Question about swales and earthworks etc.

I have a section on my property sort of a triangle if you will  that I want to do a food forest in  about 65ft across the bottom and 135 ft down the sides.    over that 135 ft there is a drop of maybe 6-8 ft.

I was assuming no real need for major swales etc but now I am wondering if I should?    is there a rule of thumb for what slope starts requiring swales, terracing etc?

thanks

I don't know if there's a good rule for that or not, but the thing I'm going by on my property is based on runoff.  I go out while it's raining and try to see how much water is leaving the land.  If it looks like enough so that it would make a difference (especially if you're in a drier climate or your rainfall comes in spurts with droughts between), then I'd say it's probably a good idea.  If you go out in a good rainstorm and it looks like it's all soaking in, then they may not provide a lot of value.

If you're in an arid place, I think I'd just go for the swales no matter what.  But, if it doesn't look like you're losing much to runoff then maybe it's not so big a deal.  That's the process I'm using anyway, I guess time will tell whether it's good or not...

If you don't want to go with swales, another option I'm looking into that should help with water penetration is keyline plowing (basically a deep subsoil cut on contour).  According to the keyline folks, if you do that three or four years in a row and add compost tea and deep rooted plants to the knife cuts in the soil, you can build aerobic topsoil at a rate of several inches a year.  Haven't tried it myself yet though.

Ditto - mulch can store a lot (I haven't run into a good formula for inches of rain held by inches of mulch but I bet it is out there somewhere - maybe 1/2 inch of rain in a good mulch).  It depends on how quickly your soil percolates, and how fast your rain falls.  If you have a clay soil and get 2-3 inches in a rainfall event, than I'd say swales are a good thing.  I have lots of light rain, and a silt loam so I don't worry about it except if I am managing impervious surface sources of water.

Swales could help with infiltration into hydrophobic soil, usually found in arid areas, even if it is sandy.  Basins around tree plantings or soil imprinting would probably achieve the same thing on flat land - getting sufficient water in one spot in order to get infiltration.  Geoff Lawton's greening the desert is a good example of swales on relatively flat dryland (see youtube videos).

Knowing your specific rainfall/climate/soil type would help in answering the question.

Thanks guys,

I get just under 50 inches a year rainfall  with it being relatively even spread out over the year.  Feb the wettest  aug/sept drier but it still rains some.      I live in N.carolina mts    so I have the pretty typical somewhat clayey soil but its not that impervious clay they have someplaces.  It drains well.  I dont ever have sitting water even in flat spots.  (maybe due to rocks creating opening for drainage below the soil?)

Since you can get the hurricane dumps, it might be nice to cultivate a few wet spots to capture water when it really dumps.  I have enjoyed having hight and low spots in the food forest just to have the variety of moisture levels (vertical edge?) for different kinds of plant.

So its not just about water capture at the site scale, but also variable soil moisture at the patch scale.

You could even determine runoff when it is not raining by looking for exposed earth and signs of erosion or bits of vegetation carried down the slope by the water. 

I hate to have water run off my land and, in the middle of summer in north Georgia my rainwater harvesting storage tanks occasionally run dry.  So I have installed several contour ditches to enable water infiltration, which reduces irrigation needs - you can see some 'photos at www.nutrac.info.

Paul,  we only really get rain from gulf coast hurricanes here and usually the tail ends of it......i should have obviously mentioned this but the north long side of the triangle is bordered by a very small creek/ mt run off........so i do have that whole side of constantly moist edge.    I am planning on paw paws and elderberries for alot of that edge, maybe some persimmons as well

nutrac thanks for the site....what are thoose pics under?

Plenty of water, good drainage, sounds about perfect organick.  If you had sandy soil then I would guess it to be low in nutrients, but I think the clay should hold onto most of the good stuff.  Do things grow well for you in this area?

right now its just grass/ "weeds" but they grow well yes....I never water anything at my house but the garden and its all green.    the other side of the triangle is a driveway that acts as run off so I may dig a few entry points to direct that water back over the land......  I guess I am wondering if the work is worth the gain  or if tight planting heavy mulching etc would leave me about the same result.......I mean the swales could never really hurt if done right i guess.

Do you have any pictures Organick?

I'd dig a small swale to test with and see if it fills up in a moderate rainfall event.  If it does then perhaps there is a benefit to them.