Sat, Aug 13, 2005 page8

• Water woes demand creative fixes

  • By Lee Ken-cheng 李振政
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  The turbidity of the water in the Shihmen Reservoir (石門水庫) has worsened to 25,000 NTU (nephelometric turbidity units). The poor water quality has left more than 630,000 households in both northern and southern Taoyuan County either receiving water on a rotational basis or not at all.

  The recent water supply problem in Taoyuan County came in the wake of Typhoon Matsa on Aug. 5, and it was a recurrence of the problems caused by Typhoon Mindulle last July.

  Also, flash floods bringing turbid water into the Touchien River (頭前溪) in Hsinchu County caused a nearby water purification plant to shut down and left an additional 50,000 households in Hsinchu County without running water.

  By the same token, certain cities and counties in the south, such as Kaohsiung and Pingtung, are facing similar problems. But the public has a short memory for such problems.

  After a prolonged drought last month and this one, southern Taiwan was looking forward to rain showers to relieve the drought.

  Unfortunately, what came after were the devastations of the June 12 flooding and Typhoon Haitang on July 18.

  The turbidity of water in the Kaoping River (高屏溪) reached 27,000 NTU at one stage, greatly surpassing the upper limit of 5,000 NTU for purification to be effective.

  The turbidity of the off-stream Nanhua Reservoir (南化水庫) in Tainan County also reached 7,400 NTU at one point. This caused approximately 530,000 households in Tainan, Kaohsiung and Pingtung to be without running water.

  Despite the Taiwan Water Corp's (TWC) all-out efforts to restore the water supply at an early date, hundreds of residents in Kaohsiung City's Tsuiping Borough recently had their water cut off for as long as seven days.

  TWC officials have already announced that water shortages will be a recurring problem in Taoyuan because of a high water turbidity level resulting from typhoons and torrential rains.

  The Pingting Water Treatment Plant (坪頂淨水廠) recently treated about 453,600 tonnes of water each day.

  It was found that the silt content was between 45,360 tonnes to 90,718 tonnes a day, accounting for one-fifth of the total volume.

  How could such turbid water be used? Would building more sedimentation tanks be of any help?

  About 80 years ago during the Japanese period, a Japanese engineer used hydraulic engineering techniques to construct the Erfeng Ditch (二峰圳), and since then, the water in the Linpien River (林邊溪) has remained clear all year around.

  The thinking behind the construction of the ditch in the region originated from the recurring flooding and drought problems in areas near the Taiwan Sugar Corp's Wanlung Farm (萬隆農場).

  The Erfeng Ditch, an underground water intake structure, was built at the headwater of the Linpien River, which is currently located 100m upstream of the Laiyi Bridge (來義大橋) in Pingtung County.

  The construction of the Erfeng Ditch was completed within two years, and its water intake structures include four different parts: trapezoid water diversion weirs, semi-circle underground watersheds, arched channels, and water-gathering towers.

  The complex constructions cannot be seen above ground since they are under the riverbed.

  During the first decade after the completion of the Erfeng Ditch, the water supply was as much as 228,610 tonnes during the rainy season.

  Although the ditch was partially damaged, its water supply can still reach 74,390 tonnes per day, an amount higher than the Ahgungtien Reservoir (阿公店水庫) or the Paiho Reservoir (白河水庫).

  Basically, the Erfeng Ditch is an underground water diversion weir under the riverbed.

  Since surface water goes through permeable sand and gravel as a natural filtration process, even during periods of heavy rainfalls or typhoons causing high water turbidity, the Erfeng Ditch can still have supply clear water.

  Faced with the long-term failure to reduce the turbidity of the water supply during periods of heavy rainfall, the government should reflect on the reason why even after a large expenditure of money on large-scale hydraulic engineering projects, such as constructions of dams and water diversion weirs, the water shortages remain a recurring problem.

  There are two other possibilities to help gather clean water: building the Kaotai Reservoir (高台水庫) at the upstream watershed of the Shihmen Reservoir or implementing transbasin diversion -- the diversion of water from one water division for use in another water division -- at the Tsengwen Reservoir (曾文水庫) on the Laonung River (荖濃溪)?

  But would these two projects simply be high-investment projects that yield low returns?

  My purpose in this article is not to praise the successful hydraulic techniques used in constructing the Erfeng Ditch.

  Instead, I want to use the Erfeng Ditch as a reminder that if the water turbidity problems after heavy rain continue, the government's stubborn belief in the construction of weirs and dams should be discarded.

  Instead, the government should find a way for effective water resource management that can truly benefit the nation.

  Also, it would probably be a way to stop future water stoppages during the rainy season.

  Lee Ken-cheng is the chief of the Kaohsiung Teachers Association's Ecological Education Center.

  TRANSLATED BY LIN YA-TI
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