In search of a better sediment mixing coefficient model

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In search of a better sediment mixing coefficient model

1

Introduction

Results of sediment transport calculations are often necessary in solving practical coastal engineering problems. (Sediment transport due to waves and currents). Many transport formulae have been proposed in literature in the past. Selection of the proper one while solving a particular problem, is a difficult task for a coastal engineer.

In considering sediment transport under wave-current conditions it is worthwhile to make a distinction between two situations, viz.:

The fluctuations in the orbital motion have to be fully taken into account in order to find the resulting sediment transport (intra-wave type of description; often: cross-shore sediment transport);

- It is sufficient to take time-averaged effects of the waves into account in order to find the resulting sediment transport rate (intra-wave type of description is not required; often: longshore sediment transport). For the longshore sediment transport mode, transport formulae based on time-averaged velocity distributions and time-averaged sediment concentration distributions over the water depth can often be used, viz.:

h S =

f

z

: sediment transport per unit time and unit width [kg/ms]; : water depth [m];

: time-averaged velocity [m/s]; function ofz;

: time-averaged concentration [kg/m3

]; function ofz;

: vertical ordinate [m]; z = 0 being the bottom. The present paper is restricted to this type of formula.

Although in Eq.(l) the proper description of v(z) over the water depth under waves and current conditions is a far from trivial problem, the present paper refers only to thee(z) distribution.