More on Brazil Land slides - Rio de Janeiro State

Felipe Dana, has photographed very graphically some of the recent land slides in Rio de Janeiro State in Brazil.  The effect on people, property, and the topography has been devastating. see his slideshow


 The aftermath of such slippage as in the case of João Henrique  of Itaipava was contained and mitigated through the primary use of vetiver.  Luiz Lucena of DEFLOR is one of Brazil's leading advocates for the Vetiver System for slope stabilization.  He writes:


"Referring to Rio de Janeiro landslides, they occur all along our coastal mountain range called “Serra do Mar” where shallow soils lay right over the rock. The problem is always the water: under heavy rains, the subsurface flows are very strong and once associated to the slippery rock result in landslides. The process begins with subsurface flows transporting soil particles until all friction is gone. In these areas, Vetiver has influence in many different ways: 1) it reduces runoff speed, thus increasing infiltration what may contribute for the landslide process; 2) It also reduces speed of subsurface flows reducing erosion process thus avoiding the activation of the landslide process; 3) where the rock is fractured Vetiver will work as anchor.

I strongly recommend Vetiver for similar conditions, not only on the plains but also for the slopes, under the following concerns:

1)    Previous Geological / Geotechnical study to confirm technical solution and identification of risks such as rockfall, for example;

2)    Determination of the spacing and position of the hedgerows or plants alone - in case of using Vetiver as a GREEN NAILING as we have been calling the introduction of Vetiver spaced minimum 0.5 m (in reference to SOIL NAILING already used in traditional engineering);

3)    MONITORING:  as long as water drained in the bottom of slope is clear and free of sediment the structure is working and risk of failure is limited.

We have helped Mr. Joao Eboli in his work at Itaipava, Rio de Janeiro State, one of the major centers of the recent catastrophe. Paul Truong and I visited the place a little over one month prior to the climate event reported. After the rains I called Mr. Eboli to check if his slope had any damage ,and from his report the most important was that he noted that the water in the lower part of his property was coming out totally clear, free of sediment, while his neighbor was experiencing soil loss and risk."

I would add that vetiver hedge rows spread the water more evenly across potential slip slopes, thus reducing potential high water pressure/soil saturation areas that might might be the point where the slip starts.  Also in the hot tropics vetiver is likely to pump out quite a lot of soil retained water, thus reducing soil water saturation prior to new rainfall events.

The Vetiver System may not fix it all, but it could bring a much higher degree of stability if applied to potential slip slopes and for slip mitigation and repair.