A two-dimensional bay and river coupled numerical model in Cartesian coordinates was developed to find the impact of the river on the simulated water levels associated with a storm along the coast of Bangladesh. The shallow water models developed for both the bay and river were discretized by the finite difference method with forward in time and central in space. The boundaries for the coast and islands were approximated through proper stair steps representation and solved by a conditionally stable semi-implicit manner on a staggered Arakawa C-grid. A one-way nested scheme technique was used in the bay model to include coastal complexities as well as to save computational costs. A stable tidal condition was made by forcing the sea levels with the most energetic tidal constituent, M2, along with the southern open boundary of the bay model omitting wind stress. The developed model was then applied to foresee the sea-surface elevation associated with the catastrophic cyclone of 1991 and cyclone MORA. A comparative study of the water levels associated with a storm was made through model simulations with and without the inclusion of the river system. We found that the surge height in the bay-river junction area decreased by 20% and the surge height reduced by about 3–8% outside the junction area from this study. The obtained results were found to have a satisfactory similarity with some of the observed data.

No abstract

The similarity law of the wind velocity in wave-overtopping experiments is not known. Then, inthis study, the correspondence of the wind velocity in the wave-overtopping experiments to the one in the real coast was investigated experimentally based on the results of the field observation of wave-overtopping conducted by Fukuda, et al. (1974Fukuda, et al. ( ) in 1971Fukuda, et al. ( -1972 at Niigata east port. Wave-overtopping rate, incident waves, wind direction and wind velocity, etc. were obtained in that observation. The experiments were conducted by using two-dimensional wave tank using the 1/45 reduced scale model. Generating the wave and the wind at the same time, wave-overtopping rates were measured. And the rates in the experiments were compared with the ones of the field observation. It was found that the wind velocity in the experiment becomes about 1/3 of the wind velocity of the real coast.

Frequency downshift of gravity wave spectra in deep and finite water depths due to the nonlinear energy transfer are discussed. In deep water depths, numerical computationes of the nonlinera energy transfer are performed with DIA (Hasselmann et al., 1985), RIAM (Komatsu et al., 1993) and SRIAM (Komatsu et al., 1996). Then, differences in temporal changes of directional spectra computed with a modified WAM implemented with RIAM and SRIAM are compared with those computed with the original WAM implemented with DIA. In finite water depth, numerical computations are performed with a modified WAM implemented with FD-RIAM (Hashimoto, et al., 2002), an exact method, which was upgraded from an earlier version (Hashimoto et al., 1998) based on Komatsu et al., (2001). Differeces in frequency downshift of gravity wave spectra in deep and finite water depths are discussed based on the numerial results for various directional spectra in various water depths.

No abstract