(2013) and Typhoon Agnes (1984) in San Pedro Bay Using the Advanced Circulation Model

NUMERICAL SIMULATION OF STORM SURGES OF TYPHOON HAIYAN (2013) AND TYPHOON AGNES (1984) IN SAN PEDRO BAY USING THE ADVANCED CIRCULATION MODEL

IMEE BREN O. VILLALBA, ERIC C. CRUZ

Institute of Civil Engineering University of the Philippines, Diliman, Quezon City Introduction

19-20 Typhoons passed through the Philippine Area of Responsibility and 8-9 typhoons make landfall annually (Cinco, 2012)

Villalba, Imee Bren O., Cruz, Eric C. Introduction

In 2013, Typhoon Haiyan (Yolanda) struck the Visayas Region and caused catastrophic destruction in Visayas, in which a total of 6,300 individuals were reported dead, 28,688 injured and 1,062 are still missing. Out of the total number of deaths, 93% came from Region VIII where most deaths were due to drowning and trauma.

Track and Intensities of Typhoon Haiyan Introduction

Areas at risk to storm surges were identified but characteristics, behavior, and impact of the natural event were not adequately explained.

People were unable to imagine and visualize the impact of disaster such as that wrought by Typhoon Haiyan (NDRRMC, 2015b)

Villalba, Imee Bren O., Cruz, Eric C. Introduction San Pedro Bay, located in Leyte San Pedro Bay Gulf Frequency of typhoon passing the area is one typhoon annually

Has historical occurrences of storm surges

• Typhoon Haiyan 2013 – 4-6 m storm surge in Tacloban • Typhoon Agnes 1984 – 2-3 m storm surge in Basey • Typhoon 1897 – 4m storm surge in Tacloban

Shallow bathymetry

Villalba, Imee Bren O., Cruz, Eric C. Introduction Objectives of the study This study investigates the storm surge generation in San Pedro bay caused by Typhoon Haiyan (2013) and Typhoon Agnes (1984) using the Advanced Circulation (ADCIRC) model Significance of the Study • to further understand the storm surge generated by Typhoon Haiyan (2013) and Typhoon Agnes (1984) through the use of numerical modelling for disaster prevention management, and preliminary planning and design of coastal structures for disaster mitigation

Villalba, Imee Bren O., Cruz, Eric C. Typhoon Model

Holland 1980 Typhoon Model 퐴 − 푅퐵 Pressure Profile: 푝 = 푝푐 + 푝푛 − 푝푐 푒 푖

0.5 퐵 퐵 푅 푅푚푤 푅2푓2 푅 푓 푚푤 1− 푅 2 푖 푖 Velocity Profile: 푉 = 푒 푖 ∗ 푉푚푤 + − 푅푖 4 2 퐵 퐴 = 푅푚푤 2 푉푚푤 퐵 = 휌 ∗ 푒 1 < B < 2.5 푃푛 − 푃푐

the parameter B defines the shape of the profile and A determines its location relative to the origin.

Villalba, Imee Bren O., Cruz, Eric C. Typhoon Model

Typhoon Data:

Typhoon Haiyan 2013: Joint Typhoon Warning Center (JTWC) best track data

Typhoon Agnes 1984: (Typhoon occurred earlier than 2001) Tack and windspeed from JTWC Central Pressure Data obtained from Japan Meteorological Agency (JMA)

Radius of Maximum Wind speed (Rmw) estimated using Vickery and Wadhera (2008) method

൫3.015−6.29 10−5 훥푝2+0.0337휓 푅푚푤 = 푒

where Δp is the pressure drop and ψ the latitude in degrees

Villalba, Imee Bren O., Cruz, Eric C. Typhoon Model

Central Pressure vs radius of maximum wind (Rmw) of 2013 Typhoon Haiyan, 2008 Typhoon Fensghen, 2006 Typhoon Utor, 2014 Typhoon Hagupit, 2015 Typhoon Melor and 2001 Typhoon Kajiki (taken from JTWC) and computed Rmax using Vickery and Wadhera (2008) method

Villalba, Imee Bren O., Cruz, Eric C. Hydrodynamic Model Set-up

ADCIRC 2DDI Governing Equations – developed by Leuttich and Westerink

Depth-integrated equations of mass and momentum equations 휕휁 휕푈퐻 휕푉퐻 + + = 0 휕푡 휕푥 휕푦

휕푈퐻 휕푈푈퐻 휕푈푉퐻 + + − 푓푉퐻 휕푡 휕푥 휕푦 휕 푝푠 휏푠푥 휏푏푥 = −퐻 + 푔 휁 − 훼휂 + 푀푥 + 퐷푥 + − 휕푥 휌표 휌표 휌표

휕푉퐻 휕푉푈퐻 휕푉푉퐻 + + + 푓푈퐻 휕푡 휕푥 휕푦 휕 푝푠 휏푠푦 휏푏푦 = −퐻 + 푔 휁 − 훼휂 + 푀푦 + 퐷푦 + − 휕푦 휌표 휌표 휌표

Villalba, Imee Bren O., Cruz, Eric C. Hydrodynamic Model Set-up

Model domain

Villalba, Imee Bren O., Cruz, Eric C. Hydrodynamic Model Set-up

Bathymetric data

Digitized bathymetric maps of the National Mapping Resource and Information Authority (NAMRIA) for shallow areas

General Bathymetric Chart of the Oceans (GEBCO) with spatial resolution of 30 arc seconds

Bathymetry of San Pedro Bay

• Depth adaptive triangular mesh

• Smallest grid size of 100 m near the coast

• Maximum grid size of 12 km at the Philippine Trench

• 110,264 elements and 57,736 vertices

• Min elevation of 0.3 m • Max elevation of 9,887.72 m Computational mesh

• Time step: 5 seconds

Open Ocean Boundaries

Pacific Ocean: Leprovost tidal Tacloban Tide database Gaging Station Tidal constituents: M2, S2, K1, O1, P1, Q1

Bohol Sea: Tidal constituents Maasin Station derived from harmonic analysis of WXTide tide at Port Pilar Nasipit Harbor and Maasin stations. Nasipit Harbor

Port Pilar

Nasipit Harbor

Simulated tides using manning’s roughness of n=0.025 and observed tides at Tacloban tide gaging station from Oct. 2-30, 2013

RMSE = 0.1468

Villalba, Imee Bren O., Cruz, Eric C. 2013 Typhoon Haiyan Track of Typhoon Haiyan over Leyte Gulf and time of landfall

Max 10-min sustained windspeed of 110 kts and estimated 910 central pressure 2013 Typhoon Haiyan

Timing of peak water levels and time of inundation • According to interviewed residents, storm surge inundation started after 0730 PHT around Tacloban Port (Tajima et al., 2014)

• In downtown Tacloban, the peak surge occurred around 0800 PHT according to storm chaser Morgerman

• This inundation timing was confirmed by a wall clock in Tacloban City that stopped at 0730 PHT (Switzer et al., 2016) Simulated storm surge hydrograph at Tacloban tide gaging station (orange color) and Tanauan (green color). Date and time are in PHT (UTC+0800)

Timing of peak water levels and time of inundation

• Respondents in Tanauan, Leyte indicated that high water level held for about 30-40 minutes

• In Tanauan, the clock stopped at 0720 PHT (Switzer et al., 2016)

Simulated storm surge hydrograph at Tacloban tide gaging station (orange color) and Tanauan (green color). Date and time are in PHT (UTC+0800)

Tacloban: Simulated peak storm tide is 4-5 meters, which agrees well with observed values of 4-6 meters (Takagi et al., 2014; Mas et al., 2015; Tajima et al., 2014)

Simulated maximum water surface elevation for Typhoon Haiyan (2013)

Simulated maximum water surface profile and observed high water inundation marks from Tajima et al. (2014) along the San Pedro Bay coasts

Ref: Tajima et al., Initial report of JSCE-PICE joint survey on the storm surge disaster caused by Typhoon Haiyan, Coastal Engineering Journal, vol. 56, no. 1, 2014

Villalba, Imee Bren O., Cruz, Eric C. A Study On The Effects Of Historical Typhoon Parameters On Storm Surge Generation In San Pedro Bay Using Advanced Circulation (ADCIRC) Model APAC 2017 Typhoon Agnes (1984) Typhoon Agnes (Local name Undang) passed San Pedro Bay on November 4-5, 1984 (UTC) with a pressure of 940 hPa and a 10-min maximum sustained winds of 105 kts (195 kph). The typhoon had a forward speed of approximately 31 kph and the track of the typhoon (based on JTWC) crossed the San Juanico Strait just north of San Pedro Bay

b c Typhoon Agnes (1984) Poblacion, Basey, Samar Typhoon Agnes (1984) Maximum simulated water surface elevation along the coasts of San Pedro Bay for 1984 Typhoon Agnes Typhoon Agnes (1984)

The maximum storm surge height at Poblacion, Basey is around 2.5 meters, which is consistent with the accounts of the local residents in Basey in which the storm surge rose to around 2-m in height (NDRRMC, 2015) Conclusions

•Numerical modelling using ADCIRC can be an important tool in disaster management, specifically for coastal flooding due to storm surges. •Typhoon Haiyan and Typhoon Agnes have different storm characteristics. The track, high windspeed and forward speed of Typhoon Haiyan have generated high storm surges of about 4-6 meters inside the bay. Typhoon Agnes with a track above San Pedro Bay, a relatively lower windspeed and forward speed than Typhoon Haiyan, have also generated significant storm surges of 2-3 meters inside the bay. •Basey, Samar is considered vulnerable for storm surge for the track of 1984 Typhoon Agnes •Tacloban has the highest storm surge for 2013 Typhoon Haiyan

•The results of this study can be used in the improvement on the knowledge of local storm surge hazard which could be used for information and education campaigns, and planning for storm surge disaster management of the local government along the coasts of San Pedro Bay.

Villalba, Imee Bren O., Cruz, Eric C. A Study On The Effects Of Historical Typhoon Parameters On Storm Surge Generation In San Pedro Bay Using Advanced Circulation (ADCIRC) Model APAC 2017 References

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Villalba, Imee Bren O., Cruz, Eric C.