Laos: Using brushwood to prevent riverbank erosion

A cost-effective technology using locally available materials and manpower provides a sustainable way of stemming riverbank erosion on the Mekong river in Laos, according to Phaknakhone Rattana from Laos’s Ministry of Public Works and Transport.

“A soda-mattress [also known as a fascine, or fascine mattress] is a structure made of brushwood and other materials to protect the riverbank from erosion,” Rattana told IRIN in Istanbul at the World Water Forum.

“It is a low cost and effective method because it is implemented using locally available material, like tree branches, stones, manpower, etc.”

A fascine is a rough bundle of brushwood used for strengthening an earthen structure, or making a path across uneven or wet terrain. Typical uses are for protecting the banks of streams from erosion or for covering marshy ground.

The soda-mattress system was introduced and developed in Japan in the late 19th and early 20th century and extensively used for groins and dyke-foot protection.

About 90 percent of Laos’s territory forms part of the Mekong river basin and riverbank erosion is one of the most serious forms of damage to the river, according to Laos’s MPWT.

The level or the Mekong river changes seasonally, with the lowest levels in spring and the highest in August-September when it rises to up to 10 metres above the lowest water levels, said Rattana.

The poor are the main victims of riverbank erosion, with their houses, community facilities and roads under threat of destruction, according to MPWT.

Rattana said the soda-mattresses were suitable for sandy riverbeds and had proved effective in protecting riverbanks. He noted that after the implementation of a pilot project in 2004, “when there was a rise in the water level, there was no erosion of the banks, and no damage to the people.”

Cost effective

He particularly emphasised the cost-effectiveness of the technology. “For instance, if we use the conventional ‘gabion’ method, it is very costly,” Rattana said.

He said that a conventional ‘gabion’ system deployed around Laos’s capital, Vientiane, on average cost about US$2,000 per square metre.

“If we take the combined work of cobble stone with willow branch work covering the whole bank, stone foundation and soda mattress, it costs $1,300 per square metre, thus saving $700 per square metre,” Rattana explained.

“The soda mattress, which is a very light structure, is very sustainable and lasts for more than 10 years,” Rattana said.

Flexible, durable

Another feature of the system is its flexibility and durability in water; it is porous which is good for aquatic habitats, effective against sand suction and adaptable to mild slope rivers, the MPWT official said.

“The pilot project of soda mattress installation on the Mekong river around Vientiane was carried out in 2004, and after the pilot stage we transferred this project to the countryside. Now we have three to five similar projects in the country and in one case the soda mattress is installed on a 5km section of the Mekong river,” Rattana said.

According to a statement by Viensavath Siphandone, director of Laos’s Department of Roads, at a Public Works Research and Development conference in Asia in October 2002, the government of Laos had only $100,000 a year to spend on riverbank protection measures. With this money the country could only protect 60m of riverbank using the ‘gabion’ method, which led to the search for more sustainable solutions, like the soda-mattress system.

The annual flood report by the Mekong River Commission in 2005 showed that the estimated damage (excluding damage to private infrastructure) caused by the 2005 floods in Laos was about $28.5 million.

at/cb