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engineering numerical modelling

Numerical Modelling of Major Cyclonic Waves and Surge at () since 1945

Dr Sarker, Principal Engineer at Royal strong winds may damage installations, cyclone waves. Given the above risks, Royal HaskoningDHV, highlights the importance dwellings, transportation and communication HaskoningDHV (RHDHV) has developed of considering the impacts of cyclones on systems, trees etc. and cause fires resulting regional tidal hydrodynamic and wave models coastal communities and coastal/marine in considerable loss of life, damage to covering the Northern to structures and facilities… properties and ecosystems. Cyclones also investigate hazards from cyclones and to sup- cause secondary damages such as damages port their project work in the region.The yclones cause significant damage to sea by floating debris, drifted timbers and vessels, models have been used to assess cyclones ports, oil terminals & jetties, offshore sediment erosion and deposition and spreading within this region.This article presents C exploratory drilling rigs, offshore oil of fire. During the last two centuries, tropical numerical modelling results of waves and extraction rigs and various other coastal and cyclones have been responsible for the deaths surge at Duqm in Oman from major cyclones marine structures and facilities.Typical examples of about 1.9 million people worldwide. It is in the Arabian Sea since 1945. of such coastal and marine structures and estimated that 10,000 people per year perish facilities are flood and coast protection due to tropical cyclones. For example, Selection of cyclones for modelling structures, revetments, seawalls, quay walls, Bangladesh is especially vulnerable to tropical Cumulative track map of Tropical Cyclones dykes, retaining structures, piers, breakwaters, cyclones with around 718,000 deaths from in the Arabian Sea from 1970 to 2005 is port and dry dock buildings and facilities, them in the past 50 years.The deadliest illustrated in Figure 1.A total of 29 major ferry terminals, wharf, dolphin, barges, gates, tropical cyclone in Bangladesh was the 1970 cyclones were initially identified to have warehouses, boats, small ships and larger Bhola Cyclone, which had a death toll of crossed the Arabian Sea since 1945 and vessels including cargoes, oil tankers, bulk anywhere from 300,000 to 500,000 lives. affected the Omani coastline.A total of 12 carriers and passenger carriers. Damage due large tidal hydrodynamic model is required to cyclones were selected from this pool of 29 to collision among boats, small ships or larger simulate cyclone surge on a region whereas a cyclones for the study.The 12 selected vessels is common during a cyclone.Very large wave model is required to simulate cyclones are listed in Table 1.Tracks and wind

Table 1: Selected cyclones for modelling

Table 2: Wave conditions generated by the cyclones offshore Duqm

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numerical modelling engineering

Table 3: Maximum surge generated by the cyclones at Duqm coast

and pressure fields of the selected cyclones were obtained from the Joint Typhoon Warning Center (JTWC), USA [http://www.usno.navy.mil/NOOC/nmfc- ph/RSS/jtwc/best_tracks/ioindex.php].

Wind and pressure fields generation The MIKE21 Cyclone Wind Generation Tool of DHI was used to generate the cyclonic Figure 4a: Cyclone 10 waves offshore Duqm wind and pressure fields. Figure 2 shows an example of wind and pressure fields of Cyclone 9 (1998-TC08A).These wind and pressure fields were used to drive the Figure 1: Cyclone tracks in the Arabian Sea from 1970 to 2005 cyclone wave and surge models described later.

Arabian Sea regional models developed by RHDHV The regional wave model Figure 4b: Cyclone 11 waves offshore Duqm RHDHV has developed a two-dimensional Regional Wave Model for the Northern Arabian Sea using the MIKE21 Spectral Wave (SW) software of DHI.The regional model Figure 2a: Wind fields of cyclone 9 (1998-TC08A) covers the coastlines of six countries i.e. Yemen, Oman, UAE, , Pakistan and India (see Figure 3).The regional wave model was used to drive the cyclone wave model to assess cyclone wave conditions within the region. Figure 4c: Cyclone 12 waves offshore Duqm The regional tidal model RHDHV has developed a two-dimensional Regional Tidal Hydrodynamic Model for the Figure 2b: Pressure fields of cyclone 9 (1998-TC08A) Northern Arabian Sea using the MIKE21/3 Flow Model FM software of DHI.The model extent, mesh system and bathymetry are the same as the regional wave model described above. Figure 5: Maximum wave heights offshore Duqm

Cyclone wave modelling simulate the generation and propagation of The regional wave model developed by cyclone waves.The cyclone wave model was RHDHV based on the MIKE21 Spectral Wave driven by wind and pressure fields as shown (SW) Model was used to simulate the in Figure 2. Limited wave data was available cyclone waves.The model was used to Figure 3: Model extent and bathymetry on (2007) and

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engineering numerical modelling

morphological models.

☛ The cyclone wave and surge models are key tools for deriving robust design conditions for coastal and marine structures and facilities.

☛ The models can also provide input conditions to scale physical models for testing structural stability and overtopping rates and input to coastal flood studies.

☛ The model results can be used to drive flood inundation models to predict flood extents and depths.

Although the emphasis has been on Figure 6a: Cyclone 10 surge at Duqm modelling the cyclone wave and surge within the Arabian Sea, the methodology outlined in Cyclone surge modelling this article could be applied to sites within The regional tidal hydrodynamic model other regions that are affected by cyclones. developed by RHDHV based on the MIKE21/3 Flow Model FM was used to Findings simulate the cyclone surge.The cyclone surge The findings from the study may be model was driven by the cyclonic wind and summarised as follows: pressure fields as shown in Figure 2. Limited data on storm surge along the coastlines was ☛ Effects of a cyclone on a site depend on its strength and proximity.A strong cyclone Figure 6b: Cyclone 11 surge at Duqm available to carry out model validation. Cyclone surge at Duqm coast are presented passing far away from a site might generate in Table 3 and in Figures 6 and 7.The highest higher waves and surge than a weaker surge of approximately 1.0 m was found at cyclone passing nearby and vice-versa. the northern part of the Therefore, both strength and proximity during the passage of Cyclone Phet (2010). should be considered in any cyclone study; The model predicted maximum surge of and about 0.41m at Duqm coast during the Cyclone Phet. Cyclone Gonu generated a ☛ Among the 12 cyclones studied, Cyclone maximum surge of 0.20m at Duqm coast. Phet (2010) generated the highest wave Cyclone Nilofar generated a maximum surge height and surge at Duqm. Figure 6c: Cyclone 12 surge at Duqm of 0.17m at Duqm coast.

Application of modelling results “The methodology developed by Royal The results from cyclone wave and surge HaskoningDHV from the study on cyclone models provide valuable information at all modelling in the Northern Arabian Sea could stages of a project including planning, design, be applied to simulate these natural hazards environmental impact assessment, construction, at other sites around the world” operation, and de-commissioning.The model The author would like to results can also be used in emergency thank Royal askoningDHV Figure 7: Maximum surge at Duqm Coast planning and decision-making to estimate (an independent, potential loss of life, damage to properties international engineering (2010).Therefore, the model validation was and marine facilities and to develop rescue and project management focused primarily to these two cyclones. and mitigation measures and plan clean-up consultancy company, Cyclone waves offshore Duqm (19.68°N, operations.The general application of the (www.royalhaskoningdhv.com) for giving 57.93°E) at -23mCD are presented in Table 2 models and the methodology are: permission to publish this article. Please and in Figures 4 and 5. Highest significant contact Dr Mohammad Akhtaruzzaman wave height (of 5.45m) offshore Duqm was ☛ The regional tidal hydrodynamic model Sarker (email: [email protected]) found from Cyclone Phet (2010). Cyclone can be used to simulate tidal movements and for further details on this article including Gonu (2007) and Cyclone Nilofar (2014) surges as well as to drive a wide range of references and for other numerical generated smaller wave heights at this other models such as cyclone, tsunami, oil modelling capabilities of Royal location (i.e. 3.11m and 3.40m respectively). spill, water quality, sediment transport and HaskoningDHV worldwide.

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