ABSTRACT

The transport, current and tide equations are solved as a two-dimensional time-dependent non-linear problem in a two layer system. The acceleration and mass transports in the two layers are used to control Kerman-like current profiles. Wave stress as well as wind stress is considered. This is possible because a complete wave spectrum distribution throughout the storm can be calculated and the wave stress computed from it. The wave stress ranges far ahead of the wind field of the storm.

The report is on a practical (but expensive)method of computing storm current profile in locations similar to the Mississippi Delta and an example for that area is given.

The model is compared with simple approximation such as the bath strophic storm tide and the NOAA SPLASH Method. The major difference is the detail of the currents in the horizontal and the tide far ahead of the storm due to wave stress.

Introduction

The ISR Storm Tide Program computes water transports and water surface levels caused by stress and pressure distribution on the water surface, stress between the ocean bottom and the water, and incoming long (tidal) gravity waves. The effect of the rotation of the earth must be included to retain the bath strophic terms in the storm tide description.

In this paper we add the effect of waves tothe storm tide program. We are most interested in hurricane waves and it was impractical to consider wave effects before a spatial distribution spectral components of hurricane waves was available.

Using the notation of Bye (1967), the Stokesmass transport of each wave component is given by:

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being the energy in a certain frequency band and direction band A(J by AS. The total transport is obtained by summing vector ally over e and algebraically over.

In order to take the effect of the Stokes transport Ts into account in storm tide studies, it is convenient to express it in the form of a stress (similar to the wind stress)

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We call T s, defined in this way, the wave stress In addition to the wave stress, there is an additional storm tide term

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which because of order of magnitude is very important to wave induced tides and has less effect related to wind stress. Derivatives of the transport due to winds are small because of the large space scale of the wind field. On the other hand, the derivatives of the wave transport in the direction normal to the sho, re line are large because compared to the winds, the scale of bathymetry over continental shelves is small. This term is most significant in very high waves that lose energy through breaking along the shore. In spIte of their importance we will ignore these terms in this study. Acccrding to Bye, the 10 second period, fully developed sea has a total transport of 1800 feet per second. A hurrica ne can move so tha t this transport builds up in 20 hours. This is equivalent to a T #:, given by a 60 kt. wind. In the example tha tfollows we have the ind stress equivalent to an east wind of 42.2 kts and the wave stress equivalent to a 9 second fully developed sea developing in 20 hours. These stresses are operating on water over uneven bathymetry and shore line.

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