River curvature in Taiwan ranks second in North Pacific

The sinuosity of Zhuokou River, an upstream tributary of the Laonong River in southern Taiwan's Kaohsiung County, is even higher than that of rivers in Luzon, said Hongey Chen, a professor in National Taiwan University's (NTU) Department of Geosciences and an expert on Taiwan's river systems.

Rivers in the southern Japanese island of Kyushu are also very sinuous because of typhoons, Chen said at a news conference.

The findings were made by an international research team that studied the impact of the climate and geological environment on the sinuosity of rivers — the extent to which they bend or curve — in Japan, Taiwan, the Philippines, Borneo and Papua New Guinea, Chen said.

The research results are published in the latest issue of the prestigious journal Science.

The research team was composed of scholars mainly from the United States, Britain, Japan and Taiwan.

Colin P. Stark, a professor of Columbia University in New York City who was the leading author of the article, was in Taipei to unveil the study's results along with Chen at a news conference Friday. NTU President Lee Si chen and the school's other senior administrators were also present.

Stark said that while climate controls landscape evolution, quantitative signatures of climatic drivers have yet to be found in topography on a broad scale.

The newly published paper describes “how a topographic signature of typhoon rainfall is recorded in the meandering of incising mountain rivers in the five western North Pacific islands.”

The study found that “the weakness of bedrock channel walls and their weakening by heavy rainfall together modulate rates of meander propagation and sinuosity development in incising rivers.”

Given the strong impact of heavy rainfall on rock stratums, Stark said land developers and planners should not ignore the weakening trends of bedrock channel walls.

Meanwhile, Chen said rivers in areas between latitudes of 8 degrees and 25 degrees are most sinuous because of their relatively high typhoon frequency.

Noting that southern Taiwan's rock formation has become much weakers after Typhoon Morakot, Chen said the government should conduct a thorough survey of low-lying river stretches in southern Taiwan out of safety concerns.

He further said special precautionary measures should be taken in the upper stretches of five extremely sinuous rivers — Ailiao North River, Er-ren River, Chenyulan River, Tsengwen River and Alishan River — during the typhoon season.

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