Land subsidence used to be a problem that was mostly confined to coastal areas. But over the past decade, inland land subsidence has become a major issue, particularly in Yunlin and Changhua counties. This phenomenon not only threatens the safety of the high-speed rail but also indicates a more sinister danger pertaining to local groundwater tables and agriculture. At Yunlin’s Tuku Township, National Cheng Kung University is working with the Water Resources Agency to develop a land subsidence prevention group. Changes to magnetic rings in monitoring wells identify the degree of land subsidence.Chen Chien-mingCivil EngineerLand subsidence affects entire areas. This makes it difficult to figure out the degree of subsidence of a particular location.A decade ago, an FTV episode of “Hall of Dissent” addressed the issue of coastal land subsidence. During the course of the investigation, one local expert said the same problems could occur inland. Liu Chih-hsiITRI Environmental Research LabNew monitoring data shows that the Yunlin area is experiencing subsidence due to pumping. The long-term, slow nature of subsidence means that few people can actually feel it.Though it’s difficult to see, Yunlin’s Tuku and Huwei Townships as well as Changhua’s Xizhou and Xihu are experiencing subsidence which is more serious than coastal regions.Chen Ching-jhenTaiwan Academy of Ecology Over the past few years, torrential rains in Dounan, Huwei and Tuku left these areas flooded with water up to 1 or 2 meters deep. Chen Chien-mingCivil EngineerInland subsidence can be detected by post-rain water accumulation in areas that didn’t use to have stagnant water. Now we are seeing water accumulation in more places.In the past 15 years, Yunlin and Changhua have seen subsidence reaching up to 2 meters. This could cause more flooding concerns. Lee Hong-yuanNTU Civil Engineering Dept.In Taiwan today, rice barns can seen from Changhua, Yunlin and Chiayi to Pingtung. These are the areas where land subsidence is taking place. Climate change has already led this soil to experience some degree of salinization, but excessive groundwater pumping is exacerbating this problem. If we continue to pursue this route, in another 10 to 20 years we won’t be able to grow these crops.It’s hard to believe that the subsidence problem doesn’t have anything to do with the 1,200 wells in Yunlin and Changhua.Lee Hong-yuanNTU Civil Engineering Dept.Who owns some of the deep wells? They belong to the Taiwan Water Company, the Water Resources Agency, Taiwan Sugar, schools, prisons and factories.Lai Chien-hsinWater Resources AgencyIn the past, we found there were approximately 1,200 deep wells. Over the last several years, some 30 to 40 percent have been sealed.Beginning in 2011, the government began to seal deep wells in Yunlin and Chiayi, including some 350 owned by the water company.Hsu Ruei-ming Taiwan Water Corp.To cooperate with groundwater management for the area we sealed this well. If we face a drought and experience third-stage water restrictions with insufficient water supply then we can make a report to the Water Resources Agency and open the well again.These 350 wells extract 150 million tons of water each year to supply households and industries. If they are sealed, many fear there will be no water for household use. Lai Chien-hsin Water Resources AgencyOriginally, in the Changhua and Yunlin area, a high percentage of people relied on groundwater for tap supplies. But now we are changing to cleaner water supplies, such as Hushan Reservoir or the newly completed Niaozueitan Artificial Lake. Hushan will mainly supply Yunlin while Niaozueitan will supply Changhua. Surface water will be able to supply tap water in the two counties.Some wonder if sealing off these wells can really stop land subsidence. Along the Yunlin and Changhua high-speed rail route there are some 310,000 private wells mainly used by farmers to irrigate rice fields.Liao Ming-chinFarmerNearly half of the 120 days during the first rice planting require water. Since I plant soy beans, I only need to irrigate four times.Beginning in 2014, the Council of Agriculture told farmers to convert to crops that can be grown in dry fields where severe subsidence was a problem.Liao Ming-chinFarmer(Soy bean income) is relatively good because we use organic growing methods. Our costs are higher and we work a little more, but prices are good. There are also subsidies for having converted crops, for organic farming and to purchase organic fertilizers.Though the government may be doing what it can to solve this problem, some believe it isn’t doing enough.Chen Ching-chenTaiwan Ecological Research Center Now our problem is that industrial zones are expanding. The combination of new industrial zones and traditional industrial zones is creating high demand for water.Lee Hong-yuanNTU Civil Engineering Dept.The Ministr...

• published: 31 Aug 2015
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