When Tropical Storm Mindulle crossed the nation on July 2 and caused the Chenyulan River to rise suddenly, Wu Chia-mao (吳佳懋) was very surprised not to hear the roar of rocks being swept downstream.
"In Typhoon Herb in 1996 and Typhoon Toraji in 2001, we always heard the roaring of stones, some weighing one or two tonnes, when the heavy rains came," said Wu, 37, the owner of Shang'an Village's Echin Farm (
Wu has been back in his hometown since 1994 after giving up his job as a radiotherapist at Chang Gung Memorial Hospital in Kaohsiung.
But most of the time since then, it seems, Wu has been fighting natural disasters.
The village, made up of about 500 agricultural families, lies next to where the Sanpukeng Stream flows into the Chenyulan River. But ever since the mid-1990s until recently, the name Shang'an has been synonymous with devastation. The village has been buffeted by mudflows, landslides, river debris, flooding and earthquakes. Grapes grown by persistent farmers on slopes around 450m above sea level are often washed away.
Wu says that after Typhoon Herb in 1996, landslides and mudflows left locals without running water or electricity. For two months they were sustained only by canned food and rice transported to them by air. After the devastating 921 Earthquake in 1999, they were isolated for 40 days. In the summer of 2001, heavy rains brought by Typhoon Toraji claimed more than 17 villagers' lives, destroyed more than 50 buildings and drowned 80 hectares of crops. Survivors ate instant food for a month.
So Shang'an's residents abandoned their crops and houses built in the Sanpukeng Stream danger zone and agreed that government engineers should broaden the river.
The results were encouraging.
"Surprisingly, Mindulle brought no damage to us at all. We just returned the space to the river so it could flow naturally," Wu said.
In two years, engineers with the Soil and Water Conservation Bureau widened the river from 8m to 17m. When Mindulle inundated the area with 760mm of rainfall within three days, the village suffered no flooding or damage from river debris.
According to bureau official Chuang Chih-hong (莊志宏), a comprehensive investigation of the river, which has a 400-hectare catchment area, resulted in the adoption of ecological engineering methods.
One method saw the river's embankment packed with large rocks and stones. According to engineers, such a structure enables the water to press the stones further into the soil, increasing its stability. Another method uses "comb dams" (梳子壩) to block large rocks from rolling downstream without restricting water flow.
"Public safety can be ensured by adopting ecological engineering methods in river-treatment projects," said Kuo Ching-chiang (
On ordinary days, river water flows slowly because dams are built to mediate river steepness. Reducing the angle of the slope generally reduces the velocity of the water running across it.
"Advantages of slow water flow include the replenishing of aquifers, minimizing runoff and reducing the erosion of embankments," Kuo said.
Kuo stressed that other reconstruction projects involving ecological engineering methods proved to be effective in the aftermath of the flooding caused by Mindulle.