Scientists Study River Shifts

The tentacled figure on the screen in the darkened hotel ballroom—a map of the river junction at Phnom Penh—stretched, narrowed, then widened a bit as it shifted through a kaleidoscope of colors.

What was being displayed Wednesday at the seminar at Hotel Le Royal was a sped-up model of the evolution of the junction since 1876. It was a dramatic illustration of how objects that seem to be permanent fixtures—the course and depth of a river, the shape of a peninsula—can change dramatically even over the course of a human lifetime.

In fact, the Mekong River Commis­sion says the entrance to the Bassac River has migrated 1,240 meters south since 1876. The Chroy Changvar peninsula, across from the Royal Palace, has moved 715 meters south.

The causes of the shift are largely natural, as the Mekong River has meandered southward and the Bassac has moved westward, engineers at the seminar said. But with settlements and new developments right on the riverbank, careful planning is necessary to avoid damage to homes and livelihoods.

“A wrong decision in the Chak­tomuk area can have disastrous consequences,” said Khy Tangliem, chair of the Cambodia National Mekong Committee.

Seminar participants from Cambodia, Thailand, Laos and Vietnam discussed a Japan-funded Mekong River Commission study on how to stabilize riverbanks in the Chaktomuk area. Since city-sponsored work has already begun to build flood protection embankments on Chroy Changvar peninsula and fill in new land along the Bassac River south of the Royal Palace, the study also suggests ways to make those projects sustainable.

Engineer Ranjit Galappatti said the city’s plan would not solve the problem of a skewed alignment at the entrance to the Bassac. The misalignment leads to rapid erosion on the Bassac’s east side near the river entrance, he said.

The Mekong River Commis­sion has recommended an additional $7 million in dike and embankment construction and channel dredging to stabilize the entrance to the Bassac.

Galappatti said other forces could change the river’s alignment. Between 200,000 and 500,000 cubic meters of sand are mined from the Chaktomuk area each year, the commission estimates, which could lead to a severe erosion problem in coming decades.

 

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