Irsyan Hasyim (Contributor), Jakarta – Sedimentologist and former Chairman of the Indonesian Association of Geologists (IAGI), Andang Bachtiar, has addressed the ongoing controversy surrounding sea sand export, a policy reinstated by President Joko "Jokowi" Widodo after a two-decade hiatus.
According to him, large rivers flowing into the South China Sea, including those in Riau, the Gulf of Thailand, Natuna, and northern South Java and Kalimantan, predominantly deposit silt and clay-sized sediments.
These rivers do not contribute significant amounts of sand. Besides, these finer sediments are primarily released during major floods, which occur approximately every 25 years.
In response to widespread criticism, Jokowi stated that the mined and exported sand is sediments that disrupt shipping lanes, instead of sea sand.
Contrary to the president's assertion, Andang maintained that the mined material is indeed sand, not the finer silt and clay deposited by rivers. This sand, he explained, is the essential component for coastal expansion projects, such as those undertaken in Singapore.
The geologist, a graduate of the Bandung Institute of Technology (ITB), emphasized that silt and clay are unsuitable for land reclamation due to their susceptibility to erosion by waves.
He pointed out that the shallow waters of the Sunda Shelf, encompassing the aforementioned regions, are primarily composed of sand deposited by ancient rivers during a period when the area was land.
Andang concluded that the mining of sand in the Sunda Shelf is unrelated to the silting of river mouths. Moreover, he suggested that the ancient river sands may contain valuable minerals, including placer gold and heavy minerals hosting rare earth elements.
Source: https://en.tempo.co/read/1921103/land-reclaimed-from-sea-sediments-could-collapse-due-to-waves-exper