Swaling for sandy soil

[ottawagardener]

Not sure if this is the correct section but here goes:

The top part of my property is well drained sandy soil. The bottom is clay. Anyhow, it is on a slight westerly slope and I am anxious to irrigate as little as possible. My usual techniques including mulching, letting plants that root along the stem sprawl and farther spacing along with incorporating uncomposted organic matter nearby and planting moisture-cool loving planting in hollows rather than hills.

I'm also digging swales across the 'old' garden/orchard. I'm not planting disease prone crops here because the garden had been used for decades and is a bit infested I presume. It also has a small orchard so I'm underplanting with a diverse mix of semi wild plants and perennials instead.

The swales run along the topography 'terrace' style but there is also a path that cuts directly through. It follows the direction of runoff. I am not sure what to do with it. Should I dig it out and mulch it? Should I plant it with a green ground cover to capture water though this would also use water. Should I carve it to direct the remaining flow (slightly higher than the swales) down toward a small irrigation pond as just past the end the clay begins? I think I'd like the pond. What do you all think?

[Joseph Lofthouse]

At my place any extra runoff is directed towards the terraces. Any runoff from the terraces is directed towards a catch-basin. I figure that the longer I can keep the water higher up on the farm the better. Any water that soaks into the ground at the top of the hill is more likely to water the entire hill as it slowly seeps down to the bottom.

[raymondo]

A path that cuts through would surely defeat the purpose somewhat. I have sticky clay, rock hard in dry weather. I put swales in to slow the water down when we get torrential downpours, a regular feature of our summer rain. I'm with Joseph. Keep the water in the high places as long as possible.

[ottawagardener]

The path that cuts through it was there before for access. So should I put a pond in the bottom to collect the additional rain fall? I should post pictures soon. Or I could remove it all together I suppose.

I have another garden higher up with swales and nothing cutting across it. It's in an even drier place so here's hoping.

[stone]

Apr 15, 2011 7:25:33 GMT -5 ottawagardener said:

The path that cuts through it was there before for access. So should I put a pond in the bottom to collect the additional rain fall? I should post pictures soon. Or I could remove it all together I suppose.

What did you end up doing?

There is an obvious (to me) tack of keeping the path, and simply mounding up the swale over the path... that way, you have both. Yeah, driving over the swale means a bit of roughness, but... it's the farm, it isn't supposed to be a highway.
If you allow the water to wash down the path, you have erosion... a much worse problem.

[traab]

It will be interesting to see photos of this garden to understand the slope.
Some of my garden is light glacial windblown sand/silt. It is easy to work but overlies gravel and stone. I enjoy seasonal digging and dig trenches about 0.5m or wider digging off the topsoil layer. I fill this trench with all garden remains instead of removing plant material to the field edge as others do. The topsoil is interspersed as it fills and tops off the ridge. With rough material buried long root crops are planted elsewhere. These beds will not need organic matter for a few years. This helps create a soil that holds moisture and the plants grow well. It has been useful for the slope and to improve the poorest soil. The ridges formed might reduce runoff. The effort and time limit how much is done each year. I enjoy seeing the soil and curious stones.
The upper gardens with sandy soil are the quickest to warm up and last to freeze extending my season. Some perennial herbs benefit from the drainage and may be used in ridges or trenches. My lower garden had shallow sand over the sandy gravel. A deep layer of rotten leaves helped. I planted potatoes in deep trenches with lime and fertilizer at the bottom of the trench and placed the potatoes. As I back filled I added organic materials with our acidic soils. Since the tubers grow in the acid soil they are free of scab and diseases but the roots are in the limed soil so the nutrients are available. I do not water enough after flowering when tubers are developing to have heavy potato production as watering is limited. It works and improves the soil. And I have sometimes replanted deep while harvesting for a volunteer crop. This is a small garden not a field. Local disease and other conditions may not allow such a practice in other situations. Potatoes can be used to clean a field (or fence row) of perennial growth as the row is dug twice a year.
I tend to plant in trenches on the slope shoveling soil uphill. From the nearby shore seaweed and local manure has improved vegetable and fruit growth on the sandy soil. Mulches on paths can reduce runoff and be thrown on planting beds after foot traffic has broken it up and reduced it. The challenges are opportunities to try ideas out.
Some rock gardeners would value the drainage.

[ottawagardener]

Thanks for your experiences traab. I did terrace the hill and the path that is at the highest level is sodded to reduce/eliminate erosion. It is just the first year but so far, there has been an increase in the number of earthworms. This area is an old orchard so it is being interplanted with perennial edibles and cover crops mostly.

I also terraced another small hill that has a rock in the middle. The beds are more or less circular there. I'll have to take some pictures.

[Joseph Lofthouse]

Finally, after about 10 years, water again flowed down the major ravines out at the ranch. It was a flash flood that washed out many of the water control structures I had built.

Lessons learned.

• Flash floods on steep slopes are awesome!!! Meaning they are tremendously powerful.
  
• 400 pound boulders were not an obstacle. The 5 foot deep water just lifted them up and carried them downstream.
  
• Small swales and berms on or near contour survived well. Even where they overflowed and/or ruptured, it lead to sheet flow and not erosive ravine cutting.
  
• I like micro-checkdams across swales. Very nice to have transient puddles.
  
• A lot of sediment (mostly silt) got deposited into the swales. They need to be cleaned out and the berms made higher. Swales with a bit more slope to them deepened themselves and did not silt up. The bottoms are now lined with small gravel.
  
• Some check dams built on top of bedrock survived in the larger ravines, but all built on soil failed due to undercutting from not having an apron after the checkdam and not being keyed into the bank/bottom. (oops!)
  
• Rocks should be placed with care on the checkdams so that the water pressure presses them more tightly against each other.
  
• Gabion baskets may have helped.
  
• Tossing soil onto the upslope side of the check dam after construction lead to better survivability.
  
• Bedrock spillways are tremendously cool.
  
• Tree roots and branches are very resistant to flash flood erosion.
  
• Any checkdam that survived is now filled with sediment.
  
• A tremendous amount of water flowed off the hard surface of the dirt road, but alas, there were no water control structures in place to slow it down or redirect it. Swales across the road would be very useful.

I was most pleased with the performance of the small micro-catchments: puddles two inches deep and three feet across. Those I can build and maintain at no expense and with little experience or labor. In many cases, it would be a simple thing to expand the puddle to three inches deep and four feet across.

The failure of the large checkdams in the big ravines represents a lot of labor and resources. Any future earthworks I do in the largest ravine will be more carefully engineered. I think that I won't build any checkdams in that ravine unless they are in gabions. Keyed checkdams with aprons should work fine in the smaller ravines without using gabions.

[Joseph Lofthouse]

I spent the week building weirs and swales. I didn't get photos of the swales, or the smaller free-stone weirs. I'm liking the smaller structures. Things that are a foot tall in the small runoff channels. They are easy to build and likely to survive any flash flooding.

This video shows a gabion rock weir that took two long hard days to build. It contains about 38 cubic feet of stone inside the gabion, and about 4 cubic feet of stone in that sorry excuse for an apron. If I build another one of these, I will collect the stone ahead of time, a little bit at a time, and pile it on the bank prior to construction of the weir.
youtu.be/a__AQmqQ64o

This video shows a wire fence weir that is designed to catch brush and debris floating on the flash floods that are so typical of this ravine. It was placed in a location where a tree was already acting as a semi-weir. The posts were driven until they reached bedrock.
youtu.be/TJ6Zvrq3e7w