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Access road = Swale? Drainage ditch? Help!

 
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I'm trying to design the access road that gets me from my property entrance to my future house site, which would be about 100-200m from the entrance (see picture below).

What's the usual permaculture approach to access roads?

...Reading and re-reading my Permaculture Design Manual I get that I should try to position roads roughly on a contour, but beyond this I just can't figure out what I should DO with the access road exactly. Should I turn it into a swale? Or should it just be a drainage ditch...and put swales elsewhere (like above/below the road)?

As you can see in my picture below, my thinking was to build up a wall to allow me to cross the gully (thus keeping the road level/on contour). This would leave me with a potential dam site on the upper side of the wall I suppose. I've then followed the countour around to the house site.

Thoughts?
topo-map-access-1.jpg
[Thumbnail for topo-map-access-1.jpg]
 
N Taylor
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Woops. that image was frightfully big! here is a more manageable one in case that wont fit on your screen..

topo-map-access-1.jpg
[Thumbnail for topo-map-access-1.jpg]
 
steward
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Looks like a good plan. Just be sure that the dam doesn't wash out in a large water event.
Running the road on contour allows you to move any water that does over flow the dam, along the swale all across your land.
In this case all the way to your homesite. The water soaks in and your plants gain that water.
How much water do you get there?
 
N Taylor
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Miles Flansburg wrote:Looks like a good plan. Just be sure that the dam doesn't wash out in a large water event.
Running the road on contour allows you to move any water that does over flow the dam, along the swale all across your land.
In this case all the way to your homesite. The water soaks in and your plants gain that water.
How much water do you get there?



Thanks Miles.

So you're saying that many would make the road double as a swale, in a case like this?
Does the swale typically sit on the left (top) side of the road, or the right (bottom)?

Rainfall is 51" / 1300mm annually, climate subtropical.
 
Miles Flansburg
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Yes, one of the things that has been discussed is stacking functions by using a road as a swale. I would think the swale would be on the uphill side, but you could have several swales in the overall plan.

That is a lot of water, I do not have any direct experience with that much, so you would have to decide how much water you want/need to move across your land, and avoid any chances of washing out your road or dam.
 
N Taylor
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Thanks Miles - that's a fair point regarding being careful to ensure whatever I build will handle the volume of water moving down the landscape.

I'm trying to picture how a road/swale (or even diversion) could be configured in this sort of arrangement (access road following the contour, rather than the ridge top).

I've sketched some variations below - are any of these configurations better than the other?
access-swale-options.jpg
[Thumbnail for access-swale-options.jpg]
 
pollinator
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Don't know much about roads/swales, but...

Doesn't a swale water into the ground? If it's above a road, then wouldn't it put water into the road bed? Is this desireable?

Just a thought.


Rufus
 
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I think the idea of the pond and dam is a good idea.

I would make sure that the road has a crown. The only time I might have it purely slope one way or the other is for corners.

If you need earthworks projects, then this is a great time to plan in swales. Otherwise, I would focus on other stuff and put the swales in later.

 
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Your soil type becomes an issue as well. Increasing the moisture content of the sub-base of a road makes road maintenance more difficult if you're on a silt/clay soil. You will get soft spots and the fine soil particles will migrate into your gravel road as you drive over it. Sandy base soils have less cohesion, making erosion more of an issue. In that case, try to design more flat retention areas and larger sills so the water moves slower through the system.
 
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It seems to me that you want your road to be a road, not a water holding feature. Geoff has at least one video out there where he discusses road placement, emphasizes his preference for roads running on ridgelines and also discusses running roads on contour. My impression was that in any case, you want water to run off the road. As Paul said, the road should have a crown to it, thus ensuring water runs off the road, rather than sitting on it.

As others have mentioned, if you're going to have a swale alongside the roadway it ought to be on the downhill side, to avoid collecting water where it will damage the roadway.

If the road is going to double as a damn, you want to be sure you design the damn well, and you want to plan where you are going to have a spillway very carefully. In this case, it rather looks like finding a spillway that does not go across your road will be difficult. You may have no choice but to plan a spot where the damn would spill across the road way.

How much of your rain comes in large events? that probably needs to be considered, as the system should be prepared to handle the peak volume/flow situations.
 
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Roads and contour swales/ditches are addressed in a book on Keyline design I read years ago. I can't find my notes, but think things were 'best' arranged, from upslope to downslope, contour ditch - forest belt - road. I don't remember why. I'll keep looking through notes.
 
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Of your drawings the Number 4 is the correct idea. The crowned road being above (up hill) the swale which will collect water and created a down slope plume. You will also need an uphill side ditch to prevent water from washing across the road surface. This is to prevent the road surface degrading from run off. This ditch will need to be at least two feet from the edge of the road surface, sloping downward so the bottom of the ditch will be at least 1 foot below the road bed grade and a minimum of 24" wide, this is so it can handle most runoff situations without over flowing and degrading the road surface or road bed and the water can run away before the road bed becomes saturated and begin to degrade.

Any road needs a proper crown. These are usually best if they measure about 1 foot or less in height from the edge of the road surface to the center line of the road surface. When a road is crowned to high there becomes many issues that will degrade the road surface. Also if you don't create a proper ditch system that can carry away any runoff before it reaches the road surface proper, then you have a wash out scenario.

A water collecting swale on the down hill side will also need to be at least one road surface width distant from the road surface. This is so that water run off has to get away from the road bed before it is collected and thus help in keeping the road bed and surface dryer so it will not degrade from ground saturation. The road crown will also need regular maintenance to keep the proper shape and not get tire trenches, which deform the road crown.
 
N Taylor
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Ok thanks all - that is making a lot more sense now. I borrowed Yeomans keyline book and had a look at the road section, which helped somewhat too.
 
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