dikes

Suan Mali reforestation project

The dikes on the sloping land: Prevention of soil erosion

     The top soil consists of a thin layer of soil on top of porous red rock.
     Plowing is mostly done by small 2-wheel tractors. The warm season starts in February and the farmers hope for rain in April so the hard soil is softened and can be ploughed. If the rain is sufficient the cassava fetches roots and grows faster, when the rainy season sets in late May. If the rain is not sufficient the cassava dies and has to be re-planted.
     When the rain comes, the farmers start plowing. And if heavy rain follows plowing, then severe soil-erosion follows. To minimize soil erosion only the flat top hills should be ploughed. And the plowing should follow the contours of the land. The sloping land should be used only for tree planting.

The dike-experiment is preformed where the land starts sloping. The area was heavily eroded after only a few years of ploughing. The width is around 20 meters after which cliff like rocks follows. Even eucalyptus and wild bamboo have difficulty growing there.

October 1997 - Year 2:
The sloping land next to the cottage is still bare. Only a few small tamarind trees are trying to survive on the eroded slope.
The hills and valleys in the background are part of Phu Sri Than National Park.

April 1999 - Year 4:
The view from above has disappeared. And the tamarind tree is hiding in the middle of the picture among a wide range of self- grown trees.

May 2000 - year 5:
     The dikes are formed like long new- moon seals shorter than 30 meters long. They are highest on the mid, so that the water runs of at the end of the dike from where it continues down towards the middle of the next new-moon shaped dike. At the lowest dike there is an overflow on the edge of the rocks and with wild bamboo below - against erosion.
     The idea is to slow down the speed of the running water, so the soil sedimentation will take place in the deepest part of the water basin behind the dikes. Sediments are then once a year dug up to widening the dikes.
     After only 3 years the dikes are of such a size, so that, if they were spread out over the eroded area, they would make a 10 cm thick layer of topsoil.

The first moon-seal shaped dike with an overflow in the right end of the picture.
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June 2001: One dike north of the cottage keeps the cottage floor dry.

June 2001. 3 dike-systems south of the cottage.	August 2002: Water-gates of rocks.

August 2002: Showers with an intensity of 25 only fills up the first basin, so the dikes are seldom full.	August 2002: Heavy monsoon rain with 70-100 mm/day fills all the basins and the water runs of at the watergate.


Top hill	HOME	Pristine forest in the area
Sloping land	Link page	Conflicting interests
Dikes against erosion	Maps	Community forestation
The slope and the creek		Methods of reforestation
Forest fire		Botanical lists in Thai, Isan, Lao and English


Just after heavy rain. The top basin is full. full	But the water level drops fast, as the porous rock below forms no water barrier.	When the water is gone, a fast test shows more than 10 cm sedimentation.