The distress call rang out at 12:42am on Aug. 9, a desperate cry for help from 31-year-old Tsai Ya-hsueh (蔡雅雪) to her sister after her car plunged off Shuangyuan Bridge (雙園大橋) crossing the Gaoping River (高屏溪) and into the abutment of the bridge.
“The bridge is out! I have fallen in ... Come save me! Hurry,” she said on the telephone.
Tsai’s mobile phone signal soon died, however, in the rampaging waters fed by Typhoon Morakot, and she became one of the storm’s early casualties.
Similar tragedies played out on roads and bridges around central and southern regions, focusing the spotlight on the country’s traditionally vulnerable bridges that often collapse during natural disasters.
What was different this time was the scale and severity of the destruction, especially in Pingtung, Kaohsiung, Chiayi and Nantou counties, and the questions this raises about how bridges in Taiwan will be built and managed in the future.
As of noon on Wednesday, a total of 90 bridges around the nation had collapsed, with another nine requiring repairs to abutments, said Yao Nai-jia (姚乃嘉), head of National Central University’s Center for Bridge Engineering Research, who has been monitoring the situation with government officials.
That number, he said, still did not include bridges on the Southern Cross Island Highway (Highway 20) that may have collapsed in areas that remain inaccessible.
“Never before has a single typhoon caused bridge damage on such a massive scale,” said Lin Chia-hsin, a Directorate-General of Highways (DGH) official in charge of highway and bridge maintenance.
Particularly worrisome to officials is the fact that only three of the 14 major bridges that collapsed on nationally administered roads — the Tajin Bridge (大津橋), the Liouguei Bridge (六龜大橋) and the Ciwei Bridge (旗尾橋), all in Kaohsiung County — were listed as “dangerous” following a countrywide inspection last year.
Bridges such as the New Ciwei Bridge (新旗尾橋) and the No. 1 Bridge (一號橋) that were pronounced “structurally sound with no serious problems” in last year’s assessment also fell victim to Morakot’s raging floodwaters.
Highway officials and bridge engineers generally agree that the staggering amount of rainfall dumped by Morakot over a very short period — 2.5m of precipitation, or a year’s rain in three days — was the main culprit behind the high number of bridges destroyed.
Given more extreme weather patterns caused by climate change, massive storms such as Morakot could become more common in the future.
Academics said that with this in mind, the government should update bridge management procedures, including revising criteria for closing bridges in stormy weather.
Water levels have traditionally been the sole criteria for bridge closure amid flooding. This time around, many bridges were not closed before they collapsed.
Take, for instance, the 2,083m Shuangyuan Bridge, which was actually two separate bridges, one for each direction of traffic.
The water level in the Gaoping River was still 4.5m lower than the riverbank when the northbound bridge’s No. 1 and No. 15 piers, and the southbound bridge’s No. 1 and No. 16 piers were washed away by the currents.
Under current guidelines, bridges do not need to be closed off until the water level rises to within 1.5m of the riverbank’s upper level.
“The rules should be overhauled and should take into consideration the velocity of river flows, the geological condition of each bridge and the extent of abutment erosion,” said Tsai Chun-yi (蔡俊育), a structural engineer and an assistant professor at National Central University.
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