Swale is no longer draining

My swale isn’t draining anymore and is acting like a mini pond. What would cause this? How would I remediate it?

Details:
I installed some swales approximately 40 yards in length in March. All spring and summer we got a lot of rain and they did what they are supposed to and drained once filled. The top swale is still draining properly but the bottom one is just holding water now. Soil composition is clay so not totally surprising but I’m unsure why it has all of the suddenly happened. Bottom swale that’s filling up isn’t getting a lot of sediment. That’s all going to the top of the system. Water is filtering through woodchips on the way through the system.  We last got rain 3 days ago and it’s still full. Swale is approximately 2 foot deep and 4 foot wide.  

Alot of people actual start seeing spring popup all over their land once they install swales. Yes swales are that powerful.

Your swales have been soaking in the water and raising the water table, and now the water table has risen to the swales, If this keeps up you can start planting rice or pecans and even deepen a swale and throw some fish in it. Also ducks for the slugs next year. There is actually a fomula for how many lines of swales and their depth and width. https://www.permaculturereflections.com/swale-calculator/

My recommendation would be to plant alot of daikon radish to help with the clay.

Mine can stay full for 6 weeks or more after pretty significant rainfall.  It's water seeping down the hills.  In non significant rainfall it's empty in a day or 2.

I second what the others are saying, they are working the way we'd hope they would.  

The other thing to keep track of, and be glad you found out now, how long is the bottom swale is holding the water?  It might mean if you dig down in that same zone as the bottom swale you will also find high ground water, which would make it difficult for orchard trees or food/landscape plants that need good drainage won't be able to do well in.   So those sorts of plants need to be higher on your hillside.  Even if this year seems like more rain than usual, every 7-10 years these kinds of heavy rains happen, threatening plants that need good drainage.

Thanks for the replies. I suspect that I haven’t reached the high water table because the swale is on a slope and there is still at least 30 vertical feet and 250 linear feet to the low point at the valley. I haven’t seen any indication on the lower elevation of springs forming which I would expect if we have fully charged the ground water.

We also haven’t had unusually high rain. In fact it’s been lower than it was in the summer when the water drained within 12 hours. The biggest difference is the temperature that has gotten quite cold and is averaging around 32 Fahrenheit 0 Celsius.

I was wondering if it could be that the clay particulates in the soil have sorted themselves into a pattern that makes them more impervious to water. I was thinking about throwing more mulch into the swale to try get some additional bio breakdown to help disrupt the clay if that’s what is happening. Does that sound plausible or should I focus on trying to plant bulrush and other water loving plants into that swale.

Thanks all.

Need a bit more information: how many swales, how far apart are they, and what is the average grade of the land?

Other things aside, it could simply be that the permeable topsoil is deeper at the top of the slope and shallower at the bottom. The impervious and now water laden clay is directing the water downhill and it emerges as a pool. If there was more pressure you’d probably see a spring.

If it’s a steep slope with few trees, be mindful of landslip. In that case you may consider draining it ASAP.

Radhe Webster wrote: I was thinking about throwing more mulch into the swale to try get some additional bio breakdown to help disrupt the clay if that’s what is happening. Does that sound plausible or should I focus on trying to plant bulrush and other water loving plants into that swale.  

I think mulch sounds like a great idea, but then again, I'm one of those people who seems to always think mulch is a good idea. And you could try planting a variety of things: some water-loving plants and some things with taproots like the radish mentioned above, or other deep rooted plants. Some of the variety would probably do well and the others might not, but then you learn from the experience rather than formulating a theory first. Mulch and penetrating roots might help with water infiltration.

It's not inconceivable that somewhere under the soil surface on the slope, there exists a clay barrier, like an sub-soil dam, creating a barrier impermeable to water. This could account for over-saturation on-grade, but no obvious spring formation downhill from you.

Do you know what the geological makeup of your site is? Are you, for instance, sitting atop mostly clay soils sitting in a scooped-out depression of solid bedrock on the slope that might be water impermeable, or at least not easily or quickly permeable?

Did you test your soil?

My other thought accords with yours, Radhe, where the clay is simply holding on to the water because it's mostly clay with nothing to open passages for water and air. I would suggest you try opening those passages.

I would get whatever mineral amendment your land might need in at least two different grades of grit, one coarse, the other fine, like sharp sand, if you can manage it. I would try dusting this into your filled swale (unless it's drained finally, which is better), and if you can get a broadfork in there and fork the mineral grits into the soil, that will open up spaces in the soil that the grit and sharp sand will fall into, holding those cracks open, and giving the clay something other than itself to bind with.

Also, calcium-depleted clay soils can often have permeability or hardening issues. You might want to get gypsum as your mineral grit. If that's the case, adding gypsum might just turn your clods into crumble.

If you already have lots of organic matter in, don't worry about adding more for now. Unless it's sitting in a discrete layer atop your soil in your swale, it's already doing some of the work of increasing drainage, just probably not enough.

The other possible amendment is biochar. It's often not a bad idea, because it houses all the microbiology you want to encourage in healthy soil, and that will draw worms and other larger soil critters, and they will  increase drainage and workability for you.

This is only laterally related to increasing the drainage of your swale, but I would suggest inoculating your mulched areas with aerated compost extract and fungal slurry. This will increase the humus, the mycelia will offer biological connectivity between growing organisms, and will increase the structure of the soil, keeping it from collapsing on worm tunnels and voids that occur in the soil over time, holding the drains open, as it were.

Let us know how it goes, and good luck.

-CK

Any chance that the swale was naturally gleyed (sealed) ? If i am correct with the process layers of algae,  leaves, etc form a water tight barrier. If there's any possibility,  maybe take a stick and punch a lot of holes in it.

wayne fajkus wrote:

Any chance that the swale was naturally gleyed (sealed) ? If i am correct with the process layers of algae,  leaves, etc form a water tight barrier. If there's any possibility,  maybe take a stick and punch a lot of holes in it.

or clay itself? When you disturb soil, erosion will happen in a bit of a uniform manner. With all layers exposed, stones will move a bit further. Sand will be the next, then silt. Clay being the smallest sized one is the most mobile. Wherever water movement slows down significantly, those will have a chance to subside. Clay can form a very thin but totally impermeable layer. Can you broad fork it? Should help.
Edited to add: if that is the case, try not to disturb soil in higher elevations.

That sounds plausible Ayalp. Given the info provided,  it seems to have sealed itself. I remember reading how Sepp Holzer would vibrate a pond, disturbing the ground. Once it resettles, it is as you describe. In layers that seal it. Heavier stuff underneath the finer particles.

Radhe, why is it you want the swale to drain?   I thought the reason for swales was to hold the water back, not let it go downhill off the property.  What's your location?  Are you in summer or winter now?

You might also have a spring somewhere up the hill that hasn't been developed and is flowing underground.

I have heavy clay soil, and a large pond on the side of a hill that is approx. 800 feet uphill from the road below.  It is essentially a large swale, and it has water in it all year long.   It doesn't have a creek input or output, it's just springs contributing to it and seeping out down the hill.   You know, that horrible math problem where if you have this much coming in one side, and this much going out the other, how much is in the container?  The seeping is slower than the entry, and it's a year-round pond.  

We have cattails/reeds and willow trees on the edge and they are a huge amount of work every year.   One whole month is set aside for cutting and hauling them (not every day, but 2 days a week approx.) and it's exhausting sometimes because the weather is hot when the water level is at its lowest.  The willows grow quickly each year and require lots of trimming and hauling, otherwise they grow too big and fall over into the water, which is another huge amount of work to clean that up, requiring a truck pulling out cut chunks of trees.  It is the tradition in this area to build a pond with cattails/reeds, the previous owner did it.  The birds love the reeds, there is an amazing ecosystem at the pond that surprises me every year.  

I love the pond, and I'll do whatever work it requires, but if I had known all this beforehand, I would have simplified things in the beginning.

Cristo Balete wrote:Radhe, why is it you want the swale to drain?   I thought the reason for swales was to hold the water back, not let it go downhill off the property.  What's your location?  Are you in summer or winter now?

I’d like the swale to drain so that it can sink more of the water rather than letting it run off. If that swale is full there isn’t a lower swale (yet) to catch it. It’s going to happen next year but I didn’t have the ability to complete the full project earthworks yet.

I am in Maryland, USA. We are just starting winter but have had a pretty wet year with some very large rain events. All year the swale has filled and drained within 24 hours of filling up. It’s just in the past month that it’s been taking much longer to drain. This last time it was almost 3 days.

The site averages a slope of around 6%. I’ve tried doing daikon in the swale but they didn’t seem to like getting flooded. There are some volunteer black locust loving in the swale and I haven’t disturbed them. I previously did add mulch but a lot of it washed out when the swale filled.

There could be some gleying. I’ll check them once they water has completely gone to verify.

Thanks everyone

This year was the rainiest year on record for Maryland (ie, wettest year since they started tracking rainfall, approximately 130 years ago). That could be your reason.

Chris Spewock wrote:This year was the rainiest year on record for Maryland (ie, wettest year since they started tracking rainfall, approximately 130 years ago). That could be your reason.

Yes it’s sure been wet! Though I’m not complaining too much about it. It’s been great for the fungi!