COMPARISONS OF WAVE OVERTOPPING DISCHARGES AND DAMAGES OF THE NTOU VERTICAL SEAWALL DUE TO TWO SIMILAR SUPER TYPHOONS ON KEELUNG COAST OF TAIWAN

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1 COMPAISONS OF WAVE OVETOPPING DISCAGES AND DAMAGES OF TE NTOU VETICAL SEAWALL DUE TO TWO SIMILA SUPE TYPOONS ON KEELUNG COAST OF TAIWAN Da-Wei Chen 1 Shiaw-Yih Tzang Shan-wei Ou In thi tudy, SWAN model wa firt applied to obtain wave condition during Typhoon erb (1996) and Kroa (7). Then the reult were ued for etimating the wave overtopping dicharge with exiting empirical formulae elected from EurOtop manual. In the EurOtop formulae, calculation of overtopping dicharge can be improved by adapting average wave period (T m-1,) for well condition. The reult how that the peak overtopping dicharge during Typhoon erb (1996) are larger than thoe during Typhoon Kroa (7) at the two elected ite. In addition, the water depth at toe of eatern NTOU eawall (NTOU ) are hallower than that at northern NTOU eawall (NTOU 1) o that the dicharge at NTOU 1 are larger than thoe at NTOU. The calculation how that the peak wave overtopping dicharge during both typhoon are greater than the criteria for damage on back lope of eawall, which agree with the NTOU eawall failure event during Typhoon erb. The predicted failure doe not again happen to NTOU eawall during Typhoon Kroa implying the effective reduction in overtopping dicharge by lifting up 1m of the cret after rebuilding the previouly damaged eawall. Keyword: wave overtopping; vertical eawall; tructure damage; typhoon INTODUCTION Taiwan i located on the edge of wetern Pacific Ocean o that it coatal area are uually threatened by violent wave during typhoon period. In recent year, the eawall of National Taiwan Ocean Univerity (NTOU) in Keelung of northeatern Taiwan have freuently uffered conecutive damage due to typhoon wave. In 1996, a uper Typhoon erb truck the vertical NTOU eawall of the reclaimed campu cauing partial damage on the parapet, a hown in Fig. 1 (a). According to Tai et al. (6), the damage were primarily caued by ignificant wave overtopping due to extreme high water level coniting of high pring tide and torm urge and aociated large wave. Tzang et al. (9) have further calculated the overtopping dicharge with exiting empirical formulae and hown that during certain period the dicharge could be greater than the deign criteria according to Coatal Engineering Manual (CEM, ). Later, the NTOU eawall had been conecutively damaged by typhoon in the ame and the following year, i.e. Typhoon Zane(1996), Typhoon Winnie(1997) (Tzang and iao, 1999). The eawall were then rebuilt in 199 by mainly lifting up 1m of the cret height. owever, in 7, another uper Typhoon Kroa with imilar path of Typhoon erb (ee Fig. ) truck the rebuilt eawall but caued only damage on the concrete covering of the drainage ditche right behind the parapet. From a imilar previou cae, Tzang et al. () reported that typhoon wave might reult in intene water hammer drainage in the channel by breaking on the drainage outlet on vertical face of the eawall. The trong upward jet could ubeuently break the covering and puh away broken piece. Then the following overtopping water could have pounded on and diplace thoe broken concrete piece further, a hown in Fig. 1 (b). In order to undertand the different effect of wave overtopping dicharge over the lifted-up cret elevation of the rebuilt eawall during Typhoon Kroa, it i aimed in thi tudy at carrying out calculation and comparion with exiting empirical formulae and thoe of EurOtop Manual. 1 Department of arbor and iver Engineering, National Taiwan Ocean Univerity, Pei-Ning oad, Keelung, Taiwan,,.O.C. Department of arbor and iver Engineering, National Taiwan Ocean Univerity, Pei-Ning oad, Keelung, Taiwan,,.O.C. Department of Environmental eource Management, Tajen Univerity, Weiin oad, Sin-er Village, Yanpu Townhip, Pingtung, Taiwan, 97,.O.C. 1

2 COASTAL ENGINEEING 1 (a) Typhoon erb (1996) (b) Typhoon Kroa (7) Figure 1. The damage on NTOU eawall. OVETOPPING FOMULAE In recent year, many finding have been obtained from invetigation on overtopping flow over coatal tructure in everal large program project of European Union. A ummarized in Coatal Engineering Manual, mean overtopping dicharge are more widely adopted, though the local overtopping dicharge (in m //m) from a ingle wave can ometime be 1 time larger during the torm peak (CEM, ). Empirical Formulae The mean overtopping dicharge are defined a the average over 5 or 1 random wave from the model tet (Bruce et al., 1). For uite a longtime, Goda formulae (Goda, 195) have been the commonly adopted method, and calculation can be directly obtained from deign diagram for cae of vertical wall and block mound eawall. But a diadvantage of thi method i that interpolation of the diagram by the uer i reuired. To overcome the diadvantage, ome reearcher had further extended the work of Goda to take into account of bottom lope, wave teepne and loping breakwater, e.g. erbert (199); Jenen and Sorenen (1979). Franco et al (199) tudied wave overtopping over variou caion breakwater, epecially in deep water by unbroken wave. Their model i repreented by dimenionle parameter Q * for dicharge and * for freeboard from pecific tructure geometry. Baed on additional model tet, Allop et al. (1995) found that formulae of Fanco et al. (199) would underetimate for larger

3 Latitude (deg.) COASTAL ENGINEEING 1 value of c /, where c i the freeboard height and the ignificant wave height. They propoed that thi parameter can be ued in deep and hallow water. Later, Beley et al. (199) extended formulae by Allop et al. (1995) with another parameter d * to deal with influence of a berm in front of a vertical wall. Franco et al. (1999) had alo revied their previou verion by taking in new parameter from the reanalyi of the data ued by Franco et al. (199), and with additional reult from D model tet. 6 1/7 1: 1/7 : /1 : 7/1 : /1 : 1/6 : 1/6 16: 1/6 1: 7/1 1: 7/1 : 1/6 : 1996 Typhoon erb 7 Typhoon Kroa Longitude (deg.) Figure. The path of typhoon erb(1996) & Kroa(7). EurOtop According to EurOtop (7), the manual i developed from three manual: the Environment Agency Manual on Overtopping (U.K.), the TAW Technical eport on Wave run-up and wave overtopping at dike (Netherland), and the German Die Küte EAK (). The new combined manual ha extended and developed the part of thoe manual to dicu wave run-up and overtopping for coatal tructure of variou type, including eawall, flood embankment, breakwater, and horeline tructure. In EurOtop (7), the predicting formulae are typically applicable for three type of eawall: plain vertical eawall, vertical compoite wall, and vertical battered wall. For afety aement, the predicted dicharge are baed on either determinitic deign or probabilitic deign. The probabilitic deign take into account the effect of uncertaintie from all parameter including wind, wave and urge tatitic. It i noted that the pectral period (T m-1, = m -1 /m ) i adopted a the parameter of wave period. In general, the relationhip between the pectral period (T m-1, ) and the commonly adopted peak period (T p ) are T p = 1.1 T m-1,. Since plain vertical eawall formulae of EurOtop (7) are better formulated, the overtopping dicharge are imulated by plain vertical formulae in thi paper. WAVE SIMULATION To imulate the typhoon wave, the work preented herein adopt primarily the SWAN model of verion.7. The far-field computational domain of the neted grid, a hown in Fig. (a), cover the range from 1to N and 11to 1E. The area i elected to include the affecting procee of a typhoon. The near-field computation domain cover the area in northeatern Taiwan including Keelung, which are alo detailed in Fig. (b). It i een in Table that for far-field wave imulation the grid pacing i km and the computational time tep i 15

4 COASTAL ENGINEEING 1 min. In the near-field neted domain grid ize of 5 km, m and m are for layer, and, repectively. In thi tudy, the SWAN model ha been driven by 1m wind field above ea water level obtained from the Cro-Calibrated Multi-Platform (CCMP). They are the obervational data per 6 hr with grid accuracy of.5 by NASA. In addition, in order to improve high-reolution in 1 hr for computational domain when typhoon approach to Taiwan, the wind field model of CCMP wa coupled with VM (ankin-vortex Model) by interpolation on each computational grid. Table 1. Empirical formulae and thoe hydraulic condition. Formulae Allop et al. (1995) Type / wave Vertical (unbroken) Vertical (broken) ydraulic condition. < c / <., ignore water depth. (including unbroken & broken wave ) h *., for impacting wave h * >., for reflecting wave model Q g 1 Q * gh h Dimenionle Freeboard Dimenionle dicharge Q c Q aexp b c * h Q a b Allop et al. (1995) & Beley et al. (199) Compoite (unbroken) d * >. or c / <1.5, for unbroken wave Compoite (broken) Compoite (broken) d *. or c / >1.5, for broken wave d<, tructure with emergent mound. Q Q g 1 * g d 1 Q * gh d c Q aexp b c * d Q aexp b c d d * Q a b g g m, deep m, deep h h h h g g m m * Table. EurOtop formulae and thoe hydraulic condition. Formulae Type / wave ydraulic condition c.exp.6 Probabilitic m (unbroken) h*., c.1 c/ m.5.exp 1. Determinitic m (unbroken).6.6 g gh gh * gh * gh * m c 1.51 h* m c.1 h* m c.71 h* m c.1 h* m mm. c.exp.16m m1, 1, m, deep mm. c.exp 1.95m m1, 1, m, deep Zero Freeboard h*., c/ m (unbroken) Probabilitic h*., (broken, non-impulive) c Determinitic. h* 1. (broken, non-impulive) m Probabilitic (broken, impulive, ubmerged toe) Determinitic (broken, impulive, ubmerged toe) Probabilitic (broken, impulive, emergent toe) Determinitic (broken, impulive, emergent toe) h*., c h. * m h*., m 1,.5. c. mm 1, 5. m, deep.55 c 1.6 m, deep Table. Information of computational domain. neted Geographic Data ource Filename eolution grid reolution Layer 1 National Oceanographic Data Center ETOPO1 x=y=. ~ km Layer National Center of Ocean eearch TaiDBMV6 x=y=. ~ 5 km Layer Electronic Chart Sytem x=y=. ~ m Layer Meaurement x=y=.5 ~ m

5 Latitude (deg.) Latitude (deg.) COASTAL ENGINEEING 1 5 Layer Longitude (deg.) (a) Far-field computational domain Layer Layer Suao ualien Longitude (deg.) (b) near-field computation domain Figure. Coatal topography of the neted domain. Model Validation Comparion of the predicted wave height and period with field data meaured at ualien and Suao tation on the eat coatal water of Taiwan during Typhoon erb (1996) and Kroa (7) are hown in Fig. (a) and (b). The circle repreent the meaured data and the curve repreent the predicted reult. It can be een from Fig. (a), the meaured maximum ignificant wave height ( ) of 7.6 m (T m = 1. ) occurred at 6: on July 1 during Typhoon erb, while the imulated ignificant wave height of. m (T m = 1. ) occurred at 17: on July 1. In addition, in Fig. (b), the meaured maximum of 11.7 m (T m = 1.6 ) occurred at 1: on Oct. 6 during Typhoon Kroa, while the imulated maximum of.5 m (T m = 1. ) occurred at 1: on Oct. 6. ence, the comparion how that the imulated value of Typhoon Kroa agreed better with meaured data on magnitude and occurrence time than the imulation of Typhoon

6 mean wave period (ec) ignificant wave height (m) mean wave period (ec) ignificant wave height (m) 6 COASTAL ENGINEEING 1 erb did. But agreement between the imulation and meaured data through the whole time erie for both typhoon are imilar. 1 Meaurement SWAN ualien : : 11: : 11: : 11: : 1996/7/9 1996/7/ 1996/7/1 1996//1 date/time (a) Typhoon erb 1 Meaurement SWAN Suao : : 11: : 11: : 11: : 7/1/ 7/1/5 7/1/6 7/1/7 date/time (b) Typhoon Kroa (7) Figure. Comparion of ignificant wave height and period predicted by the SWAN wave model with meaurement during the paage of Typhoon erb & Kroa.

7 COASTAL ENGINEEING 1 7 Wave condition The NTOU eawall have uffered damage due to typhoon-induced wave for many time in the pat, epecially in eatern wall (NTOU ) and northern wall (NTOU 1), a hown in Fig. 5. The tatic water depth at the two location are m (NTOU 1) and m (NTOU ), repectively. The imulation by SWAN model how that at the two ite of NTOU 1 and NTOU, maximum are.5 m (1. ) and. m (1. ) at : on July 1 during Typhoon erb. The firt peak are.6 m (1.6 ) and.6 m (1. ) at 16: on Oct. 6 while the econd peak are. m (9.1 ) and. m (9. ) at : on Oct. 6 during Typhoon Kroa, a hown in Fig. 7 and. owever, comparion of the occurring time of maximum along typhoon path, the imulation of two location during Typhoon Kroa how that the firt peak value of were primarily due to nearly tationary typhoon move offhore the eatern Taiwan (ee Fig. ).The econd peak value of were induced by typhoon low preure center a it continued to pa over Keelung. Typhoon Winnie (1997) Sinlaku () NTOU_1 Typhoon Zane (1996) Typhoon erb (1996) Typhoon erb (1996) Sinlaku () NTOU_ Typhoon erb (1996) Typhoon Kroa (7) ( 柯羅莎 ) N Typhoon Sinlaku () Figure 5. The ite of conecutive damage and predicted wave condition by SWAN model. WAVE OVETOPPING DISCAGES Parameter etting The NTOU eawall tood on rocky bottom with an offhore lope of about 1:1. The eawall wa originally deigned a a vertical compoite tructure with a berm of -ton tetrapod. But the foundation uarry tone were only placed at ite with elevation under E.L. -. m. The elevation of crown wall were E.L. +6 m for original wall during Typhoon erb and E.L. +7 m for rebuilt wall during Typhoon Kroa, a hown in Fig. 6 (a) and 6 (b). In particular before the attack of Typhoon erb in 1996, the eawall had uffered from everal typhoon attack o that many of the berm tetrapod might have been dilocated to be more like a vertical wall tructure. Thu, the overtopping flow dicharge hall be calculated by elected empirical formulae for both cae. For the imulation, the water depth including typhoon urge were elected from the nearby tidal tation in Port of Keelung. To predict mean overtopping flow rate, mot of the empirical formulae reuire wave condition at toe and configuration parameter of coatal tructure. For Goda formulae, the euivalent deep-water wave height and deep-water wave length are reuired to obtain overtopping dicharge within certain water depth. In particular, ome of the calculation need to

8 COASTAL ENGINEEING 1 be derived by interpolation from the diagram. The hydraulic coefficient and aociated parameter of the applied formulae are repectively lited in Table 1 and Table. Analyi Deign of cret level for coatal tructure generally take into account allowable overtopping dicharge. For embankment eawall, the critical value of mean overtopping dicharge are marked together with the predicted value. It can be een in Fig. 7 and Fig. that the prediction had one peak value during Typhoon erb and two peak value during Typhoon Kroa. In addition, the overtopping dicharge predicted by determinitic and probabilitic method from EurOtop manual are alo diplayed in thee two figure. Moreover, all the prediction by EurOtop manual have adopted average wave period (T m-1, ) for well condition. Comparion of the ea water level at two ite in two typhoon have hown that the peak value of. m during Typhoon erb i larger than the peak value of 1.71 m during Typhoon Kroa. During Typhoon erb, the peak water level occurred at : on July 1 while peak ignificant wave height occurred about 1 hour later a the typhoon approached, a hown in Fig. 7(a). On the contrary, the occurrence time during Typhoon Kroa for maximum value of important parameter are different from each other, a hown in Fig. (a)..5 m (a) Old wall E.L. +7. E.L. +5. EL. +. EL depth M.W.L L.L.W.L (b) New wall Figure 6. NTOU eawall originally deigned for new and old.

9 mean overtopping dicharge (m /ec/m) ignificant wave heoght (m) mean overtopping dicharge (m /ec/m) ignificant wave heoght (m) period (ec) ea water level (m) period (ec) ea water level (m) COASTAL ENGINEEING 1 9 Ditance from typhoon center to Keelung ignificant wave height (m) 1996 Typhoon erb mean period (ec) NTOU_ average wave period (m -1 /m ) EMBANKMENT SEAWALLS Damage even if fully protected Damage even if back lope not protected Allop et al.(1995)-vertical Allop et al.(1995)-compoite Beley et al.(199)-compoite EurOtop()-Determinitic EurOtop()-Probabilitic 1996/7/9 : Damage even if cret not protected.1 No damage 1 11: : 11: : 11: : 11: : 1996/7/9 1996/7/ 1996/7/1 date/time 1996//1 (a) NTOU 1 Ditance from typhoon center to Keelung Typhoon erb NTOU_ 16 ignificant wave height (m) mean period (ec) average wave period (m -1 /m ) EMBANKMENT SEAWALLS Damage even if fully protected Damage even if back lope not protected Allop et al.(1995)-vertical Allop et al.(1995)-compoite Beley et al.(199)-compoite EurOtop()-Determinitic EurOtop()-Probabilitic 1996/7/9 : Damage even if cret not protected.1 No damage 11: : 11: : 11: : 11: : 1996/7/9 1996/7/ 1996/7/1 date/time 1996//1 (b) NTOU Figure 7. The calculated overtopping dicharge at two ite during Typhoon erb (1996).

10 mean overtopping dicharge (m /ec/m) ignificant wave heoght (m) mean overtopping dicharge (m /ec/m) ignificant wave heoght (m) period (ec) ea water level (m) period (ec) ea water level (m) 1 COASTAL ENGINEEING Ditance from typhoon center to Keelung Typhoon Kroa NTOU_1 16 ignificant wave height (m) mean period (ec) average wave period (m -1 /m ) EMBANKMENT SEAWALLS Damage even if fully protected Damage even if back lope not protected Allop et al.(1995)-vertical Allop et al.(1995)-compoite Beley et al.(199)-compoite EurOtop()-Determinitic EurOtop()-Probabilitic 7/1/6 : Damage even if cret not protected.1 No damage 1 11: : 11: : 11: : 11: : 7/1/ 7/1/5 7/1/6 date/time 7/1/7 (a) NTOU Ditance from typhoon center to Keelung Typhoon Kroa NTOU_ 16 ignificant wave height (m) mean period (ec) average wave period (m -1 /m ) EMBANKMENT SEAWALLS Damage even if fully protected Damage even if back lope not protected Allop et al.(1995)-vertical Allop et al.(1995)-compoite Beley et al.(199)-compoite EurOtop()-Determinitic EurOtop()-Probabilitic 7/1/6 : Damage even if cret not protected.1 No damage 11: : 11: : 11: : 11: : 7/1/ 7/1/5 7/1/6 date/time 7/1/7 (b) NTOU Figure. The calculated overtopping dicharge at two ite during Typhoon Kroa (7).

11 COASTAL ENGINEEING 1 11 The peak value of predicted overtopping dicharge at two ite are. (NTOU 1) and.71 m //m (NTOU ) during Typhoon erb, and they have occurred at almot the ame time a typhoon center cloed. But the peak prediction during Typhoon Kroa are.9 (NTOU 1) and.6 m //m (NTOU ) when the typhoon tationed offhore eatern Taiwan. Later, the econd peak value are.11 (NTOU 1) and.1 m //m (NTOU ) when the typhoon continued and approached Keelung. The reult how that the water depth of NTOU are hallower than that of NTOU 1 while the dicharge at NTOU 1 are larger than thoe at NTOU. The reult in different ite how that the calculation with Allop (1995) and Beley (199) at NTOU 1 are larger than thoe at NTOU, the calculation with probabilitic method are lowet during Typhoon Kroa. Moreover, the reult in different formulae how that the calculation by Allop vertical formula are larger than other in addition to the reult with determinitic method. The calculation with Allop compoite formula at NTOU 1 are larger than thoe with Beley, but the calculation at NTOU with Beley are larger than thoe with Allop. According to Tai et al. (6), the old eawall had uffered rupture of parapet and loing of backfill oil and the reulting flooding on campu due to Typhoon erb. Thu by comparing with the lowet criteria for damage on unprotected lope, i.e.. m //m, it i confirmed that all maximum prediction during Typhoon erb have exceeded the criterion for both tructure type at both ite. On the other hand, mot of the prediction during Typhoon Kroa are een to be lower than the criterion In fact, only the old eawall ha uffered upertructure damage but they were not een to happen again on the rebuilt eawall during Typhoon Kroa. Thi imply implie that the rebuilt eawall could effectively defend wave impact on the parapet of eawall. Table. The overtopping dicharge at rebuilt eawall by reducing 1m during Typhoon Kroa. B (E.L. +7m) A (E.L +6m) (A-B)/A Allop et al. vertical Allop et al. compoite Beley et al. compoite EurOtop Determinitic EurOtop Probabilitic Allop et al. vertical 17 Allop et al. compoite 1 Beley et al. compoite 19 EurOtop Determinitic 16 EurOtop Probabilitic 16 It i particularly illutrated In Table that a the cret level of the rebuilt eawall decreae by 1m, mot of the calculated average dicharge have increaed 9~7%. ence, the rebuilt eawall ha played an effective role on reducing the overtopping dicharge by lifting up the cret by only 1m during Typhoon Kroa. By comparing the maximum dicharge with the determinitic method of EurOtop manual during Typhoon Kroa with the ame cret level of E.L. +6 m, the peak overtopping dicharge increae to be.5 (NTOU 1) and.5 (NTOU ) m //m, repectively. The maximum dicharge at NTOU during Typhoon Kroa i even larger than that during Typhoon erb. Thi further confirm the effect of higher cret elevation on reducing wave overtopping. CONCLUDING EMAKS In thi tudy, the overtopping dicharge at NTOU eawall by the two typhoon with imilar path, trength, and wave condition but cauing different eawall damage are etimated with exiting empirical formulae including thoe of EurOtop manual. On aplying the EurOtop formulae, calculation of overtopping dicharge adopt the average wave period (T m-1, ). The reult how that the peak overtopping dicharge during Typhoon erb (1996) are larger than thoe during Typhoon Kroa (7) at the two elected ite. In addition, the water depth at toe of eatern NTOU eawall (NTOU ) are hallower than that at northern NTOU eawall (NTOU 1) reulting in larger dicharge at NTOU 1 than thoe at NTOU. The calculation how that the peak wave

12 1 COASTAL ENGINEEING 1 overtopping dicharge during Typhoon erb are all greater than the criteria for damage on back lope of eawall. Thi agree well with the NTOU eawall failure event during Typhoon erb. The predicted failure doe not again happen to NTOU eawall during Typhoon Kroa implying the effective reduction in overtopping dicharge by lifting up 1m of the cret through rebuilding the previouly damaged eawall. So far, the complex phyical mechanim due to interaction of fluid-tructure i yet to be explored with further tudie. EFEENCES Allop, N.W.., Beley, P. and Madurini, L., Overtopping performance of vertical and compoite breakwater, eawall and low reflection alternative, Final Proceeding MCS Project Workhop, Alderney, United Kingdom. Beley, P., Stewart, T. and Allop, N.W.., 199. Overtopping of vertical tructure: new prediction method to account for hallow water condition, Proc. Conf. Coatline, Structure and Breakwater, Intitution of Civil Engineer, Thoma Telford, London, Bruce, T., Allop, N.W.. and Pearon, J., 1. Violent overtopping of eawall- extended prediction method, Proc Conf Coatline, Structure and Breakwater, Intitution of Civil Engineer, Thoma Telford, London, Engineering, A.C.o.,. Coatal Engineering Manual. Department of the Army, Waterway Experiment Station, Army Corp of Engineer, Vickburg, Miiippi. EurOtop 7. EurOtop Wave Overtopping of Sea Defence and elated Structure: Aement Manual, Environment Agency (UK), Expertie Netwerk Waterkeren (NL), Kuratorium fr Forchung im Kteningenieurween (DE), Pullen, T., Allop, N.W.., Bruce, T., Kortenhau, A., Schüttrumpf,. and van der Meer, J.W.; Franco, C. and Franco, L., Overtopping formula for caion breakwater with nonbreaking D wave. Journal of Waterway Port Coatal and Ocean Engineering-Ace, 15,, 9-1. Franco, L., de Gerloni, M. and van der Meer, J.W., Wave overtopping on vertical and compoite breakwater. Proceeding of the Coatal Engineering Conference. ASCE, Kobe, Jpn, pp Goda, Y., 195. andom Sea and Deign of Maritime Structure. Univerity of Tokyo Pre, Tokyo. Tai, C.., S.Y. Tzang, S.S. iao, C.C. Cheng and.w. Li, 6. Coatal tructure failure and coatal wave on the north coat of Taiwan due to typhoon erb, Journal of Coatal eearch,,, 9-5. Tzang, S. Y. and S. S. iao, A cae tudy on typhoon-induced conecutive damage on coatal tructure at Keelung Coat. Coatal Structure 99, ASCE, Santander, Spain, Tzang, S. Y., Lin, J.G., iao, S.S.,. Comparion of Coatal Structure Failure Due to Typhoon Kroa and erb in Coatal Water nearby NTOU. Proceeding of th Conference on Ocean Engineering, pp.6-6. (in Chinee) Tzang, S.Y., Ou, S.., Chen, D.W. and o, C.C., 9. Invetigation of Wave Overtopping over Vertical Seawall by Typhoon erb (1996) on Northeatern Coat of Taiwan, Proceeding of 5th International Conference on Aian and Pacific Coat (APAC9), Singapore,, -5.