To swale or not to swale.. that is the question!

Hello,

I have a piece of property in the foothills of the coastal range in Oregon and I am interested in making a forest garden for commercial food production. The area that I am interested in doing this work is a triangular piece of property that is about 6 acres. The soil conditions are a little strange, but I think it is workable. Some areas have a clay pan that is about 2 feet under the top soil. There is even an area where the bedrock is coming through. It has several annual streams that go through it. Currently the land is a forest that has been logged and it doesn't seem to be in good health; the trees are mainly hawthorn, an occasional fir, and tons scotch broom and some out-of-control blackberry patches (among logging slash piles). The patch of land is at the lowest point in the property and there is a spring that is higher in altitude that could potentially be used for irrigation.

Anyways, the summers are very dry here but the winters are very wet. The site receives something on the order of 50" of rain per year. What my current (uneducated) vision is, is that I would like to add swales on-contour every 15' or so and then plant on the berms. I like this idea because the annual streams could be redistributed across a large area of land which, eventually, would make it so that I can last through summer without irrigating. Additionally, it allows me to have a berm so that the trees could be raised up out of the wet soil in the winter. However, I am uncertain if this would be an excessive (or even correct?) usage of swales. For example, it would seem that the soil is quite wet in the winter time; is it possible to have even more water (how would I know?). Do the swales make the water that is put into the soil in the winter last longer into the summer - potentially the entire summer?

If I were to put swales every ~15', it would seem that the amount of water collected in down-hill swales would be somewhat small as it would only catch a small-ish portion of the run-off. In general, would this nullify the effect of the prospective swale?

Finally, if the soil is somewhat saturated in the winter time, does this mean that I shouldn't even bother with swales? i.e., would the swales be redundant and extra cost that is not needed?

Any insight and/or opinions would be appreciated. The property is in USDA zone 8b.

Thanks!

Chris

The swale is a good idea. I would however let the stream follow it's natural course in the winter and maybe in the summer let it irrigate the swale. You also mention that the bottom section of swale will not have running/standing water, this is a good thing you want the water in the swale uphill to flow downhill underground esp in the summer vs just get evaporate. You can also do a pond setup that you fill for 6day and then empty to flash flood all swales.

One thing that I feel compelled to mention is that the existance of the stream is a relatively recent thing. It developed after the road was ditched and a culvert was installed which redirected a bunch of runoff from higher up on the property.

How would you suggest that I let the stream irrigate the swale in the summer time? It would seem that I would need some sort of wier or something to block the stream such that it is redirected to fill the swale (assume that the stream direction is perpendicular to the swales).

Also, around June we stop getting any rain at all so it would seem that I would need to flood the swales in the spring time. Does that make sense?

Finally, what are your thoughts on the swale spacing/frequency down the slope of the hill?

Thanks for the help!

Chris

Swales every 15' sounds too close, not enough room for the tree canopy and to get between it to harvest.

The lower swales may not have much catchment initially, but that corrects itself quickly either by overflow of the upper swales or by springs forming from the infiltrated water up slope.

I agree with R. Scott, you want to space your swales with the idea that your trees will have sufficient room to grow and you will have access to them. Over time, the swales will result in your soil having a much greater water reservoir within it, so it may be that eventually no summer irrigation will be needed. Probably worth looking into how trees of the varieties you intend to grow perform in your area, they may be adapted to the wet dry cycle of your seasons and irrigation may be less of an issue than you anticipate.

I have no comment on the swales but if you have some bush/woody problems of any sort than your property is crying out for goats!

Ditching causes you extra run-off. How does one deal with property edges, and introducing extra run-off to your neighbors??? Can one really catch everything? Is that wise? How do you manage run-off to neighbors?

Also, I would think swale numbers and spacing depend on property steepness, abundance of rain, run-off, and natural sources of water, as well as feed/food/forest management. For instance, my 10 acres probably only has a 4 foot elevation swing from border to border. I'm thinking I need no more than 2-3 swales for my annual rainfall (24"), no streams, and little ditch run-off. That's my wild guess. Any ideas?

Knobby Tires

In regard to the number of swales, I was thinking about having a swale frequently so that I can plant in the down-hill berm. However, I am uncertain if that is too frequent or not. In other words, that would be something on the order of every 20 feet or so but it could vary based on the hill profile. In my case, I think my top to bottom elevation change is something on the order of 50-70 feet? From a cost perspective, installing that many swales may not be wise....

The ditching was due to a road that was installed (originally by a logging company) that cuts across the hill side. Therefore, all of the run-off from up-hill is collected and then it goes through a culvert on to the area of the property that I want to plant on. It seems to be an excessive amount of water to me..

Fred Patrick wrote:Ditching causes you extra run-off. How does one deal with property edges, and introducing extra run-off to your neighbors??? Can one really catch everything? Is that wise? How do you manage run-off to neighbors?

Also, I would think swale numbers and spacing depend on property steepness, abundance of rain, run-off, and natural sources of water, as well as feed/food/forest management. For instance, my 10 acres probably only has a 4 foot elevation swing from border to border. I'm thinking I need no more than 2-3 swales for my annual rainfall (24"), no streams, and little ditch run-off. That's my wild guess. Any ideas?

Knobby Tires

Fred, there is math for figuring out what you need. I have not integrated the information yet myelf, but if you look for discussions about capturing roof runoff and storage, you will find the formula for how much water is coming off each square foot in a rain event. And you can calculate what a given size swale will hold. With those formulae, you can determine what the runoff volume is, and what you will need in the way of swales.

The angle of the slope does not effect the amount of the water flow, but the pace of movement, and it might make sense to have deeper swales if the slope is steeper, not to hold more, but to catch and restrain the fast moving water.

As I understand it, the first question is measuring the catchment area to be served by the swales, then to consider the size of individual rain events you can expect. From there you can calculate what your swales need to be to manage your rain events.

As far as ditches increasing runoff; it would be interesting to measure that and determine whether they just concentrate the runoff, or if they actually lead to more water running off. My guess is it is mostly a matter of concentration.
Runoff on to neighboring property is happening with any measurable rain event. Concentrating it and letting that run onto the neigbors' land might not be the nicest thing to do
Swales act to reduce runoff by slowing water and infiltrating it into the land, so if we want to reduce runoff onto neighbors' land and keep it for our own use, swales are a good method.

Hi Chris,

your land sound a lot like my land. Mine is on the mountains near Madrid in Spain and it's like it's got two personalities: wet and cold in winter, hot and dry in summer. I also have lots of runoff that deposit soil in the lower areas and erosion in the higher areas (my land looks a little like a soup dish cut in two). Some areas are watter logged in winter and completely dry in summer. I have a seasonal pond. I also have 2 springs that dry out in summer, but we are cleaning them with an expert that says they will have water year around when they are clean (keep your fingers crossed for that!). I have granitic rock in the subsoil and it emerges in many places. The depth of soil varies tremendously. I have lots of blackberry bushes and grasses, evergreen oak and the tree that has beeries to make gin (that's the scientific name, of course). The wetter areas have no tree coverage.

I have decided not to swale, for these reasons:

- I am not sure I can actually excavate a whole swale without meeting rock, so my swales would constantly be interrupted.
- My land needs to build up soil, not to excavate the soil it does has.
- Swales would not work right now because I have little soil with no organic content and right under I have rock. Water that does enter the soil quickly saturales it and then slips down the rock and away from my property. Swales work when you have soil to absorb and stock your water.

So, instead:

- I have stopped cutting down the grass and have banned all herbivores to build up natural mulch (I am getting lots of critiques because of the fire hazard)
- In open fields, I am planning to make micro terraces by making small rock lines or tree trunk lines on contour and planting colonizing shrubs and trees to prevent erosion, build soil and retain water. My plan here (in Spanish, but there are pictures and a video in English: http://unasuertedetierra.blogspot.com.es/2014/06/erosion-en-el-prado-grande.html
- In areas around big rock out crops, I am building stone terraces that will benefit from the heat stored my the rocks during the day and the run off from the rocks. I am filling them with manure, leaves, tree cutting (all those foraged from what other people consider waste) and soil excavated in one of our springs when we cleaned it. Here there are some pictures: http://unasuertedetierra.blogspot.com.es/2014/10/la-terraza-del-aparcamiento.html and after we covered it with stone: http://unasuertedetierra.blogspot.com.es/2015/01/muro-de-piedra-para-la-terraza-del.html

Do you have pictures of your land (I'm a sucker for those!)?

Cheers,
Lucía

Chris ~ I hope that you will see this. I just found your post about swales. I read it with interest because we are struggling with this mystery also in the Cascade foothills of northern Washington. What did you decide from this discussion? Did you build swales and what were the results?

Thanks!

The distance between your swales is determined by the trees you want to plant.
If all you are planting are trees that only get to 12ft at maturity and you plan on picking by hand then every 15ft is ok.
If your trees will be semi-dwarfs at 18ft + 6 ft berry plants/support species underneath then having them 24ft apart might just be ok.
If you plan on having 30ft nut trees and using machinery to harvest or having herbivores underneath. The the swales should be at least 60ft apart.

As long as the plants are dormant in the winter, the saturated soil or frozen soil will not affect the plants but in the active spring it would.
Due to your dry summer, I would use plants with deeper root systems, ones that doesn't require staking/etc. So semi-dwarf, full size trees, or plant seeds and then top work them with a graft

Even if the swale cannot make entirely across the land, having a series of infiltration basin/pond is better than letting the water just leave.
You want the swales to be level, thus no running water, but once they full you should have a spillway so that the extra water can go on to the next swale/leave your property.

Need exacts, find someone you are comfortable with and give property layouts and access. 200 lineal ft can make the difference as to what are applicable plants and trees.

Sorry, but I cannot empathize, observation, and time. If you don't learn what you need to, within that time. Hire someone. NOBODY, knows what your land needs and wants without observation. If you observe, you will do research, and it will fall into place. There is no short term answer. Work on restoring the land first, before you decide to make permanent changes.