 
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Location: Portlandish, Oregon
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I am inclined to believe it is good for everybody. Here is my main reason. A long time ago before my breed of humans came here from europe, there was a shit ton of beavers making ponds. Everywhere the setters found beavers there was fertility. As the beavers were killed for pelts and things, fertility in those areas began to drop with the water tables. It is my belief that it is now our responsibility to do the beavers job, since we removed them.
 
gardener
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I would say it really depends on what it is you're using to measure 'good'. While rehydrating landscapes is a great thing some of the consequences may feel not-so-great to people that have to deal with it.

One of the main things that come to mind is the talk of getting springs to pop up lower in the watershed. That's a great thing unless you're the guy who's house is where that spring started coming up. Truly rehydrating the landscape on a large scale will cause changes and those changes will affects some things negatively.
 
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I think over all the effect will be beneficial except for the possibility of inconvenient springs which some people might have to deal with. But those are much less problematic than the catastrophic flooding alternating with water shortages that we currently have.

 
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I would go with a "it depends" on this one. I don't think swales are going to be the right solution for every situation or climate. There is more than one way to slow, spread, and soak water on a landscape and that should always be factored into the equation. Swales can create frost pockets and all the problems that go with that in cold climates so maybe a hugelkulture would be more appropriate in that case. Something like that would definitely not have the same broad scale results as swales, but might have similar results in mitigating catastrophic hydrologic events.

There's a ton of different metrics for determining 'good' vs. 'bad'. I think this is where the idea of a thousand different "artisans is seed and soil" comes into play. Diversity is king here and there's always another way to skin that cat. Different stewards should be coming up with different solutions to problems they encounter, so the likelihood of massive, singular solutions would not be probable.
 
Tyler Ludens
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For information about a diversity of rain harvesting structures, I recommend "Rainwater Harvesting for Drylands Volume 2" by Brad Lancaster. Also a lot of info on his website: http://www.harvestingrainwater.com/
 
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If the property upslope from me put in swales that caused a spring to pop up on my property in an inconvenient place, I'd move whatever was being inconvenienced.

Because that's a spring! I now have a spring!!!

Springs rule.
 
Tyler Ludens
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My goal is to have springs popping out all over our place. That would be keen! Because of the topography, nothing we do here will have a negative effect on downstream neighbors.
 
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I think it's OK if swales are stable and do not cause soil erosion.
 
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Mosquito breeding and fungal disease both come to mind. My swale has been full for 3 months. Same thing happened last year. While the fungal disease may have happened regardless, the mosquitos are a direct result of the swales.

But... with the swales come frogs, then tadpoles, then more frogs. They may be keeping the skeeters in check.
 
Tyler Ludens
master pollinator
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Yeah, I'm not sure how we can have small bodies of water without mosquitoes. Here, hollow trees collect water (we call them Magic Trees) which harbor mosquitoes, frogs, etc.

I think having a robust ecosystem is about the best we can do about mosquitoes, plus screens or mosquito netting in the house.
 
Jason Silberschneider
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wayne fajkus wrote:Mosquito breeding and fungal disease both come to mind. My swale has been full for 3 months. Same thing happened last year. While the fungal disease may have happened regardless, the mosquitos are a direct result of the swales.

But... with the swales come frogs, then tadpoles, then more frogs. They may be keeping the skeeters in check.



Errmm... swales should hold water for a few minutes tops before the water soaks into the ground. What you have sounds more like ponds or dams.
 
Posts: 37
Location: San Francisco/Gualala, Ca (zone 8)
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wayne fajkus wrote:Mosquito breeding and fungal disease both come to mind. My swale has been full for 3 months. Same thing happened last year. While the fungal disease may have happened regardless, the mosquitos are a direct result of the swales.

But... with the swales come frogs, then tadpoles, then more frogs. They may be keeping the skeeters in check.



If I could hold water for 3 months, I'd be thinking 1 thing: Chinampas!
 
wayne fajkus
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Jason, if it rains for 6 weeks it's gonna be full for 6 weeks.

Ryan. Ditto. Not in the swale but I got a low spot that is still marshy today even when the swales are dry. Been watching some videos. Excited about prepping a chinampa.
 
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The effects of swales and other earthworks on a watershed depend mainly on local climate and local circumstances. If your climate is dry you obviously want to capture and infiltrate as much water as possible. In a wet climate I think erosion control is the main thing.

Swales and other earthworks can be adapted to your circumstances and preferences. You can also include effects on the watershed in how you decide to adapt them.

To give some examples based on comments above. Say your climate is so wet that your swales remain filled for a long time. This could point out that your ground water level is close to the surface. Infiltrating water is not your main priority then, but erosion control probably is. You want to slow the water flow and probably also delay the water flowing downhill. You can then modify your swale by for example:
- lower the overflow so less water remains in the swale after it stops raining.
- make the overflow at the bottom level of the swale, but fill the overflow with rocks. Water will still back up in the swale because the rock dam won't let all the water pass at once, but you limit erosion.
- use brush dams instead of swales.
In the examples above, please do calculate your maximum rain event water amounts so you do understand how much water has to pass through the overflow. Make sure it's big (wide) enough to avoid creating erosion at the overflow.

Areas where the groundwater level is high are indeed great for ponds (just dig a hole, it will fill up and you don't need to compact the bottom either) or chinampas. But you could also maybe dig a diversion swale bringing that water to a dryer area. It all depends on your terrain of course.

In case water does not properly sink into the ground because your swale bottom is compacted, try adding wood chips or other organic materials inside the swale. When they break down our microscopic allies also improve the structure of the ground which increases the infiltration of water over time.

What I hope to make clear is define what you want, observe what happens when you make changes and be creative with changing things again if needed. There are a lot of variations you can make.

 
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