Tue, Jul 05, 2011 - Page 2 News List

FEATURE: Shorelines receding due to jetty effect: academics

EROSION:Extreme weather patterns, illegal extraction of riverbed sand and construction of tourism facilities on former windbreaks are also contributing factors

By Liu Li-jen and Lin Yi-chang  /  Staff Reporters

The nation’s shoreline has been eroding over the past three decades, sometimes at a rate of more than 15m per year, academics said.

Numerous fishing wharfs dotting the coastline are the primary cause of shoreline erosion as they have caused a “jetty effect,” said Ling Tsung-yi (林宗儀), an assistant professor of geography at National Taiwan Normal University who was commissioned by the Central Geological Survey to conduct research on changes to the nation’s coastline.

The “jetty effect” refers to hard coastal structures — such as jetties and breakwaters — placed on sedimentary coastlines, which causes erosion of the down-drift shoreline.

The research team conducted the study by overlaying a photo of Taiwan’s shorelines taken in 1978 with a satellite photo taken in 2009, for the first time showing how much the shoreline has receded in 31 years.

A common feature wherever shorelines have receded is that the northern edge of the receded area has dikes perpendicular to the shoreline, which has caused sand to deposit north of the dikes and form beaches, but resulted in erosion to the south, Lin said.

Eroding shorelines have been observed at beaches near the Tatan Power Plant (大潭電廠) in Taoyuan County, the Hsinchu fishing wharf, the Jincheng (金城) and Siangshan (香山) coastlines and Lungfung Port (龍鳳港) in Hsinchu County.

The erosion rate south of the Tatan plant was as high as 6.2m per year.

At the Jincheng to Siangshan areas, the report found that heavy sand extraction from riverbeds in recent years had disrupted the sand balance. The extension of breakwaters at Hsinchu Harbor has cut off sand deposit to the southern shores of the two areas, causing erosion rates at the Jincheng area of up to 15.4m per year, with a total of 500m during the past three decades.

Lin said that stretching the timeline of the study over 30 years clearly showed progressive erosion of the western coastline.

While the eastern shorelines does not exhibit such evident erosion, breakwater reefs erected along the east coast to protect road foundations along Highway No. 11 point to the present danger of shoreline erosion, Lin said.

Statistics from the Council of Agriculture show there are 225 fishing wharfs across the country, with 139 in Taiwan proper.

Compared with the total length of the nation’s coastline, which spans 1,349km, there was roughly one fishing wharf per 9.7km, statistics showed.

Writer and nature enthusiast Liu ko-hsiang (劉克襄) said the density of fishing wharfs and breakwaters in Taiwan is probably a world record.

Green Formosa Front (GFF) said there were multiple factors causing coastline erosion, including changing weather patterns, rising sea levels, blockage and extraction of sand deposits, overpumping of groundwater causing land subsidence and the felling of windbreaks, which has caused sand to be blown inland.

The illegal extraction of riverbed sand and construction of tourism facilities and restaurants on former windbreaks pointed to a failure of land planning policies, GFF acting director Lin Chang-mao (林長茂) said.

The Tatan coastal area once had a thriving and self-sufficient ecosystem and was a breeding ground for sharks and rays, Lin Chang-mao said, adding that after the “jetty effect” began following construction of the power plant, sand deposits covered and killed off vast patches of algae that were a source of food for aquatic species.

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