Swales, dams and steep slopes

Discussion in 'Planting, growing, nurturing Plants' started by jimmys, Nov 1, 2004.

  1. jimmys

    jimmys New Member

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    Hi all,

    I know it is difficult to give a definitive answer, but what is a ballpark gradient figure for safe construction of swales in steeper country ie. >20degrees?

    In the northeast of India, there are problems with landslides, the soil is red (both clays and clay loams) and I have had lots of interest in the swale idea. However, I have never undertaken such a project in such country. SALT (sloping agriculture land technique) has been used in various parts.

    I have scoured the web for anything on slopes and swales but there is very little available. I also have Water for every Farm at hand but it does not really use the swale i.e. on contour approach, that PC uses.

    Can anyone give any advice before we go and create even more landslides given it takes a lot of work to create swales in the first place, and the subsequent damage can be life taking (as has occurred here many time over the past weeks, and months after the floods).

    It's interesting that a lot of PC development uses swales and yet there is not a lot of information available on their construction. And it is definitely one design and implementation aspect that PC practitioners need to be responsible about.

    I look forward to your responses,

    Peace

    James
     
  2. gardenlen

    gardenlen Group for banned users

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    g'day james,

    mm dunno mate i have 6% slopes by my reckoning about what you are talking about at 20 degrees. i have sandy loams through to heavy clays.

    what i used for swales is i have planted all my trees along the contours this i see would be needed to stabilise your situation (i'm only guessing/assuming ok), i then used a single ripper towed behind the tractor to rip a narrow furrow app' 20"s deep, i have also created swales with long rows of mulch along the food trees planted along the contours. i have found with these types of swaling systems i use you don't need to be exact along the contour as you would need to be with a trench and berm swale, also the ones i use aren't as labour intensive.

    from where i stand if the soil is unstable and prone to slides then trees with deep roots are going to be needed to stabalise that problem.

    other swaling methods would be rows of mulch bales with a peg to hold them until they establish, or the taller tuffed grasses like lemon grass & citronella grass, planted in double or triple rows alternately, they will capture debree and build into a swale mode.

    for me i think deep rooted trees are gong to be needed in your situ' to stabalise the soil these rows of trees along the contours could be about 10 to 15 meters between rows. as i can't see what you have i can only guestimate.

    the methods i used as stated above have done a lot to give me moist soil and drought proof our land, and all with low impact on our landscape all is as permanent as you want or as temporary as you want, and for me low cost and low imput of manual labor or exactness.

    len 8)
     
  3. Nik

    Nik Junior Member

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    steep swales

    Are the Landslides caused by earth tremors or saturated soils mobilising on the steep slopes?
     
  4. Justin Robinson

    Justin Robinson Junior Member

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    Vetiver grass has been used on steep slopes in the tropics and subtropics, it's a prolific grower (so take lots of care if considering introducing it to a new area) and planted on contour will grow thick enough to eventually catch soil behind the clumps and form a small terraced area behind the plant, I know for sure the oil from this grass has insecticidal properties, and has been used effectively in Malaysia for slope stabilisation, but thats all I know and have'nt grown it personally, yet a surf on this web will probably find you more info.

    good luck!

    cheers.
     
  5. gardenlen

    gardenlen Group for banned users

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    never thought of the grasses justin,

    i wonder how citronella grass would go? it has a very strong root system, grows to around 2 meters tall, i have it here and it spreads in ever increasing clump size so would be easy to control, mine gets a flower head but have never seen viable seed from it, and the stuff i have planted is pretty much still where i planted it, it will also take it dry once established.

    len
     
  6. Richard on Maui

    Richard on Maui Junior Member

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    slopes too steep for swales?

    I too have wondered about the wisdom of digging swales on too steep sites. I am almost positive that I have read something by Mollison on the subject in one of his tomes but I can't remember where and don't have any of his stuff with me here, except for Introduction to Permaculture. Tonight I will probably take it to bed and read the very passage.
    Are you sure that Yeomans doesn't talk about swales? His contour ditches that connect his keypoints are basically swales, right?
    Anyway, I guess the key, whereever you are disturbing soil is to plant plant plant and mulch mulch mulch, and of course in the particular case of swales, they are designed to facilitate the reintroduction of trees into the landscape, so as well as your lemongrasses and citronellas and vetivers don't forget to plant your trees and bamboos with root systems big enough to hold all that soil... Fast growing pioneers as well as the climax species...
     

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