Re-greening the forests
Twenty-five years ago, Huai Hong Khrai in Doi Saket district, Chiang Mai, was an arid land. Now, the area is turning green again
The materials are simple - bamboo, rocks, wood and earth. The construction is simple, too. The materials are placed together, the builders ensuring that they are strong enough to hold back the water flowing downstream. But the benefits of a check dam - a small dam in a gully to decrease the flow of water, reduce erosion and encourage the deposition of sediment - are far from ordinary. They can regenerate both nature and people's lives.
And the simple yet practical check dams were suggested by His Majesty King.
"When His Majesty visited the North of Thailand, he noticed how local villagers dammed mountain streams in order to retain water," said Pradab Kladkempetch, director of the Huai Hong Khrai Royal Development Study Centre.
The idea was later developed at the centre, where reforestation, small-scale irrigation, land development and farm technology are the focus of research to help improve the locals' livelihoods.
Twenty-five years ago, the area in Huai Hong Khrai in Doi Saket district, about 30km from Chiang Mai, was arid, the result of massive deforestation. Forest fires were annual occurrences, indicating the urgent need for reforestation.
"His Majesty, however, said that in the next 30 years, people would be jealous of the fertility of Doi Saket. And it became a reality, eventually," Pradab said.
Thanks to the naturally irrigated reforestation projects - including check dams - it took about seven years for the 1,360 hectare area to start turning green. New leaves began to bud. Flowers started to bloom and the wildlife slowly returned.
According to statistics collected by the centre, compared to 1984 there are now 60 to 80 more plant varieties, the mineral content of the soil has increased by three to four per cent and the temperature is lower by 1.7C.
Check dams are small barriers built across shallow rivers and streams. The small weirs retain excess water from monsoon rains, allowing time for water to be absorbed by the soil.
"The moisture spreads to nearby areas," the director explained, and by keeping the soil damp, the forest becomes fertile again more quickly.
More trees mean more leaves to decompose. And more decomposed biomatter means better soil, rich in nutrition, helping the ecosystem recover.
Increased moisture also reduces the chances of forest fires, one of the major causes of deforestation in the North.
"We can't say that humidity alone could prevent the fires, but it rather limits the areas where fires can start," said Pradab.
Farmers and residents in the area, who often face water shortages in the dry season, have also benefited from the check dams.
Check dams are not just useful in dry areas. When the monsoon rains come, these small water barriers slow down the flow of water running off mountains, helping to reduce erosion damage.
According to Rapeepol Taptimthong, an irrigation expert at Huai Hong Khrai Royal Development Study Centre, there are three kinds of check dams based on different materials. Simple check dams are made of local materials, such as wood, bamboo and earth, while semi-permanent dams are stronger, and use rock and clay in their construction. The strongest check dams are built with concrete and steel.
What materials to use is location-dependent. Check dams made of natural materials are suitable for streams in the highlands, where access to tools and equipment is limited, said Rapeepol. More durable materials should be used to construct dams where the current is stronger.
Though the purpose of check dams is mainly to hold back water, they are not meant to be totally impervious, like a plastic sheet.
"It's okay if a little water leaks through the dam. It's natural that water is absorbed through the soil," said Rapeepol.
The best period to construct a dam is in the dry season, when it is easier to check the quality of the soil - soil with too high a sand content should be avoided because of its poor ability to hold water. When a suitable spot is chosen, Rapeepol said loose soil and pebbles must be cleared away to prepare for construction.
There are no firm rules for building check dams, he stressed. Techniques can vary and be adjusted to suit different typographies.
Despite their simple construction, the benefits of check dams are great.
"What you need is local wisdom and a touch of creativity," Rapeepol noted. "For example, the best bamboo to use is large and thick. But if suitable bamboo is unavailable, villagers can drive smaller diameter bamboo poles into larger diameter lengths, to strengthen them."
Choosing the right location is important. Areas where streams are 3.5 to 5m wide and the water is shallow - between 0.5 and 1m - are perfect. After a bend is a good place too, since the water flow is normally reduced. However, if it is necessary to construct check dams across straight sections of streams, Rapeepol advises the building of several check dams, to reduce the power of the water.
Knowledge and check dams alone are not the most significant factors for regenerating deforested areas. The sense of belonging and ownership created by the participation of local communities in building and maintaining check dams is also very important.
The villagers have seen changes in nature. They saw how the forest near their villages became arid after trees were chopped down and how it affected their farming," Pradab said. "So they started to realise they should do something to bring nature back into balance."
Many communities seek advice about check dams, both the theory and practice, from the Huai Hong Khrai Centre. For example, about 200 villagers at Tambol Tha Pladuk, Mae Tha district, Lamphun, built 20 check dams in two days. "His Majesty the King once said that the key to protecting and nourishing nature effectively is local people," said the director.
Bangkok Post April 16, 2007