Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering), Vol. 75, No. 2, I_73-I_78, 2019.

Storm Surge and High Waves due to 1997 Typhoon Linda: Uninvestigated Worst Storm Event in Southern

Le Tuan ANH1, Hiroshi TAKAGI2, Nguyen Danh THAO3

1School of Environment and Society, Tokyo Institute of Technology (2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan) E-mail: [email protected] 2Member of JSCE, Associate Professor, School of Environment and Society, Tokyo Institute of Technology (2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan) E-mail: [email protected] 3Associate Professor, Department of Port and Coastal Engineering, Ho Chi Minh City University of Technology (268 Ly Thuong Kiet St., Dist.10, Ho Chi Minh City, Vietnam) E-mail: [email protected]

Typhoon Linda in 1997 is considered to be the worst tropical ever to make landfall in the Mekong Delta, Southern Vietnam. Linda caused catastrophic social impact with over 3,000 fatalities and US$385 million in property loss. The fatalities were mostly fishermen and sailors who were caught at sea in Linda’s path and unable to escape. There is little information about Linda because of the lack of a detailed post-disaster investigation. In this study, we conducted an interview survey with local residents of Con Dao Island, where Linda passed nearby, to reveal how this historical disaster event remains in their memory. A numerical simulation using the coupled typhoon, , and wind-wave model was also performed to investigate the spatial extent of the storm surge and high waves during Linda’s passage. The results showed that the storm tide was not necessarily extreme, but reached 1.5 m in the delta. In comparison, waves off the Mekong Delta were estimated to be 8 m high, which appears sufficient to capsize many wooden fishing boats.

Key Words: Southern Vietnam, Con Dao Island, 1997 Typhoon Linda, storm surge, high wave, dis- aster awareness, fishing boat

1. INTRODUCTION Linda generated a storm surge of up to 0.7 m5), and wind-generated waves were nearly 3 m6) in the Compared to Northern and Central Vietnam, the northwestern part of the Gulf of Thailand. frequency of typhoons in Southern Vietnam—which However, few studies have examined the extent of includes the Mekong Delta (MD) and other remote the damage caused by Linda in Vietnam—despite islands—is relatively low. As such, the risk of a extensive devastation. Particularly, the physical typhoon disaster tends to be overlooked in this impact of the storm surge and high waves has yet to region; however, typhoons do occasionally make be scientifically investigated. The most severely landfall in the southern part of Vietnam1), 2). affected provinces, such as Ca Mau and Bac Lieu, are Typhoon Linda (meteorologically categorized as a remote areas that remained inaccessible by roads for severe tropical storm) of 1997 is considered to be the many weeks after the disaster7). worst and rarest ever to make While there has been a limited amount of landfall in Southern Vietnam. The sudden event of documentation by governmental institutes and local Linda caused catastrophic damage with over 3,000 authorities, it is difficult for ordinary researchers to deaths and US$385 million in property loss. The access. Additionally, Vietnam’s bureaucracy at the fatalities were mostly fishermen and sailors who time might have made it difficult for non- were caught at sea in Linda’s path and unable to governmental organizations and researchers to escape3), 4). investigate in the Mekong region. According to previous studies by Thai researchers, Less availability of information about Linda may

I_73 Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering), Vol. 75, No. 2, I_73-I_78, 2019. be also due to the limited mobility of international In this study, we also conducted a similar interview researchers at the time; specifically, the internet survey in Con Dao Island, which is located off the environment was insufficient to promptly conduct southeastern tip of Vietnam—approximately 230 km post-disaster surveys abroad8). south of Ho Chi Minh City (HCM). We administered In this study, we revisit Typhoon Linda in 1997 to a structured questionnaire to the local inhabitants of understand the characteristics and extent of the storm Con Dao in March 2017. Our primary intent was to surge and wind-generated waves using state-of-the- investigate the residents’ memory of Typhoon Linda, art numerical modeling. Particular attention in this as well as how Linda affected the general awareness research is given to identifying the risk of high waves of typhoon disasters. The questionnaire consisted of during Linda, which might have capsized many a number of different questions, including 5 main fishing boats far from the coast. questions:

I. Do you remember Typhoon Linda? 2. METHODOLOGY II. Did you evacuate during Linda? III. Do you fear typhoons? This section first describes the field surveys con- IV. Do you know how to evacuate from a typhoon ducted on Con Dao Island. Subsequently, a numerical storm surge? model that simulates typhoon, storm surge, and wind- V. How were your children educated about disasters generated waves are briefly explained. in school?

(1) Filed survey There are two main residential areas in Con Dao— one on the east coast and the other, a northern village We conducted a field survey in the MD in 2014 on the mountain (Fig. 1). As the result of the field and 2015 to investigate the perceptions of local survey conducted in the two areas, a total of 103 valid residents in terms of coastal disasters. These studies responses were collected. It should be noted that revealed a relatively high awareness among locals tourists and residents who recently relocated to Con 2), 9) regarding typhoons and storm surge in the delta . Dao were intentionally excluded from the survey.

Fig. 1 Circular plots on this satellite image indicate the towns of Con Dao Island where we conducted the survey. (White dots: East coast; yellow dots: Northern village.) A total of 103 questionnaires were collected in Con Dao. The insets show interviews with local witnesses.

(2) Typhoon, Storm Surge, and Wind-Generated Wave developed to simulate the storm surge during the pas- Simulation sage of Linda. The reliability of our model was veri- fied for several strong typhoons, such as Haiyan of We used the fluid dynamics module Delft3D- 201310), Goni of 201511), and Hato of 201712). The ty- FLOW, coupled with a parametric typhoon model we phoon model calculated both the pressure and wind

I_74 Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering), Vol. 75, No. 2, I_73-I_78, 2019. fields using parameters obtained from the Japan Me- the Gulf of Thailand. Among many physical pro- teorological Agency (JMA) tropical cyclone (TC) cesses, depth-induced wave breaking, bottom fric- best-track dataset (http://www.jma.go.jp/jma/jma- tion, wind-wave growth, white-capping, and quadru- eng/jma-center/rsmc-hp-pub-eg/trackarchives.html). plet interactions were activated in SWAN simula- That is, the central positions and pressures at every tions. The simulation was run from 06:00 on Novem- recording period were used as parameters. The max- ber 1st to 00:00 on November 4th, 1997 (UTC). imum wind radius, which was not contained in the best-track data, was estimated from the central pres- 11) sure . 3. RESULTS Although Delft3D can be applied to three-dimen- sional phenomena, the present study used a two-di- (1) Memory of Linda and Awareness of Typhoon Dis- mensional horizontal grid. Thus, the code becomes a asters in Con Dao Island shallow-water wave model, which is commonly used to simulate long waves—such as storm surges, tsuna- mis, and tidal propagation. The computational do- main encompassed a wide area that included the MD between 6°N–99°E and 17.5°S–113°E (the cyan grid in Fig. 2). Oceanic bathymetry within the computa- tional domain was obtained from the General Bathy- metric Chart of the Oceans (GEBCO). In addition, we used the SWAN model coupled with Delft3D-FLOW to estimate the wave caused by Linda. The result of the simulation was verified with wave data obtained from a number of available wave Fig. 3 Questionnaires results regarding people awareness and stations located in the Gulf of Thailand5) to confirm preparedness in Con Dao. the accuracy of the model. Due to the lack of wave data during Linda, the numerical model is useful for Because Linda occurred in 1997, we interviewed estimating the maximum wave height and mapping only those who might remember the event. As a re- its spatial distribution over the East Sea of Vietnam. sult, most of the questionnaires (92.2%) were col- lected from people over 30 years of age. Neverthe- less, a small number of the younger population were also interviewed to investigate their general percep- tion of typhoon disasters. Fig. 3 shows the results from the questionnaires. It is remarkable that 83.5% of respondents in Con Dao remembered Typhoon Linda. The 16.5% that did not recall Typhoon Linda includes the young re- spondents who were born after the event and those who had recently migrated from the mainland and did Fig. 2 Simulation grids, combining larger and smaller domains. not live on the island during Linda. Of the respond- The blue domain focuses on Southern Vietnam, the red, ents, 84.5% confirmed that they are afraid of ty- the Gulf of Thailand. (Yellow dots: wave observation phoons in general. According to one local resident, it stations; red line: Linda’s path) was likely that fear for typhoons did not exist among the local population before Linda. Regarding prepar- SWAN is a third-generation wave model that com- edness after the event, 88.3% of respondents con- putes irregular, short-crested, wind-generated waves firmed that they know how to evacuate in the event in coastal regions and inland waters13). The SWAN of a typhoon and storm surge. model was coded based on the wave-action balance Despite the strong winds caused by Linda, more equation with sources and sinks, and provides nesting than half of respondents (55.8%) did not evacuate. application to a parent grid. There were two reasons for this: First, people did not We generated two computational domains. The know where to evacuate because this was the first larger domain was used as the parent grid with a res- time they had experienced a storm. Second, concrete olution of 0.05ox0.05o (Fig. 2). Two smaller finer buildings in the east coast area—where a large popu- grids were used as the nested internal grid with a res- lation lived—were used to accommodate soldiers olution of 0.02ox0.02o to cover the area off the coast during the Vietnam War. On this basis, those resi- of Southern Vietnam—including Con Dao Island and dents believed that their house was the safest place,

I_75 Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering), Vol. 75, No. 2, I_73-I_78, 2019. and thus, stayed home. However, it appears that local residents underesti- mated and were not well-prepared for Linda. In fact, strong winds caused many wooden houses to col- lapse. Although there were no reported casualties in the inland communities, many fishing boats were wrecked by strong winds and high waves when an- chored at the pier.

(2) Storm Surge Induced by Linda Fig. 6 Comparison between observed and simulated maximum Fig. 4 shows the central pressure and maximum water levels, including storm surge and tide, during Linda wind speed obtained from the JMA. The background from three locations in the MD. Observed data were de- map in Fig. 5 shows the distribution of the maximum rived from our previous study9). surge heights generated by the typhoon–hydrody- namic coupling model. The results suggest that the (3) Waves Generated by Linda abnormal water level reached the range of 1-2 m in the MD. The estimated maximum water levels at We simulated the possible significant wave height, three stations (indicated by red dots in Fig. 5)—in- Hs, generated during the passage of Linda. The ab- cluding My Thanh, Ganh Hao, and Ca Mau—fit well sence of wave stations along the path of Linda with the observed data (for Ca Mau the observed val- through the East Sea of Vietnam in 1997 led to a dif- ues were based on the interviewees’ memory) (Fig. ficulty in validating the wave height in the oceanic 6)9). Meanwhile, the numerical simulation also shows basin off the MD. that the seawater level (including the tide) at Con Dao was approximately 0.3 m while Linda passed. The questionnaire results revealed that 85 out of 86 peo- ple who still remembered the damage caused by Linda replied that there was no flood. Because the majority of the area is occupied by hills and moun- tains, such a minor rise in water level could not cause any inundation.

Fig. 7 Simulated and observed wave heights at Huahin, Ko Chang, and Rayong as Linda approached the Gulf of Thailand (Observed data retrieved from the previous study 5)).

Fig. 4 Central pressure and wind speed during Linda (Vietnam- ese local time).

Fig. 8 Wave-height distribution when Linda crossed the south side of Con Dao at 7:00 a.m. on November 2nd, 1997 (Vi- etnamese local time).

Fig. 5 Distribution of the storm surge induced by Typhoon Alternatively, we used wave data observed at three Linda, estimated by a typhoon-storm surge integrated stations—Huahin, Rayong, and Ko Chang (Fig. 2)— model. in the Gulf of Thailand (toward which Linda

I_76 Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering), Vol. 75, No. 2, I_73-I_78, 2019. proceeded after passing the MD) for the validation of unable to enter were forced to stay outside the port, the wave model5). Fig. 7 illustrates the good agree- and some were sunk due to high waves and strong ment between the maximum simulated Hs and the winds. values observed at the stations. The difference be- Awareness about disasters has to do with many tween Hs values at Huahin was 0.69 m, while those factors. Without proper efforts to maintain aware- of the other two stations were inappreciable. Fig. 8 ness, it will gradually fade over time18). Con Dao was shows the wave distribution around Con Dao during once an unpopulated island used only for political Linda’s passage. The wave height off the island was prisoners. After the Vietnam War, people moved estimated to be over 8 m. from the mainland, leading to the present population of approximately 7,000. New immigrants—who did not experience Typhoon Linda—gradually became 4. DISCUSSION the majority on the island, thus inhibiting the dissem- ination of the experience from older to younger gen- Fig. 9 shows the major fishing spots off the MD, erations. obtained from the Environmental Impact Assessment We found a tsunami evacuation instruction panel for the project “Sao Vang–Dai Nguyet Oil Field”14). (Fig. 10) near the pier that exemplifies efforts by the There are 2 distinct fishing seasons in Vietnam—lo- local government in Con Dao to raise awareness of cally referred to as the north season (from October to coastal disasters among local inhabitants and tourists. March) and south season (from April to September). However, according to the questionnaires, (Fig. 3) Linda’s path coincided with fishing spots in the north only a small percentage (7.8%) of children learn season. The rectangular and circular areas in Fig. 9 about storm surge in school. To address this, disaster represent the north season shrimp- and squid-catch- evacuation drills could be held by inviting all resi- ing spots, respectively. dents—including children and the elderly. In partic- According to interviews with locals, many fisher- ular, for future disaster management in the region, men were still at sea when Linda was approaching the disaster education for children should be imple- East Sea. Fishermen did not seriously consider that mented as a tangible and continuing effort. they had encountered a strong storm because such rarely occurs in this region. The Vietnam Television Online Newspaper15) also reported that fishermen un- derestimated the warning and continued to push off—even when the government announced that Linda had strengthened and would soon approach the MD. As a result, many boats might have been caught by Linda at sea, despite trying to escape from the ty- phoon’s path. As shown in Fig. 9, there were two possible shortcuts for fishermen to flee from these fishing spots to shelter (the white arrows). For the western- most spot, fishermen escaped from Hon Khoai (on Fig. 9 Major fishing spots in Southern Vietnam (the white arrows the southern end of the MD) to Hon Chuoi Island (on in the right inset show the possible route toward Con Dao that many fishing boats took to escape from high waves the west side of the MD) because it was thought that during Linda; those in the left inset show the escape route this island seemed to be safe and out of the forecasted according to interviews with fisherman in the local news- typhoon path, according to witness interviews in the paper16)). 16) local newspaper . Some interviewees said that Con Dao was located directly on the path of Linda, result- ing in the unfortunate loss of many human lives. It was estimated that Linda proceeded at a speed of approximately 25 km/h when it passed near the fish- ing spots. The majority of fishing boats in Vietnam were made of wood. It is not difficult to imagine that many wooden boats might have been caught by high waves during Linda because they were too slow (ap- proximately 11-15 km/h under normal sea condi- tions) to escape17). A number of boats were able to safely arrive in Con Dao. However, Con Dao had a limited amount of space for boats. Those that were Fig. 10 Tsunami instruction panel in Con Dao

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5. CONCLUSION 6) Wannawong W., Humphries U W., Wongwises P., Vongvisessomjai S., Lueangaram W. A two-dimensional wave prediction model along the best track of Typhoon It appears that coastal hazards in the Mekong Linda 1997, American Journal of Environmental Sciences 6 Delta—particularly storm surges and typhoons— (3): 280-285, 2010. have not received as much attention by academics 7) The Nation. Thai daily newspaper, November 15, 1997. and disaster risk managers as they probably deserve. 8) Esteban M., Takagi H., Shibayama T. Handbook of Coastal Typhoon Linda remains the most catastrophic Disaster Mitigation for Engineers and Planners, Elsevier, Page 780, 2015. typhoon to have hit Southern Vietnam. The results of 9) Takagi H., Anh L. T., Thao N. D. 1997 Typhoon Linda our questionnaire show that the majority of local Storm Surge and People's Awareness 20 Years Later: residents—especially fishermen—underestimated Uninvestigated Worst Storm Event in the Mekong Delta, the potential risk of typhoons (including Linda) at Nat. Hazards Earth Syst. Sci. Discuss., European that time due to their low frequency. Many fishermen Geosciences Union, 2017. were caught by Linda at sea while trying to escape 10) Takagi H., Esteban M., Shibayama T., Mikami T., from the typhoon path. Simulation results revealed Matsumaru R., Leon M. D., Thao N. D., Oyama T. & Nakamura R. Track analysis, simulation, and field survey of that the storm surge was not very high. However, the 2013 storm surge, J. Flood Risk wind-generated waves off Con Dao Island—which Management, 10(1), 42-52., 2017. served as a shelter for fishermen—were estimated 8 11) Takagi H., Wu W. Maximum wind radius estimated by the m high during Linda’s passage. According to 50 kt radius: improvement of storm surge forecasting over interviews, the local population clearly remembered the western North Pacific, Nat. Hazards Earth Syst. Sci., the event and had a relatively high degree of European Geosciences Union, 16, pp. 705-717, 2016. awareness about the dangers posed by typhoons after 12) Takagi H., Xiong Y., Furukawa F. Track analysis and storm Linda. However, residents are not well prepared to surge investigation of 2017 Typhoon Hato: were the warning signals issued in and timed face these natural disasters because the frequency of appropriately?, Georisk, pp.297-307., 2018. typhoon is significantly low, and thus awareness- 13) Booij, N., Ris, R.C., Holthuijsen, L.H. Third-generation building and education for local residents should be wave model for coastal regions 1. Model description and prioritized in disaster management for the region. validation, J. Geophys. Res. 104 (4), 7649–7666, 1999. 14) Environmental Impact Assessment of project Development Sao Vang – Dai Nguyet Oil Field (in Vietnamese), ACKNOWLEDGMENT: This research was funded https://www.jbic.go.jp/ja/business- by the Japan Society for the Promotion of Science areas/environment/prjects/pdf/54407_11.pdf. (JSPS) KAKENHI (Grant Number 16KK0121). 15) The Documentary from Vietnam Television Online Newspaper (Vtv.Vn) about typhoon Linda. https://vtv.vn/trong-nuoc/nhin-lai-sieu-bao-linda-sau-20- REFERENCES nam-20171028183143701.htm 1) Takagi H., Thao N. D., Esteban M., Mikami T., Cong L. V., https://vtv.vn/trong-nuoc/noi-am-anh-mang-ten-linda- Ca L. T. Coastal Disasters in Vietnam, IN: Esteban M., 20171101134209107.htm Takagi H., Shibayama T. (eds) Handbook of Coastal 16) Local newspaper about typhoon Linda. Disaster Mitigation for Engineers and Planners, Elsevier, https://news.zing.vn/ky-uc-kinh-hoang-sau-20-nam-tham- 235-255, 2015. hoa-bao-linda-post792144.html 2) Anh L. T., Takagi H., Thao N. D., Esteban M. Investigation 17) Research Institute For Marine Fisheries, Effect of typhoon of Awareness of Typhoon and Storm Surge in the Mekong and tropical depression on fishing boat. (in Vietnamese) Delta – Recollection of 1997 Typhoon Linda, Journal of (Ảnh hưởng của bão và áp thấp nhiệt đới đến tàu thuyền khai Japan Society of Civil Engineers, Ser. B3 (Ocean thác hải sản. 11-2009). Engineering), 73(2), pp. 168-173, 2017. 18) Esteban, M., Tsimopoulou, V., Mikami, T., Yun, N. Y., 3) The Nation. Thai daily newspaper, November 6, 1997. Suppasri, A. and Shibayama, T. (2013) “Recent Tsunami 4) UNDP. Summing-up report on disaster situations in recent Events and Preparedness: Development of Tsunami years and preparedness and mitigation measures in Vietnam, Awareness in Indonesia, Chile and Japan”, Journal of 2003.The Nation. Thai daily newspaper, November 15, Disaster Risk Reduction, pp. 84-97. 1997. 5) Aschariyaphotha, N., Wongwises, P., Humphries, U.W. & Wongwises, S. Study of storm surge due to Typhoon Linda (Received February 7, 2019) (1997) in the Gulf of Thailand using a three-dimensional (Accepted April 24, 2019) ocean model. Applied Mathematics and Computation 217: 8640-8654., 2011.

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