cwlogo

切換側邊選單 切換搜尋選單

Survey of Taiwan's Land Resources

'River of Life' Lost

精華簡文

'River of Life' Lost

Source:CW

Southern Taiwan's landscape has undergone a shocking transformation since being pummeled by Typhoon Morakot last August. What has happened to the land of Taiwan?

'River of Life' Lost

By Rebecca Lin
From CommonWealth Magazine (vol. 442 )

Typhoon Morakot pounded southern Taiwan for three days beginning on Aug. 7, 2009. The catastrophe claimed nearly 700 lives in the region and left more than 10,000 families homeless.

But that was not the end of the disasters preying on Taiwan.

Last week, the strongest earthquake in the Kaohsiung area in a century shook the region recovering from the devastating typhoon. The magnitude 6.4 quake, which struck at a shallow depth of 5 kilometers, terrified Morakot survivors as cracks rippled through houses, and the ceilings in some buildings collapsed. It also rattled their confidence in their ability to live safely and peacefully on this land.

The High-risk Island

From Typhoon Herb in 1996, which inflicted massive agricultural losses, to the Jiji earthquake of Sept. 21, 1999, which took more than 2,400 lives, earthquakes, typhoons, floods and droughts have seemingly taken turns to batter central, eastern, northern and southern Taiwan with almost fatalistic certainty.

In just the last eight months, southern Taiwan has experienced record-breaking rainfall and the strongest earthquake recorded in the area since 1900. "Repeatedly breaking records has become a fact that we have no choice but to accept," says Yang Kuoh-cheng, an associate professor in Providence University's Department of Ecology.

None of this should come as much of a surprise, since the United Nations listed Taiwan as being at high risk from climate change.

"Geologically speaking, no place is safe," warns Meng-long Hsieh, an associate professor in National Taiwan University's Department of Geosciences.

Taiwan's Central Weather Bureau has forecast torrential rains for the second half of March, when spring rains usually arrive. Scholars are warning that the earthquake will only further loosen the soil in areas hit by Typhoon Morakot, and they urged those areas to carefully guard against landslides.

In the face of these mounting risks and the increasing frequency of disasters, do we really understand the fragile land of Taiwan?

An Era of Cataclysmic Change

"We're witnessing the disasters of the past, and also the changes of the land in the future," says Hongey Chen, who like Hsieh teaches in National Taiwan University's Department of Geosciences.

Since the end of last December, a CommonWealth Magazine team has made repeated trips to the Gaoping, Laonong and Cishan river valleys, the epicenters of the disasters spawned by Typhoon Morakot's massive rains. The team found that the land's topography and features had changed to an almost unimaginable degree.

"The Gaoping River has already disappeared. The new Gaoping River has not yet taken shape. The entire path of the river has been buried by landslides. The water, having lost its original broad road, appears as though it has returned to its mother's womb," says brokenhearted poet and physician Tseng Kuei-hai as he stands on a mound of gray gravel, unable to fathom what has happened to the river he has cared for his entire life.

A row of excavators dredging the riverbed seems like nothing more than ants on a boundless beach of sand trying to patch up this stretch of broken land.

"Is there any point to the dredging?" one bystander can't help but ask. 

Typhoon Morakot left in its wake more than 1.2 billion cubic meters of silt – about the volume of 650 Taipei 101 skyscrapers – in a disaster zone spanning Jiayi, Kaohsiung, Pingdong and Taidong counties.

The storm also set off 51,274 hectares of landslides, twice the area of Taipei City and 4.5 times the area of landslides triggered by the massive Jiji earthquake of 1999.

More Terrifying than a Disaster Movie

Sitting in a watershed that covers an area of 3,256 square kilometers, the Gaoping River had once been seen as Greater Kaohsiung's "river of life." But it was nearly transformed into a lifeless "river of greed" because of overdevelopment in its midstream and downstream areas, becoming a haven for illegal gravel digging, garbage disposal and the discharge of wastewater from pig farms.

In 2006, after a 10-year rehabilitation project that included cracking down on illegal gravel operations, relocating pig farms, and burying garbage in landfills, the Gaoping River took on a new look, its glamour once again subtly evident.

But CommonWealth Magazine's long-term monitoring of the river's progress that began in 1996 and the efforts of the government and the people to bring the river back to life were all extinguished overnight.

After the typhoon devastated southern Taiwan, Chi Po-lin, who has been photographing Taiwan from the air for nearly 20 years, rode a helicopter over the Gaoping River basin and suddenly went numb.

"I have never been so badly shaken," he admits. "The change to the land is even more terrifying than what you see in disaster movies. When I watched The Day After Tomorrow or 2012, I felt the scenes were all simulations or special effects. Now, they're playing out before our very eyes," says Chi, recalling the four trips he made to the Gaoping River basin to record the disaster on camera.

The typhoon washed 260 million cubic meters of landslide debris into the Gaoping River, enough to fill two Nanhua Reservoirs. According to the Council of Agriculture's Soil and Water Conservation Bureau, the silt raised riverbed floors by 10 meters to 30 meters, the equivalent of a three- to 10-story building.

"These are not the mountains I know. This is not the river I'm familiar with," laments the clearly shattered Doctor Tseng.

But, do we really know the mountains standing at our side or the rivers flowing by our doorsteps?

NTU's professor Chen led a team of 75 scholars and experts commissioned by the government's Morakot Post-Disaster Reconstruction Council to the river watersheds in the disaster zone to assess the safety of the 144 communities in those areas.

The study of the Gaoping River watershed found that Taiwan's mountains and rivers have some special characteristics:

Geologically Young, with Many Faults

The island of Taiwan is relatively young, having been in existence for only 6 million to 10 million years.

"Taiwan is located at the convergence of the Philippine Sea Plate and the Eurasian Plate. Because Taiwan is young geologically, the plates are still colliding and squeezing against each other. There are rock fractures, and faults are found everywhere," says Chen, who trekked through central Taiwan's mountains and rivers after the Jiji earthquake. 

The earthquake in Jiasian last week struck in the vicinity of the Chaojhou fault, but actually resulted from a hidden fault. Even today, scholars are unable to determine how many of these "undiscovered blind faults" exist in Taiwan, an indication of how much there is still to learn about the country's geology.

Because Taiwan is located in an active seismic belt, there remains considerable tectonic activity, and the process of orogeny that formed the island's mountains long ago through the process of folding the earth's crust continues to this day. 

Sandstone and Shale Leave Taiwan Vulnerable

When there is too much precipitation, the environment's capacity to absorb it becomes overwhelmed.

"That's especially true in the Gaoping River's midstream and downstream areas, where the geological structure is a mix of sandstone, mudstone and shale. The terrain is not only easily loosened and vulnerable to collapse, it features dip slopes and multiple faults and is traversed by a fracture zone, conditions conducive to the entire side of a mountain sliding down," Chen explains. The result was widespread flooding, from the Cishan River Valley, encompassing Namasia Township and Siaolin Village, where hundreds were buried alive during Typhoon Morakot, to the Laonong River Valley, including Liouguei Township and the hot spring resort town of Baolai.

The changing terrain revealed a truth that had never been confronted before – how utterly fragile and sensitive Taiwan's land is. Professor Hsieh of NTU, who has intensively studied the evolution of the country's rivers, does not mince words when describing Taiwan.

"All of Taiwan seems to be a fractured zone. There is almost no place that's safe, especially the Laonong River Valley," he says.

History Repeating

"We found petrified wood deposits to infer when sedimentation occurred. The Laonong River once had a landslide of massive proportions, even bigger than this time," Hsieh says. Compared to other rivers, the Laonong River's topography was rapidly and dramatically changed, leaving the terrain unstable. Considering the area's many previous episodes of turbulence, the recent disaster is only history repeating itself.

But the Laonong River is not an isolated case. Taiwan has always been geologically turbulent. Yao Ying, a scholar from the Qing Dynasty's Tongcheng School, one of the most distinguished of the dynasty's schools of literature, served as an official in Taiwan between 1819 and 1830. He wrote in an article that, "in July of the third year of the Daoguang Emperor (1823), it rained heavily in Taiwan. In Luermen (in present-day Tainan County), deposition from the ocean suddenly formed and became land."

Chang Yi-hsing, the former director of the Water Resources Agency's 6th River Management Office, responsible mostly for rivers in Tainan County, compared present-day maps to ones from earlier times and found that Taijiang Bay, which once separated Luermen from Sigang, was filled in almost overnight.

The Largest Sediment Deposits in the World

During the reign of the Qianlong Emperor (1736-1796), Sinshih Township was still on the coast (of Taijiang Bay), but by 1823, it was described as an inland town. Nobody knows how big the natural disaster was that changed the area's geography or how many lives it claimed, but for it to transform blue sea into green fields meant its scale could have exceeded that of the flooding that followed Typhoon Morakot.

Taiwan's unstable terrain has spawned heavily silted and highly turbid rivers, another of Taiwan's special characteristics. Former Water Resources Agency head Hwang Jing-san, who is now a consultant to the Council of Planning and Economic Development, has studied the problem for much of his life.

"The volume of sediment built up in Taiwan's rivers was the greatest in the world. After the Jiji earthquake, it became the greatest in the universe."

Torrential Rains on the Way

When Taiwan's soft and fragile land collides with climatic extremes, there is always the threat of massive disasters.

Dr. Huei-long Wu, the director general of the Soil and Water Conservation Bureau, estimates that the flooding last August created about 1.2 billion cubic meters of debris in the disaster area that stretched south of Jiayi County and into Taidong County. But only about a third of that, or 400 million cubic meters, actually made its way into rivers, with the rest remaining upstream or at midstream. Thus, the next big storm could trigger even bigger debris flows, Wu believes.

Of the 260 million cubic meters of debris washed into the Gaoping River, only about 1 million cubic meters, or less than 1 percent of the total, has been delivered to the river's estuary.

Only two months remain before the rainy season begins in May, which has at least one expert worried.

"We're in a race against time," declares Jenn-chuan Chern, the deputy CEO of the Morakot Post-disaster Reconstruction Council and a civil engineering expert. He says the government must complete the resettlement process and some reconstruction projects before the flood season begins, to prevent villages along riverbanks from suffering more devastation.

"Disasters will definitely come. We just have to mitigate the loss of life and property as much as possible. We can't obstinately fight nature. We simply don't have the ability to do that," Chern says.

Rainfall to Increase at an Alarming Rate

Taiwan has long been considered a high-risk island and recent scientific studies tend to confirm that.

Wang Chung-ho, a research fellow in Academia Sinica's Institute of Earth Sciences, pulled out a United Nations report that listed Taiwan among the 10 countries that would be most seriously affected if sea levels were to rise by one meter.

"For every one degree Celsius that the Earth's temperature rises, rainfall increases by 6 percent. But because of Taiwan's topography and other geographic factors, the rate of increase in the precipitation it receives will be five times the world average," he says.

Floods? Or Drought?

Not far from the Liling Bridge in Pingdong County, where the Laonong, Cishan and the Ailiao rivers converge into the Gaoping River, an island of gravel was buried by fine sand overnight. Now when strong northeasterly winds blow in, they spread the sand everywhere, leaving residents thinking they are in the middle of a desert.

Silt accumulating downstream also poses a threat to the Gaoping River's weir, built to capture water to be supplied to nearby areas. The manager of Taiwan Water Corporation's Kaohsiung's water plant, Ruan Tung-lung, said rainfall is normally limited during the dry season, but this year there is even less precipitation than normal. Exacerbating the problem is that when water flows down from the mountains, not only is it quickly absorbed by the built-up silt, but also the river's zigzagging path accelerates evaporation.

When a fragile land meets a repeated onslaught of violent storms, what can Taiwan's people do to rehabilitate the rivers on their doorsteps and the mountains that rise at their backs?

Transalted from the Chinese by Luke Sabatier

Keywords:

好友人數