However, many of the walls have been undermined by rain and are in danger of collapse, threatening the survival of some of the houses themselves.

This was confirmed in a report from the Lam Dong Department of Construction. It said up to 80 per cent of building works, particularly houses, roads and bridges, were in danger.

Nguyen Duc Thiem, the owner of a house at 25/4 in Suoi Cat-Xuan An, Ward 3, in Da Lat City, said that after an hour of heavy rain on May 5, small cracks appeared in the retaining wall in his front yard.

Thiem said the wall was 15 metres long and 8 metres high. It was built by a former house owner in 1980.

"In the year 2000, I re-inforced the wall's foundations, thinking that I would not have to worry again about soil erosion during the monsoon season," Thiem said.

However, when he woke up on May 6, he found that a 15-metre-long section of the wall had collapsed and slid onto two neighbouring houses. "And the next day, the whole wall collapsed," Thiem said.

Vo Van Luyen, the owner of the neighbouring house, said he was stunned by the incident. "When the wall collapsed, my wife and I were about to water the plants in our garden. "We narrowly escaped death," he said.

Luyen said, he and other people living at the foot of Thiem's retaining wall had asked the owner many times to consolidate the wall. However, Luyen admitted, that this was a difficult job.

Le Van Nam, a resident living in Dao Duy Tu lane in Ward 4, said his house was next to a 15m high and 100m long retaining wall, which was in a bad state of repair. It imposed a constant threat to his family and others, particularly in the monsoon season.

He said that on May 3, a 10m high section of the wall collapsed and buried a seven-seat taxi.

Le Quang Trung, deputy director of Lam Dong Department of Construction, said up to 80 per cent of houses in the city had retaining walls, which were an architectural characteristics of Da Lat City. Houses were even built on 75 degree slopes.

Trung said big buildings like those in Hoa Binh area, Ward 1, were surrounded by retaining walls up to 15-metres high and 200 to 300 metres long. The walls were regularly maintained. But competent authorities found maintenance work of thousands of retaining walls under the impact of human beings and natural environment a big problem.

Trung has asked people living at the foot of a steep slope to report immediately to his department whenever they found cracks in walls, particularly those supporting roads. 

VNS