Abdalazeez, Ahmed

Barthel, Knut

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Conference Paper, Published VersionAbdalazeez, Ahmed; Barthel, KnutEstimation of Wave Run-up in the Northern Indian Oceanusing WAM modelZur Verfügung gestellt in Kooperation mit/Provided in Cooperation with:Kuratorium für Forschung im Küsteningenieurwesen (KFKI)Verfügbar unter/Available at: https://hdl.handle.net/20.500.11970/99454Vorgeschlagene Zitierweise/Suggested citation:Abdalazeez, Ahmed; Barthel, Knut (2014): Estimation of Wave Run-up in the Northern IndianOcean using WAM model. In: Lehfeldt, Rainer; Kopmann, Rebekka (Hg.): ICHE 2014.Proceedings of the 11th International Conference on Hydroscience & Engineering. Karlsruhe:Bundesanstalt für Wasserbau. S. 385-390.Standardnutzungsbedingungen/Terms of Use:Die Dokumente in HENRY stehen unter der Creative Commons Lizenz CC BY 4.0, sofern keine abweichendenNutzungsbedingungen getroffen wurden. Damit ist sowohl die kommerzielle Nutzung als auch das Teilen, dieWeiterbearbeitung und Speicherung erlaubt. Das Verwenden und das Bearbeiten stehen unter der Bedingung derNamensnennung. Im Einzelfall kann eine restriktivere Lizenz gelten; dann gelten abweichend von den obigenNutzungsbedingungen die in der dort genannten Lizenz gewährten Nutzungsrechte.Documents in HENRY are made available under the Creative Commons License CC BY 4.0, if no other license isapplicable. Under CC BY 4.0 commercial use and sharing, remixing, transforming, and building upon the materialof the work is permitted. In some cases a different, more restrictive license may apply; if applicable the terms ofthe restrictive license will be binding. 1 INTRODUCTION The vertical displacement in wave runup consists of two components: Elevation of the mean water level above the still water level, which is called the wave setup, and the fluctuations of that mean, which is called the swash (Ruggiero et al., 2004), the swash is given at times of extrema and the difference be-tween the runup and the setup values. Based on statistics, extreme wave runup R2 is the value of R that will be exceeded 2% of the time. The lowest vertical displacement below the still water level is called wave rundown (Gourlay, 1992). 1.1 The area of study The North Indian Ocean covers two interacting regions affected by wave climate: 1. The Equatorial region that extents to about 5 to 8ºN, which is dominated by local wind forcing. 2. The Arabian Sea, which is dominated by strong southwesterly winds blowing during the summer mon-soon (Kantha et al., 2008). The locations at which the runup wave study will be focused. At each location, a statistical analysis of extreme wave runup is made, which is based on 21 years of six-hourly wave height and period data. The locations were selected because of their small beach slopes in order to inves-tigate the condition of the ratio (ξ), of beach slope to square root of wave steepness which must be smaller than 0.3 to be considered as a dissipative wave runup. Google Earth was used to get the beach slope (β). Then tan β (see Table 1) was calculated. The beach slope for Maldives is considered as an imaginary beach since where we were not able to use this method to estimate its beach slope. According to Riyaz (2009), the Maldives islands are small and rarely reach more than 2.5 m above sea level, therefore, they are at risk of flooding, tsunamis, and sea level changes. Estimation of Wave Run-up in the Northern Indian Ocean using WAM model A.A. Abdalazeez Institute of Marine Research, Portsudan, Sudan B.K. Barthel Geophysical Institute, Bergen, Norway  ABSTRACT: The aim of this study is to estimate the wave runup on selected beaches around the northern Indian Ocean. The runup has been estimated using ERA-Interim, which is the latest global atmospheric re-analysis produced by the European Centre for Medium-Range Weather Forecasts (ECMWF). ECMWF uses the global Wave Model (WAM) model to calculate two dimensional wave spectra. The distances be-tween the model grid points and the beaches have been calculated by a great circle calculator. The beach slopes have been calculated by Google Earth for all locations, except Maldives beach, which was as-sumed as an imaginary beach because the method of calculating the slope could not be used there. The significant wave height as well as the peak wave period at the grid points is assumed to be the same at the beach. The most frequent estimated runup is between 0.5 m and 1.0 m, which is produced by swell com-ing from the southern Indian Ocean for all locations except Sri Lanka, India and Maldives shores, where the most frequent runup value is less than 0.5 m. Generally, the largest wave heights are wind sea and the longest wavelengths are swell. The mean elevation of the runup for all locations is 56 cm. It is compara-ble to the measured values obtained by (Stockdon et al., 2006) at several beaches in USA and the Nether-lands who found the mean value of dissipative sites to be 84 cm for all experiments. Keywords: wave runup, Swell, Wind speed, Northern Indian Ocean ICHE 2014, Hamburg - Lehfeldt & Kopmann (eds) - © 2014 Bundesanstalt für Wasserbau ISBN 978-3-939230-32-83852 DATA AND METHODS The data of wave height, the period and the surface wind have been collected from seven grid point loca-tions near shores in the northern Indian Ocean. The wave height and period values are combined for swell and wind sea. The total wave height is the square root of the sum of the squares of the separate trains: Htotal =  √𝐻2𝑠𝑤𝑒𝑙𝑙 + 𝐻2𝑤𝑖𝑛𝑑 The corresponding shore points (beaches) are selected because they represent different locations and dif-ferent gentle beach slopes, except the beach on the Maldives, which is assumed as an imaginary beach. The dataset in this study by ERA-Interim, which is the latest global atmospheric re-analysis produced by the European Centre for Medium-Range Weather Forecasts (ECMWF) in collaboration with many insti-tutions.  The ERA-Interim software covers the period from 1 January 1989 until 31 December 2009 every six hour. The analysis provides the global surface wind, and the two wave parameters significant height and peak period (Kulseng, 2010). The horizontal resolution of the wave model in ERA-Interim is 110 km (Dee et al., 2011).   Table 1. Name of beaches locations, its latitude and longitude, the slope of the beaches, the directions of the beaches, model grid point position (latitude and longitude), the corresponding wave forecasting distance from grid points to the beaches, and direction from beaches to the grid points, this table contain for all location except Maldives beach is just an imaginary beach. Location Lat/Long beach Beach slope Exposure Lat/Long grid points Distance km Direction to grid points Oman 18o41'57" 56o45'08" 0.23 E 18.5N 57.0E 34 SE Somalia 5o23'12" 48o33'35" 0.46 E 0.5N 49.0E 65 SE Sri Lank 7o47'16" 81o38'37" 0.23 NE 8.0N 81.5E 28 NW Goa 15o14'34" 73o55'21" 2.30 W 14.5N 74.0E 82 S India 19o53'11" 72o40'54" 2.30 W 20.0N 27.5E 22 NW Pakistan 25o28'03" 66o18'02" 0.29 S 25.0N 66.0E 60 SSW  2.1 Wave runup equation The vertical displacement in wave runup R2 consists of two components Wave setup <η˃ and Swash S:  R2 = <η˃ + S/2  (1)  Where swash S = (Sinc 2 + SIG 2)0.5   A better linear relation that combines <η˃ + S/2 and R2 has been derived from Stockdon’s et al (2006) experiment. Then the Equation (1) becomes  R2 = 1.1 (<η˃ + S/2)  (2)  When the Irribaren number, ξₒ ˃ 0.3, then the general formula of non-dissipation wave runup has been written as  R2 = 1.1(0.35 βf(HₒLₒ)1/2 + [HₒLₒ(0.56 βf2 +0.004)]1/2/2) (3)  When ξₒ < 0.3 the dissipative runup may be calculated as   R2 = 0.043(HₒLₒ)1/2 (4) 3863 RESULTS 3.1 Frequency distribution of runup The frequency distribution of the estimated runup at the shore in Oman (Figure 1a) reveals that in 49% of the cases the runup is between 0.5m and 1.0m, while the highest number of cases of wave runup at the shore in Somalia, 66%, occurs between 0.5m and 1.0m (see Figure 1b). At Sri Lanka shore, Figure 3c shows that in most cases, 52%, wave runup is less than 0.5m. The estimation of wave runup at the shore in Goa reveals that 71% occur between 0.5 and 1.0m. At the shore in India, Figure 1d, most number of cases, 59%, runup is less than 0.5m. While at the shore in Pakistan, Figure 1e shows that 53% of the cases runup is between 0.5 and 1.0m. Figures 1g1 and 1g2 demonstrate that at an imaginary dissipative beach when the Iribarren number ξ < 0.3 in Maldives 58% of the cases runup is less than 0.5m, while on a non-dissipative beach with the Iribaren number equal to 0.3. 58% of the cases runup is between 0.5 and 1.0m.  Summary: Generally the highest number of cases of estimated wave runup lies between 0.5m and 1.0m for all locations except Sri Lanka, India and Maldives (dissipative runup) shores where it is less than 0.5m (see Figures 1e and 1g).     387    Figure 2. Wave runup as a function of wave height and wave length at: (a) Oman, (b) Somalia, (c) Sri Lank, (d) Goa, (e) India, (f) Pakistan and (g) Maldives. The contour lines are given by the runup formula for dissipative beaches. 4 DISCUSSION The frequency distributions of estimated wave runup at the shores reveal that more than half of the time runup is less than 0.5–0.75m. Wave height values become higher at high latitudes (Oman, Pakistan, and Goa) and decrease towards the Equator (Sri Lanka, Maldives and Somalia). The highest runup is generated at medium wind speed. This suggests that swell strongly contributes to generate extreme runup. The methods, which we have used, contain some uncertainty because we do not involve the wind direction; we just assume that the wave height and the period at the grid point are the same at the beach. We also neglected the tidal effect. We assumed that the slope is not changing from sea to the beach. We took the imaginary beach slope in Maldives at two cases investigating two conditions: Dissipative, when the Iribarren number is less than 0.3, and a non-dissipative beach with Iribarren number equal to 0.3.  5 CONCLUSION We estimated runup on gentle beaches for seven locations in the northern Indian Ocean covering the peri-od from 1 January 1989 to 31 December 2009 every six hour. The most frequent estimated wave runup ranges between 0.5 and 1.0 m. In general, long swell is the dominant factor of runup. The wave height depends on locations, it increases with latitude. 389REFERENCES Dee, D.P., Uppala, S.M., Simmons, A.J., Berrisford, P., Poli, P., Kobayashi, S., Andrae, U., Balmaseda, M.A., Balsamo, G., and Bauer, P. (2011). The ERA– Interim reanalysis: Configuration and performance of the data assimilation system. Quar-terly Journal of the Royal Meteorological Society, 137(656):pp. 553– 597. Gourlay, M.R. (1992). Wave set-up, wave run-up and beach water table: Interaction between surf zone hydraulics and groundwater hydraulics. Coastal Engineering, 17(1–2):pp. 93–144.  Kantha, L., Rojsiraphisal, T., and Lopez, J. (2008). The North Indian Ocean circulation and its variability as seen in a numeri-cal hindcast of the years 1993– 2004. Progress in Oceanography, 76(1):pp. 111–147.  Kulseng, R. (2010). 100–year waves in the Mozambique Channel. Master’s thesis, University of Bergen, Geophysical Institute, 68 pp.  Riyaz, A. (2009). The Information Culture of the Maldives: An Exploratory Study of Information Provision and Access in a Small Island Developing State. Master’s thesis, Curtin University of Technology.  Ruggiero, P., Holman, R.A., and Beach, R.A. (2004). Wave run-up on a highenergy dissipative beach. Journal of Geophysical research, 109(C06025):pp. 1–12.  Stockdon, H.F., Holman, R.A., Howd, P.A., and Sallenger, A.H. (2006). Empirical parameterization of setup, swash, and runup. Coastal Engineering, 53(7):pp. 573–588. 390

Estimation of Wave Run-up in the Northern Indian Ocean using WAM model

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Estimation of Wave Run-up in the Northern Indian Ocean using WAM model

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