Swales in existing orchard?

So we have a relatively young orchard that is laid out in a pretty square grid with 15' between trees.  Unfortunately it's on an irregular slope, and I'm concerned much of the water will run off.

I'm considering renting a small backhoe and simply trenching down the center of each row to build quasi-swales to help with water retention, but I'm not sure how effective that will be.  As long as I do something in the next year or so, it won't tweak the trees at all.

Before I do that, has anyone ever dealt with a similar situation and if so, would you care to share any lessons learned?

swales would not go down the centre of rows they follow the level like terraces they go round following the line of the hill. so you would have S's curving through your grid.
   They are like steps when the step slants slightley into the hill so the water goes into the hill way instead of down the hill direction.
  They are, if you have space, my hill is too steep to put in more than narrow shelfs on the hill, like very wide irrigation ditchesl. Wide because as you want the water to sink into the ground you want as much water as possible in contact with the ground so it will sink in.
    Irrigation ditches are built to be lower at one end than the other, they are built to carry water off the land while swales are built on the level so as to stop the water running out of them. If the water leaves the swale it should be because you have left the wall or bank that runs along the lower side of the swale lower in one place for the water to overflow out of the swale. You leave the swale wall a bit lower where the water can overflow into a lower swale beause you have provided a channel that leads to a lower swale.
  You put your drip watering system on top  of the berms following the contour of the hill rather than running straight from tree to tree, though it is also possible that you plant your trees on top of the berms as in geoff Lawtons greening the ddesert videos.
    Berms are  banks made on the lower bank of the swales, you can make swales just by putting a bank along line of the hill that stops the water going down hill and obliges it to stand at the level the berm is built at.
  Berms and swales are built like contour lines, to go round the hill at a certain altitude or height. That is berms that accompany swales are, berms can have other uses. agri rose macaskie. 

Rose is right, but there is an alternative: you can dig 'boxes' in the aisles to make each tree the center of a small terrace or paddy - this will increase water retention and achieve the same goals as swaling. A swale or berm can run as a system that is of any length provided it is on the contour. If you don't follow the contour, you need small, contained units, you need to think in terms of pockets.

      If you build swales in the orchard they should keep the whole area damper than it would be if the water ran off the surface of the area. they don't have to go just next to each tree. They might never appear to have water in them they just stop water from running down the hill if you want to see rainwater running down the hill you have to go out an dsee whats happening in a thunder storm.
    What Jonathon Byron says is right if instead of having flat ground that water can run off we have bumpy ground with lots of dips for puddling, if water puddles then it sits on the ground.
      In the mediteranean they dig a hole round the foot of the trees a sort of basin at the foot of the trees called alccorque. I have a gravely slope on which the presence of alcorques made the sandy gravely soil push out below them, bulge up, there was erosion just below the surface that pushed soil up onto the surface. it could be that swales might desestababize slopesn aqnd cause landslides it might be best not to make them on very steep slopes, I dont know about this aspect of swales.  agri rose macaskie.

The "Boxing" idea seems useful.
Bear in mind that it will be difficult to mow between the trees unless
you're into scythes.
Short overlapping swales could work too, again they will be in the aisles
and not easy to do mowing.
Groundcovers to smother out weeds and provide nitrogen to the rootzones
could be an answer to not mowing.

I'd try this:  

With a two share plough go down the center of each aisle, and cross between the trees.  Let it sit over the winter.  The freeze/thaw cycles will break up the sod.

Make a pass with either a narrow set of disks or a rototiller.

Make a third double pass with a blade set on an angle, one end about 3 inches above the other.

What you are trying to do is to shape a berm about 2-3 inches high and 6-10 feet wide.  

The disturbed soil with settle, and you may have to repeat every few years.


Or try this:

For this you need an odd attachment -- a chisel plough with coulters.   These are commonly used to break up hard pan.  Coulters allow it to be used in a zero till setting.

Requires a fair amount of tractor:  I have a 55 hp Deutz and it is all it can do to handle a 7 share chisel plough.

Anyway after a pass on the surface all you see is about a 2" wide disturbed section where the shank of the chisel passed through the soil.  Repeat each fall

In effect you have left a disturbed path of dirt about 18" deep and  2 inches wide for each chisel.  This won't help a lot with heavy rains, but should work well for spring melt, and steady light rains.