SINGAPORE - Bukit Batok Nature Park remains safe for visitors, as a section of it affected by recent mudslides is not accessible to the public, said the National Parks Board (NParks) on Friday (Nov 5).

This comes as residents have raised safety concerns over frequent mudslides off the face of a cliff at the park, which they said have been ongoing for close to two months.

In response to queries from The Straits Times, NParks' group director for conservation Lim Liang Jim said the incidents of slope failure could have been caused by "the loading of saturated soil above the cliff brought about by the heavy rains" in the past two months.

"As the section of the park affected by the slope failure incidents is not accessible to the public, the park is still safe for visitors.

"Access to the observation area at the quarry remains open, as the cliff is not linked to the observation area," he said.

A regular at the park, who wanted to be known only as Mr Tin, said he has observed mud falling down the cliff for close to two months in his twice-daily visits there.

"Mud has piled up ever since," said the 75-year-old retired engineering manager.

"I can even hear the sound at night from where I live," said the resident of a condominium in Hillview Avenue located about 600m away.

"It can get a bit scary if a bigger chunk of mud comes down," he added, noting that some large boulders and trees growing on the cliff had also been dislodged.

Mr Tin added that a smaller mudslide, which has since stopped, also occurred about two to three months ago at a nearby slope, closer to one of the transmitting towers of Bukit Batok Transmitting Station. "I'm worried that the mudslides will affect the tower."

Mr Lim from NParks said that other than the slope failure incidents at the quarry, there were another two such incidents between the quarry and a shelter at the park that had occurred in late August.

"The footpath between the quarry and Shelter E has since been closed for stabilisation works. For public safety, NParks would like to remind park visitors to keep to designated trails and not to go off trail," he added.

When The Straits Times visited the park at around 11.30am on Friday, there was a pile of sand-coloured mud at the foot of the cliff, which used to be part of a quarry.

Large boulders and tree branches were embedded within the pile.

Chunks of mud would intermittently break off the cliff, falling onto the pile below with a loud crack that reverberated throughout the quarry.

Mr Eric Tan, who was cycling in the park on Friday on his daily visit, also said the mudslide started around September.

"Big chunks came down initially, then smaller bits of debris more recently," said Mr Tan, who is in his 50s.

He noted that the cliff used to be pristine, with trees still growing on it.

Other parkgoers, however, felt the debris posed no immediate danger.

Educator Angeline Ho, 30, said that compared to the situation on Friday, the slope was "quite intact" on her last visit to the park in July.

She said she was elsewhere in the park when she heard a loud sound at around 11.15am.

The avid birdwatcher, who lives in nearby Bukit Batok, also said she felt that intervention would be necessary only if the mudslides posed a risk to human life.

"I think this (erosion) is part of nature, so we should just let it be as it's not in the path where human beings normally walk."

Environmental consultant Tony O'Dempsey said incidents of soil slippage occur when the soil on a slope becomes saturated with water.

Mr O'Dempsey said: "The lower section of the slope can no longer support the weight of water and soil above and it moves out, the soil above having lost support then moves down.

"The cause is often poor or non-existent drainage at the top of the slope which allows run-off from the water catchment above to cascade over the slope resulting in saturation."

A possible solution, he said, would be to install cut-out drains at the top of the slope where possible.

Chua Chu Kang GRC MP Low Yen Ling noted that this was not the first time the cliff has experienced slope failure.

"We have been keeping a close watch over these areas and have been working closely with the relevant government agencies to help rectify the affected areas and implement safety measures," she told ST.

A footpath along the affected area has been closed since the end of September and NParks has put up signs warning residents about the situation, she added.