Mon, Apr 08, 2002 page4

• Reservoirs shrinking as silt deposits grow

  FLATTENING OUT Soil erosion and deforestation have caused tonnes of sediment to end up in the nation's dams while public officials have neglected to clean it out

  • By Chiu Yu-Tzu / STAFF REPORTER
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  Legislators warned last week that Taiwan's reservoirs have accumulated too much silt and are losing their capacity to hold water.

  Long-term soil erosion caused by poor land management in mountainous areas has brought tonnes of silt down into the nation's dams. Recent statistics show that 277 million cubic meters of silt have accumulated in Taiwan's reservoirs. However, by the end of last year, only 29.7 million cubic meters of silt had been removed.

  Sedimentation has reduced the effective storage capacity of 40 reservoirs in Taiwan from 2.324 billion cubic meters to 2.047 billion cubic meters. Storage capacity is reduced 11.32 million cubic meters per year due to the accumulation of sediment.

  

  Low water-levels caused by a mild drought have made it easier to dredge silt from the bottom of Taiwan's dams.

  PHOTO: CHU YU-PIN, TAIPEI TIMES

  "The situation can be attributed to the shortage of funds for carrying out sediment dredging projects," Hwang Jing-san (黃金山), director-general of the newly-formed Water Resources Agency (WRA, 水利署), said at the Legislative Yuan last Thursday.

  Hwang's statement came in answer to questions raised by PFP Legislator Pang Chien-kuo (龐建國) and KMT Legislator Chen Chieh (陳杰). Legislators questioned water resources officials about the build-up of silt in the reservoirs and demanded that emergency measures be implemented to dredge sediment from the nation's reservoirs.

  Water resource officials said that the agency is currently conducting two sediment dredging projects but the projects may not be completed due to a lack of funds.

  According to the agency, the cost of digging out a cubic meter of sediment during the dry season is less than NT$200, while removing silt by dredging costs around NT$500 per cubic meter. If the sediment is transferred to public dumps, operated by the Construction and Planning Administration (營建署, CPA), the storage of a cubic meter would cost NT$1,000.

  To reduce the cost of handling sediment, water resource officials say they have negotiated with the Environmental Protection Administration (EPA) to build two coastal stations where sediment could be dumped directly into the sea. Officials say that dumping sediment into the sea would cost less than NT$100. The EPA, however, is still evaluating both the ecological and environmental impact of sea-dumping.

  "The loss of reservoir capacity should have attracted more attention in Taiwan. The EPA and the CPA as well as other Cabinet agencies should cooperate on a sediment removal project. This should also be discussed by the legislature," Pang told the Taipei Times.

  Reasons for incompetence

  A water resource official, who declined to be identified, told the Taipei Times that the negligence could be attributed to the lack of dumping sites for sediment.

  "Before a market mechanism is established, handling sediment dredged out from reservoirs will still be a headache," the source said.

  The capacity of Taiwan's reservoirs has been reduced due to the government's wait-and-see attitude toward sediment problems. Water storage capacity problems have caused serious flooding at many places in Taiwan.

  In August 1994, Kangshan township (岡山), Kaohsiung County suffered from a rare flood due to A-Kung-Ten Reservoir's (阿公店水庫) inability to hold all the water that flowed into the dam.

  Records showed at the time that about one-tenth of the water overflowed.

  The reservoir, one of the biggest dams in southern Taiwan, was completed in 1952 with a storage capacity of 20.5 million cubic meters. Because of environmental deterioration, the reservoir on average absorbs 0.5 million cubic meters of silt a year. Currently, less than 30 percent of its original storage capacity is available.

  An eight-year renovation project costing NT$8 billion was eventually started at the reservoir in 1998. The ambitious project aims to remove 11.6 million cubic meters of sediment. Officials said that, after the renovation, the capacity would be increased to 19.16 million cubic meters from the current 5.9 million cubic meters.

  Problems pertaining to significant reductions in storage capacity caused by sedimentation are also faced by reservoirs in the rest of the world. Last December, the United Nations Environment Program (UNEP) warned that, on average, 1 percent of the water storage capacity of the globe's reservoirs is being lost annually because of a build-up of silt.

  According to the UNEP, the current storage capacity of reservoirs worldwide is estimated at just under 7,000km3. Unless urgent action is taken, a fifth of this or some 1,500km3, will be gradually lost over the coming decades.

  "Making more efforts to reduce the loss of forests and to reforest exposed areas should be part of a comprehensive strategy to managing water resources," legislator Pang said.

  Premier Yu Shyi-kun last Thursday said he was in favor of building 700 hectare Ji-Yang artificial lake (吉洋人工湖) when he inspected Meinung township (美濃), Kaohsiung County. Yu said that lake was an alternative to a plan to build Meinung Dam (美濃水庫), which might cause environmental deterioration.

  Controversies surrounding the Meinung Dam project have cooled down since July 2000, when President Chen Shui-bian (陳水扁) promised that the dam would not be built during his presidency.

  Anti-dam activists, however, said that building new dams to solve water shortage problems without doing dredging first is irresponsible. In addition to reducing the lifespan of existing dams, activists said, sediment creates problems during dam removal.

  "Sooner or later, water resource officials have to face sedimentation problems as water demands increase," Chang Cheng-yang (張正揚), an activist from the Meinung People's Association (美濃愛鄉協進會), told the Taipei Times.

  Water resource officials said that a five-year project, costing NT$2 billion and beginning this year, would eventually remove 6.28 million cubic meters of silt from 13 dysfunctional dams, upon which millions of residents depend for drinking water and for irrigation use.

  Tomorrow, water resource officials are supposed to come up with strategies to remove at least one million cubic meters of silt from six major dams by the end of this year, including Shihmen Dam in Taoyuan County, a major dam in northern Taiwan.

  In early March, emergency measures involving a fallow project and water limitation in northern Taiwan were implemented to make up for the shortage of water at the Hsinchu Science-based Industrial Park (新竹科學園區).
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