New Use for Old Wisdom--Underground River Weirs

At the beginning of January, when southern Taiwan is entering the dry season and the gravel of the riverbed is visible, this reporter visits the entrance to this underground corridor on the Linpien River. As soon as the door is opened I am met by the sound of rushing water coming up from the shadowy depths. It makes a stark contrast with the dry riverbed outside. Professor Ting Cheh-shyh of National Pingtung University of Science and Technology's Department of Civil Engineering climbs down a rusty iron ladder to check the water and finds it knee-deep and flowing very fast. He suggests I don't come down.

"This construction, buried three meters beneath the riverbed and 1.8 meters high, originally was not supposed to be visible," says Professor Ting. He points to a stairway in the middle of the riverbed. This was originally the top of the underground weir. Because the Linpien River gravel was over-mined and the riverbed thus lowered, this area is now exposed.

As I stand on the riverbank, the structure of the underground weir becomes immediately apparent as I compare it with the cross-section diagram. (See diagram.) The steps of the weir embankment are studded with concrete pillars that stick out at an oblique angle and form a square enclosure for collecting water. The groundwater infiltrates the water corridor between the concrete pillars. Because three sides of the corridor are walls that do not allow water to pass through, part of the groundwater beneath the riverbed flows into the corridor, which is more than 200 meters long, and then follows a ditch 3.4 kilometers long to the water intake area. Because the route is through varied topography, the water may sometimes be exposed as it flows along at the foot of the mountain and then once more will enter the tunnel.

During the dry season the Linpien River bed is dry, but water in the Twin Peak Ditch that lies deep underground flows freely. This age-old method of obtaining groundwater has gradually won the recognition of modern-day experts.

A masterpiece

At the beginning of the Japanese occupation period, under the policy of "agricultural Taiwan, industrial Japan," the Japanese government planned to grow rice and sugar cane on the Pingtung Plain but was hindered by the highly unstable surface hydrology. During rainy seasons there were often floods, and during dry seasons there was not a drop of water to be found. Japanese hydraulic engineer Shinpei Torii skillfully designed an underground water project to utilize the plentiful groundwater here.

"In the beginning they were only able to use simple manpower and crude machinery, taking two years to finish the job," says Ting Cheh-shyh. After the underground weir was finished in 1923 there was a daily output of 250,000 tons of water during the rainy season and 80,000 tons during the dry season, irrigating 2,500 hectares of farmland. Today, although there have been no repairs made over all these years, it still provides local farmers an average of 30 million tons of water a year (an average of more than 80,000 tons a day).

Ting Cheh-shyh says there is another underground weir on the upper reaches of the Lili River in Pingtung that is still providing water. Because of the ingenious design of these underground water projects they have very little negative impact on the environment, and Professor Ting has a great deal of admiration for them. In recent years these projects have begun to draw the attention of academics and specialists. He says that if similar underground weirs were built along some areas of the the Chingshui River, a branch of the Choshui River, and the Ailiao River on the Pingtung Plain, they could provide a daily water output of 500,000 tons, almost equal to the capacity of the Shihmen Reservoir-a very considerable amount.

Following the Twin Peak Ditch along the foot of the mountain and snaking its way down to the Aboriginal village of Laiyi, the gurgling water in the channel emerges from the tunnel, and butterflies dance around the grasses that reach out from between the cracks in the rocks on the sides of the "ditch." Ting Cheh-shyh is very much looking forward to a near future where this old wisdom will shine brightly once more.