Hindcasting of Storm Surge by Typhoon 0314(Maemi) in Masan Bay, Korea See-Whan Kang1;Kicheon Jun1; Kwang-Soon Park1; Sung-Dae Han2 1 Coastal Engineering Research Division, Korea Ocean Research and Development Institute Ansan P.O. Box 29, Gyeonggi, Korea e-mail: [email protected] ; [email protected]; [email protected] 2 Department of Civil Engineering, Kyoungnam University 449 Wolyong, Masan, Kyoungnam, Korea e-mail: [email protected] Typhoon 0314(Maemi) landed on the south coast of Korea at 21LST, 12 September, 2003, where its storm surge accompanying with high waves and astronomical high tide induced the most severe coastal disaster in Korea. Especially Masan City facing Masan Bay had the worst damages by the storm-surge flooding with the maximum surge height of ~2.3m recorded at Masan Port. In order to obtain the design surge-heights for the coastal structures in Masan City, a hindcasting study of storm surge for Typhoon 0314 were conducted using a fine-scaled regional surge model which was connected to the larger scaled surge models by a nesting grid system. The sea surface pressure and wind fields were computed by a primitive vortex wind model to obtain the input data for storm surge model simulation. The hindcasted surge heights were compared with the observed surges at Masan Port and also were compared with the surge data recorded at the major tide stations in the south coast of Korea. The result shows that the computed surges were in a good agreement with the observations. Keywords: Typhoon 0314(Maemi), storm surge, coastal disaster, Masan Bay, hindcasting, fine-scaled surge model, vortex wind model 1. INTRODUCTION Typhoon 0314(Maemi) landed on the south coast of Korea at 21LST, 12 September, 2003, where its storm surge accompanying with high waves and astronomical high tide induced the most severe coastal disaster in Korea, causing the loss of 130 lives and the property damage of 4.8 trillion won (~5 billion US dollars) which is the largest disaster since Typhoon Sarah in 1959. Especially Masan City facing Masan Bay had the worst damage by the storm-surge flooding, killing 32 peoples and inflicting severe coastal damage. During the typhoon passage with a central pressure of 950hPa and a progression speed of 45km/hr, the maximum surge height of ~2.3m was recorded at a tide gage of Masan Port. The residential and commercial area facing to the Masan Bay was heavily flooded and the almost underground facilities suffered from the inundation by the storm surge (Yasuda et al 2005). A hindcasting study of storm surge for Typhoon 0314 was conducted by Kawai et al (2004). The hindcasted surges in Masan Bay were much underestimated comparing with observation. In the present study, a hindcasting study of storm surge for Typhoon 0314 were conducted using a fine-scaled regional surge model which was connected to 3 larger different scaled surge models by a nesting grid system. The sea-surface pressure and wind fields were computed by a primitive vortex wind model (Cardone et al, 1992; Kang et al. 2002) for the input data of storm surge simulation. The hindcasted surge heights were compared with the observed surges at Masan Port and also were compared with the surge heights recorded at the tide stations of Yeosu, Tongyoung, Busan and Ulsan in the south coast of Korea. 2. TYPHOON MAEMI AND MASAN BAY 2.1 CHARACTERISTICS OF TYPHOON MAEMI Figure 1 shows the track of typhoon Maemi. Typhoon Maemi was generated on 6 Sep., 2003 at 25°N and 140°E, and moved in the NW direction. Its direction course changed to NNE after passed Miyakojima Island, Okinawa on Sep.11, and approached to Korean Peninsula. The typhoon passed by Jeju Island and landed on the south coast at 21LST, 12 September, 2003. At the landing, the central atmospheric pressure was 950hPa and the progression speed was approximately 45km/h. Then, Typhoon Maemi passed across the Korean Peninsula to East Sea in the early morning on Sep. 13. Fig. 1 Typhoon No. 14 (Maemi) Track 2.2 MASAN BAY Masan Bay is located in about 50km west of Busan as shown in Figure 2, which is a long and slender bay with 2.5km in width and 8km in length, and a bay mouth opens to SSE direction. An average depth of the water in the bay area is about 10 meters. The distance from the Gadeog Channel to Masan Bay mouth is about 25km. It is considered that waves are hard to progress into the bay because the bay mouth is narrower and Masan Port was considered as a good natural harbor. Actually, the Masan Bay had not encountered the damage so far since the opening of Masan Port in a century. An urban area of Masan City lies along the closed-off section of the bay, and harbors are constructed in the coastal area by reclamation. zTid l Fig. 2 Location of the Masan Bay 2.3 OBSERVED WATER-LEVEL DATA While Typhoon Maemi was passing by the southern coast near to Masan Bay, the level of the astronomical tide reached near the high tide of a spring tide. Figure 3 shows the time variation of water level measured at the Masan Port tide station. The tide record indicates that the water-level reached approximately 4.3m above the datum line (chart design level), at which the high tide and the storm surge occurred simultaneously. The astronomical tide level was ~2.0m and then the storm surge deviation became ~2.3m. 6.0 Observed tide (Astro.+Storm Surge) Astronomical tide 5.0 4.0 3.0 (C.D.L., m)(C.D.L., 2.0 1.0 Tide level 0.0 -1.0 -24-18-12-60 6 12182430364248 Time (hr) (9/11/03) (9/12/03) (9/13/03) Fig. 3 Time Variation of Water-Level at the Masan Port Tide Station 3. HINDCASTING OF TYPHOON PRESSURE AND WIND FIELD The sea-surface wind and pressure fields for Typhoon Maemi were hindcasted by using the primitive vortex model (PVM) which was developed by Chow (1971) and modified by Cardone et al. (1992). This model is based on the equation of horizontal motion, vertically averaged through the depth of the PBL. Kang et al. (2002) conducted a comparison study of typhoon wind models for 64 typhoon cases for 1979-1999. In this study the typhoon wind fields were simulated by the both of primitive vortex model (PVM) and typhoon parametric model (TPM). The hindcasted sea-surface winds of the two models were compared with the typhoon winds observed at JMA ocean buoys (22001 and 21002) and Kyushu ocean observation tower. The analysis of RMS and relative errors between hindcasted and observed winds was made to find the accuracy and sensitivity of the typhoon wind models. The hindcasted winds of TPM and PVM both underestimate the observed typhoon winds but PVM winds were much closer to the observations with less RMS and relative errors. To hindcast the pressure and wind fields of Typhoon Maemi, the computational grid of the PVM was used by a moving grid system (Thompson et al. 1996) of rectangular nests, which provides relatively fine grid spacing of 2km near the typhoon inner region and coarse spacing in the outer region. Fig. 4 shows the wind and pressure fields simulated by the PVM wind model for Typhoon Maemi. As shown in Fig. 5, the hindcasted winds were compared with the observed winds at Ieodo Ocean Station during the passage of Typhoon Maemi. They are generally in a good agreement although the hindcasted winds were slightly underestimated in the peak wind region. Typhoon: Maemi(0314) Typhoon: Maemi(0314) Date: 2003/09/12/09(LST) Date: 2003/09/12/15(LST) Vector Scale Vector Scale 40m/s 40m/s Korea Korea Japan Japan 980 980 (a) 2003/09/12 09LST (b) 2003/09/12 15LST Typhoon: Maemi(0314) Typhoon: Maemi(0314) Date: 2003/09/12/21(LST) Date: 2003/09/13/03(LST) Vector Scale Vector Scale 30m/s 40m/s Korea Korea 980 Japan Japan 980 (c) 2003/09/12 21LST (d) 2003/09/13 03LST Fig. 4 Surface Wind and Pressure Fields Simulated by PVM Wind Model 40 38 36 30.0 34 Observed 25.0 Model 32 * . 20.0 . Ieodo . 30 . 15.0 . ... 28 Wind Speed (m/sec) 10.0 . 120 122 124 126 128 130 132 . 5.0 . .. .. 0.0 . 9/11 9/12 9/13 360.0 . Observed . Model . 270.0 .. ... 180.0 Wind Dir. (deg) 90.0 . ...... ....... 0.0 . 9/11 9/12 9/13 September, 2003 Fig. 5 Comparision of PVM Model Wind with Observation at Ieodo Station for Typhoon Maemi 4. STORM SURGE SIMULATION The storm surges during the passage of Typhoon Maemi were simulated by the KORDI's storm surge model (Park et al. 2000) including the terms of the curvature of the earth and Coriolis force, which was established on the spherical coordinate system to cover the whole region of typhoon past tracks. Assuming the vertical acceleration is negligible as if the vertical distribution of currents is uniform, the depth-integrated continuity and momentum equations can be expressed as follows: ∂η 1 ⎡ ∂ ∂ ⎤ + ⎢ ()HU+ () HV cosφ ⎥ = 0 (1) ∂t R cosφ⎣∂ λ ∂φ ⎦ ∂U g ∂η 1 ∂P τ− τ + =Vf − − bλ s λ (2) ∂t R cosφ ∂λ ρR cos φ∂ λ ρH ∂V g ∂η 1 ∂P τ −τ + = −fU − − bφ s φ (3) ∂t R ∂φ ρR ∂ φ ρH Where λ , φ and t are the longitude, latitude and time, respectively. η , U and V are the sea surface elevation, depth averaged velocities.