NorCal Open Access Publications Journal of Environmental Science and Allied Research Volume 2019; Issue 03 M A Sarker Review Article Numerical Modelling of Storm Surge from the 1991 Cyclone in the Bay of Bengal (Bangladesh) by Royal HaskoningDHV M A Sarker* Royal HaskoningDHV, Rightwell House, Bretton, Peterborough, United Kingdom *Corresponding author: M A Sarker, Royal HaskoningDHV, Rightwell House, Bretton, Peterborough, PE3 8DW, United Kingdom, Tel: +44 (0)1733 336556; E-mail: [email protected] Received: 15 June, 2019; Accepted: 30 October, 2019; Published: 05 November, 2019 Abstract Introduction Cyclone modelling results are used to derive robust Cyclones (also known as hurricanes or typhoons) need design conditions for coastal and marine structures and favourable conditions to form such as a) warm sea surface facilities. Cyclone modelling results are also used for temperature b) large convective instability c) low level emergency planning and decision-making to estimate positive vorticity d) weak vertical wind shear of horizontal potential loss of life, damage to properties and marine wind and e) Coriolis force. Cyclones require ocean facilities and to develop rescue and mitigation measures and temperatures of at least 26.5°C for their formation and plan clean-up operations. Royal HaskoningDHV (hereafter growth through a relatively deep layer (~50m). Cyclones are associated with steep pressure gradients and consequently RHDHV) has set up regional tidal hydrodynamic and wave generate strong winds and storm surges. The destruction generation/transformation models covering the Bay of from a cyclone depends on its intensity, size and location. Bengal and its surrounding areas to address the above Cyclones generate high winds, waves, water levels (surge) and are associated with intense rainfall. in the Bay of Bengal affecting the Bangladeshi coastline since 1945.issues. The A long 1991 list Cyclone of major (22-30 cyclones April was 1991) initially was identified found to be the second strongest cyclone affecting the coastal areas properties, ecosystems and marine structures and facilities. Cyclones cause significant loss of life and damage to of Bangladesh since 1945 (after the Bhola Cyclone on 7-13 Heavy and prolonged rains associated with cyclones November 1970). As less information is available on the landslides causing loss of life and property. The generation 1991 Cyclone, this paper has concentrated on this event ofcause large floods waves of andlow-lying high-water areas andlevels lead result to mudslides in damage and to to illustrate the use of numerical modelling technique to coastal and offshore structures. simulate storm surge generated by cyclones. The MIKE21 Flow Model developed by DHI was used in the study. During the last two centuries, cyclones have been Sample results of storm surge from the modelling study are responsible for the deaths of about 1.9 million people presented in this paper for illustration purposes. Structural worldwide [1]. It is estimated that 10,000 people per design considerations and cyclone risk reduction measures year perish due to cyclones [1]. Bangladesh is especially vulnerable to cyclones with around 718,000 deaths in the are also discussed. The model could be used to simulate any past 50 years [2]. The deadliest cyclone in Bangladesh was cyclone generated anywhere within the Bay of Bengal and the 1970 Bhola Cyclone, with a death toll of up to 500,000 its surrounding areas. The methodology described in this [3]. At least 138,000 people were killed and as many as 10 paper for modelling cyclone surge in the Bay of Bengal could million people became homeless during the 1991 Cyclone in also be applied to simulate cyclones at other sites around the Bangladesh [4]. world. Despite their devastating effects, cyclones are essential Keywords: Numerical modelling; Natural hazards; to the Earth’s atmosphere as they bring rain to dry areas and Cyclones; Storm surge; Port development; Bay of Bengal; transfer heat and energy between the equator and the cooler 1991 Cyclone. regions nearer the poles. 01 Citation: M A Sarker (2019) Numerical Modelling of Storm Surge from the 1991 Cyclone in the Bay of Bengal (Bangladesh) by Royal HaskoningDHV. J Environ Sci Allied Res 2019: 109-116. The objective of the paper is to provide improved and to extract model results anywhere within the wider region. comprehensive model results (both positive and negative Cyclones can result in negative surges (reduction in water surges) to researchers and practitioners over a wider depth) which can affect the operation of coastal facilities and region. These results are useful for deriving robust design ports. Therefore, maximum negative surges are provided conditions for coastal and marine structures and facilities. along with a two-dimensional plot showing values over a The results are also valuable in estimating potential loss of wider region. life, damage to properties and marine facilities, to develop The Bay of Bengal is a potentially energetic region for rescue and mitigation measures and to plan clean-up the development of cyclonic storms accounting for about operations. Structural design considerations and cyclone 7% of the global annual total number of tropical storms [6]. risk reduction measures are also provided. Historical cyclone tracks in the Bay of Bengal by monthly occurrence during 1877-2010 were obtained by RHDHV the Bay of Bengal since 1970. The 1991 Cyclone (22-30 April for a project in the east coast of India from the Indian 1991)Royal was HaskoningDHV found to be the has second identified strongest 14 major cyclone cyclones affecting in Meteorological Department [7] as presented in Table 1. the coastal areas of Bangladesh since 1970 (after the Bhola A total of 14 major cyclones have affected the Bay of Cyclone on 7-13 November 1970). Numerical modelling of Bengal since 1970 as shown in Table 2. surge from this 1991 cyclone is reported in this paper. Data in Table 2 for Cyclone 1 was obtained from [3] The latest version of the MIKE21 software (2019 version) whereas data for Cyclone 10 was obtained from IMD was used which enabled the application of the latest technical [7] where 3-minutes mean wind speed of 102 knots advancement [5]. Generally, a spectral wave model is run was converted to 1-minute mean of 112 knots using the methodology from [8]. Data in Table 2 for the remaining the present study, the wave and tidal modelling were carried cyclones were obtained from the Joint Typhoon Warning outfirst simultaneously to derive radiation in a coupledstress to mode input where into a thetidal tidal model. model In Center (JTWC), USA [9]. obtained the necessary radiation stress directly from the The monsoon season in the Bay of Bengal is from June to wave model and thereby improved the accuracy of the September. Cyclones of the pre-monsoon and post-monsoon model prediction. The use of powerful computers allowed seasons are the most destructive due to greater instability in the atmosphere and the weak vertical winds. They generally in simulation results. Besides the model results at selected form over the Andaman Sea or south-east of the Bay of keythe adoptionlocations, of two-dimensional fine model mesh/grid plots ofto modelimprove results accuracy are Bengal. They initially move to west or north-west and then provided in the paper to allow researchers and practitioners to north and finally to north-east across Bangladesh. Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 7 2 2 23 75 104 142 177 158 156 109 38 Table 1: Monthly occurrence of historical cyclones in the Bay of Bengal during 1877-2010 [7]. Time & Date Maximum 1-minute mean Minimum central Radius of No. Year Codes &Names sustained wind speeds pressure maximum Start End (knots) (hPa) wind speeds (nm) 1 1970 Bhola Cyclone 07/11/1970 18:00 13/11/1970 00:00 130 960 N/A 2 1972 TC 14B 15/11/1972 06:00 23/11/1972 00:00 90 N/A N/A 3 1975 TC 02B 01/05/1975 00:00 11/05/1975 12:00 95 N/A N/A 4 1977 TC 05B 09/11/1977 00:00 23/11/1977 00:00 110 N/A N/A 5 1977 TC 06B 14/11/1977 00:00 20/11/1977 12:00 110 N/A N/A 6 1982 TC 01B 30/04/1982 06:00 05/05/1982 12:00 120 NIA N/A 7 1988 TC 04B 21/11/1988 18:00 30/11/1988 00:00 110 N/A N/A 8 1990 TC 02B 03/05/1990 12:00 11/05/1990 06:00 125 N/A N/A 9 1991 TC 02B (BoB 01) 22/04/1991 18:00 30/04/1991 18:00 140 N/A N/A 10 1992 BoB-8 16/11/1992 06:00 21/11/1992 18:00 112 952 N/A 11 1994 TC 02B 26/04/1994 18:00 03/05/1994 12:00 125 N/A N/A 12 1999 TC 05B 25/10/1999 00:00 03/11/1999 06:00 140 N/A N/A 13 2013 TC 02B (Phailin) 07/10/2013 12:00 13/10/2013 12:00 140 918 10 TC 03B 14 2014 06/10/2014 06:00 13/10/2014 12:00 115 937 10, 15 (Hudhud) Table 2: Major Cyclones in the Bay of Bengal since 1970. J Environ Sci Allied Res 2019: 109-116. 02 Citation: M A Sarker (2019) Numerical Modelling of Storm Surge from the 1991 Cyclone in the Bay of Bengal (Bangladesh) by Royal HaskoningDHV. J Environ Sci Allied Res 2019: 109-116. from cyclone data. Several cyclone parametric models Storm (BOB 01) by IMD [7] and as Category 5 Cyclone are included in the tool including Young and Sobey model (02B)The by 1991 JTWC Cyclone [9].