Slope Stabilization

Plant a load of trees, then.

Can you find some old tires? This would be inexpensive but labor intensive, follow up by planting vegetation.

I think the tire solution is excellent. We have serious landslide problems here, many places where roads were cut into the hills left slopes steeper than 45 degrees. Heavy rain caused landslides, which prompted very expensive retaining walls. Tires are a disposal problem here, they pile up at the landfill, bureaucratic nonsense.

On our property here, we have had one expensive slide, put up a $10K wall only 20 feet long. Above it we installed a treated lumber 'ladder' set into the dirt, with it's base at the wall. It's holding so far, but other places on the hill have large cracks in the soil, so it's just a matter of time. We have the hill planted with shrubs, but it is still slipping.

At least in the OPs situation, the hill is at the natural slope for the soil used. Compacting the soil and doing something to keep rain from cutting into the soil will help. We put a curb border at the top of our hill, to deflect the water away.

Kudzu was tried by the Highway Department,(in the US) but it likes to take over, is a real pest plant. I use a local grass, which spreads quickly, and hope it sheds the rain downhill. It has a purple (maroon?) tassel which looks like wheat fields when it matures.

I'm surrounded by kudzu, it takes over everything and kills the native vegetation, including trees. It dies back in the winter, but in summer it will grow 1 foot a day. I could see it becoming a real problem in the Virgin Islands where it stays warmer.

In the OP's case I don't think hiring an engineer is an option. It's a great use of used tires, which are a problem everywhere.

I cringe/laugh to think of what this little island would look like if Kudzu ever got here. I remember seeing it overgrowing trees on the interstate in Virginia and North Carolina.

The thing with trees is it takes so long for them to grow and develop roots enough to hold a hill. When our hill let go, it took out trees twenty feet tall. I'm sure everybody has seen the videos of landslides running down roads knocking everything out of the way.

I favor a plant with a dense root mat right at the soil, to keep rain from rapidly penetrating the soil, like grass. There is a grass here we call 'goat grass', it grows in culmps and has a dense root. It grows fast and spreads fairly easily. A whole hill of it would probably shed rain like a coat of fur, only allowing enough to soak in to keep the grass alive.

Hire a qualified Geotechnical Engineer who is licensed and registered to conceive a plan of action.......vegatation alone will not solve the ongoing slope stability problems in the long run.

I'm guessing from the information given that you don't have funding for a geotechnical engineer, but are looking at this from a community project standpoint.

Bioengineering for stability is all about the below-ground architecture - the rooting patterns of different species. Smaller plants or groundcovers are often used to control erosion of topsoil but they will not prevent the whole bank from turning into a mudslide if the area has heavy rainfall. You need fast-growing and deep rooting species, and you need some complementary species with spreading but not shallow rooting patterns, to optimize the net stabilization effect once the trees are established.

The quality of the fill is also an issue: more and bigger rocks in the mix is hopefully the sort of fill the local authority has used for the purpose.

So the question is, where are you located, and what are the native tree species available to use for the job.

I looked around and found some links to resources that might be useful to design a solution to your problem.

This paper is about modelling four different types of root architecture (as found in different tree species) and comparing their capability to stabilize slopes:

http://www.springerlink.com/content/w1j6431g72u5pl27/

Another paper modelling spatial distributions of root architecture for stability:

http://aob.oxfordjournals.org/content/101/8/1281.abstract

This book chapter provides some basics: how vegetation reinforces soil on slopes:

http://www.springerlink.com/content/lr2050u7516t7417/

Scientists who develop software for their research are often willing to share those tools with others: you may be able to get a copy just by asking the authors.

Hi all

thanks for your inputs. This is a community project in Assam, India. Very little budget.

shantanoo

Wow. You may not have much budget, but you have a wealth of biodiversity in Assam to choose from. Obviously you need to choose the species that are right for your ecoregion or forest type, as well as good choices for stabilizing a slope. I would expect that the Assam department of environment will be able to give you information and help you to find seeds for your project.

To give you an example of root architecture with trees native to Assam, the mango (if it belongs to your ecoregion) could be a good choice as an anchor tree species for your slope, because it has a deep taproot type system and is also fast growing. Neem and Eucalyptus also have taproot type anchorage. Whereas the Ficus species such as banyan and peepal are not a good choice for that purpose, they are shallow rooted and will grow on the surface without anchoring the slope. Your own department of environment people can give you just the right help in choosing the best plants for the soil type and ecoregion, and which community of plants or other trees will do best in company with the anchoring tree.

And by the way, Kramarat's suggestion about tires is a good one, or else some simple structural "pockets" formed from the earth are the usual way to plant trees on a steep slope, to encourage rainfall to pool and penetrate around the tree instead of running down the slope surface. A berm or a hump on the downward slope side and a swale on the upward side, as shown in diagram f. here. Good luck!

the curb at the top of the slope is good,have it drain to a low spot in the curb line and install a slope drain . it would depend how long of an area you are trying to protect for the amount of drains.they are very simple.kind of as if you cut a pipe in half long wise with half of a funnel or wing wall at the top with the half pipe going down the slope. on the slope you could use soil stabilization matting and plant crown vetch,if they have it where you are.it is a low laying plant that spreads outward,and is used here. the down side it take awhile to take hold. you can also look into soil cement.i have never used it but i hear it helps