Mountain MendingBioengineering Limits Post-Quake Erosion

In the wake of Typhoon Toraji, a creek bed in the Peikang area of Chilin in Puli Township has greatly widened, and the collapsing banks bode ill for nearby chicken coops and residences. The whole area is suffused with a stench. "This is first great 'clearance sale' of the soil and rocks loosened by the 921 earthquake," says a frustrated Tung Chuan-fa, who heads the agricultural economics department for the Puli government.

Just three kilometers from Peikang there is a 1.2 hectare site with a nearly 90o slope that was the site of a severe collapse during the 921 earthquake. Now, however, it is covered with lush greenery. Chinese crape myrtle (Lagerstroemia subcostata) shoots are everywhere the eye turns. Nothing here would suggest potential for landslides, and the houses at the bottom of the slope are in good shape. Shen Kuo-yi, head of recovery engineering for Puli, says, "Can you believe that it looks like this just two weeks after Typhoon Toraji?!"

The bioengineering at Chunghsing Ling has been completed little more than a year, but already tree saplings are beginning to take hold. These slopes stand in sharp contrast to the barren slopes adjacent to them, which are constantly being eroded by rain.

Likewise, the Wuhokang Creek in Hoping, Taichung County, suffered no erosion at all from the 400 millimeters of rain that Toraji dumped on it. Results such as these are the best possible advertisement for bioengineering erosion control.

As a result of the 921 quake and heavy rains, woodlands along the banks of the Wushihkang Creek collapsed, causing a loss of more than 500 hectares of watershed. The 15 check dams along Wushihkang Creek could only hold back one-fifteenth of what they could before the quake, and the new ones put in place after the quake turned out to be nearly useless, silting up as soon as it rained. In that state, Wushihkang Creek represented a serious danger during the typhoon season. The Post-Disaster Recovery Commission, therefore, carried out intensive erosion prevention efforts in February of this year in Forest Sector 1220 along the banks of Wushihkang Creek. Locals have taken to calling the project the "Little Great Wall." Work on the first stage was completed in just two months. When Typhoon Toraji arrived just months later, it caused some mild reshaping of the wattle fencing laid to support the growth of vegetation over erosion gullies, but no landslides. These excellent results have caused the Post-Disaster Recovery Commission to strengthen its promotion of bio-engineering erosion control.

On the slopes above the Shantien Temple in Puli, bioengineering workers are installing live wattle fences and safety nets. They say proudly, "We want to save the land beneath our feet!"

What exactly is bioengineering erosion control? Simply put, it refers to human efforts to restore the natural balance in areas that have suffered from serious erosion.

Dr. Chin Kuo, deputy executive officer of the Post-Disaster Recovery Commission, drew up the basic guidelines for implementing bioengineering in Taiwan. In order to fully restore areas where the ground was dangerously loose, he scurried around the island, visiting nearly all of the areas damaged by the 921 quake. In the course of his fieldwork he discovered the same problems almost everywhere: damaged forests and shattered, loose rock that wouldn't hold together in heavy rains. Past solutions, such as building check dams and levees, were both overly expensive and too limited in their effect to address the severity of the situation after the 921 quake. So Kuo called together a group of distinguished academics, including Chen Su-chin, a professor of soil and water conservation at National Chunghsing University; Hsieh Cheng-lun, a professor at the Disaster Prevention Research Center at National Cheng Kung University; and Debbie Weng, president of the Taiwan Soil and Water Conservation Professional Engineers' Association. Combining theory with practice, they came up with a set of ecologically based principles for erosion prevention bioengineering. These methods made use of local materials and tried to tackle the problem of erosion at its roots.

"If you want to prevent landslides by removing the cause for erosion, which is simply water meeting soil, then you've got to get the water to flow elsewhere-toward vegetation," explains Kuo. "That will prevent future erosion." This new strategy represents a great departure from past efforts to build levees in lower stretches of rivers and revetments at mid-stream locations. Instead, by stressing protection of upstream vegetation in the watersheds, it offers an overall vision for erosion prevention. This general vision includes keeping watershed hillsides free from erosion gullies and mending slopes and embankments that have collapsed due to flooding. It also entails the management of accumulation zones at the base of the slopes and preserving channel flows in sedimentation areas.

Prevention work in the watersheds is the most important task, explains Chin Kuo. The 921 quake left open gashes on the face of many mountains in central Taiwan. Whenever there was heavy rain, the exposed soil and rocks would flow downstream. In accordance with bioengineering principles, the erosion control teams looked for and filled erosion gullies near the mountaintops and ridgelines. This methodology also calls for cutting off and redirecting water flow away from filled erosion gullies. For this reason, humus-rich soil cannot be used to fill them. Moreover, the work of filling the gullies must be done manually, one layer at a time, to ensure that all the cracks and crevices get well packed.

Vegetation is introduced on exposed slopes. Live wattle fences-"live" because the wattle is living wood that can take root and draw shoots-are used in a manner fitting the steepness of the slope. Vegetation is introduced to increase slope stability and help the land make a complete recovery as soon as possible. Meanwhile, live gully breaks and live pole drains are employed to direct surface water to places where there is vegetation. The first plants on the formerly naked slopes are fast-growing cover plants such as Bahia grass. Sun-loving trees and bushes and then shade-loving trees and bushes follow. The eventual result is a complex, multi-layered ecosystem.

In sedimentation zones at the foot of mountains, the land recovery teams make further use of wattle fences and live water breaks and drains, and they take measures to ensure the stability of the sedimentation base. They also make plantings to ensure the stability of slopes.

Downstream the teams first assess the dimensions of the channels needed based on the watershed area and the potential rainfall there. They also dredge channels for sediment to increase floodwater capacity and employ local materials to strengthen embankments and stabilize the beds of rivers and streams. Plantings are made all along the banks to prevent erosion and create a buffer zone of vegetation.

The implementation of bioengineering erosion control also makes the most of local talent. This is done both to help the team gain familiarity with the local environment and to provide the locals with opportunities to work. The silver-haired and gentlemanly Chin Kuo says straight out that jobs are scarce in the areas that were hit hard by the quake. "Once there was a fellow who pointed to a small truck and said, 'Mr. Director, that's all I own.'" By hiring unemployed locals Kuo hopes that "the opportunity to work will restore their confidence and concern for the land."

The first phase of bioengineering work took place from February 1 to May 31 of this year, when teams carried out the urgent work of finding erosion gullies and dealing with them before the season of typhoon rains. Over these four months, government-sponsored bioengineering projects employed a total of 2,500 people and spent more than NT$370 million. The township governments in the reconstruction zones were responsible for hiring and organizing workers, ordering materials and the like. They were putting on training seminars at the same time as they were starting work in the field. The Council of Agriculture's Soil and Water Conservation Bureau offered workers NT$1,500 per day to join the teams in the field, and they encouraged locals to apply. At a moment's notice 60 year-old grandpas, painters, hospital volunteers and unemployed youths were out together rebuilding the land. They went from a state of complete ignorance about bioengineering methods to looking for potential erosion on their own initiative. The success of the project gave them all tremendous confidence.

The bioengineering at Chunghsing Ling has been completed little more than a year, but already tree saplings are beginning to take hold. These slopes stand in sharp contrast to the barren slopes adjacent to them, which are constantly being eroded by rain.

Tung Chuan-fa, the Puli government official who was in charge of the bioengineering efforts there, relates that he has started on his own to regularly check the hillsides behind his home. He's even made plantings and built structures to guide the water flow. "Now there are zero signs of collapse in the hills behind us!"

Lin Wen-sheng, mayor of Hoping Rural Township, says that townspeople were so worried that the typhoon might have damaged the erosion control works they had built themselves that they ran out the day after the typhoon to check for damage. They also regularly check for any loosening of the soil on the slopes. "When natural disasters happened in the past, the youths in the village would just stand off to the side and wait for the military to help. Now, with confidence in their abilities, they act on their own initiative!"

Chin Kuo explains that the three towns where the erosion control efforts were most intensive-Kukeng, Puli and Chungliao-were the places that suffered least from Toraji's rains. But he makes a point of reminding people that finding erosion gullies is the biggest obstacle facing bioengineering efforts. This is because the gullies are often in remote wilderness areas, and are particularly hard to find in the spring and summer when the grass is high. "If hikers and farmers can keep an eye out for erosion gullies and then immediately fill them, that would be a huge step toward solving the problem." What's more, construction of roads and bridges is a major cause of erosion, and therefore should be avoided if at all possible.

(left) Vertical channels in slopes are aimed at providing an exit for water. This channel has been covered in non-woven fabric so that water won't further erode its bed. The fabric, which covers the entire channel, also protects the grasses and trees from being swept away by flood waters.

Cheng Meng-ta, who was a member of an erosion repair team in the mountains after the 921 earthquake, paraphrases an old expression about fengshui. "For ten years it runs west, for ten years east," he says. "This time the river is running its true course!" Debbie Weng says, "The experience of people in Taiwan with natural disasters is like that old proverb: 'Though my ligaments are torn and my bones are broken, I'm stronger than ever.' Only if people develop consciousness about natural disasters fast enough will erosion control efforts really prove to be effective!"

Huang Jong-tsun, executive director of the 921 Earthquake Post-Disaster Recovery Commission, puts it thus: "The meaning of the phrase 'live not in lands of danger' has become all too clear after the quake. The experience of living through a natural disaster together, moreover, has caused people to help each other and value others' good deeds. It has also caused many to experience first-hand the moving power of 'baptism by fire.' Now we've become like Israel, a nation highly conscious of how to respond to crisis and disaster!" Let us hope the people of Taiwan will treasure this collective experience and find a way to live in harmony with the land-for only through recovery can Taiwan become whole again!

Yufeng Village in Shuili Rural Township suffered a horrific rockslide.

The bioengineering at Chunghsing Ling has been completed little more than a year, but already tree saplings are beginning to take hold. These slopes stand in sharp contrast to the barren slopes adjacent to them, which are constantly being eroded by rain.