TRANSVERSE STRUCTURE OF SEMI-DIURNAL CURRENTS OVER A CROSS-SECTION OFTHE MERBOK ESTUARY, MALAYSIA

Measurements are presented of the transverse distribution of longitudi nal semi-diurnal currents over a 900 m-wide cross-section in the seawa rd reaches of the Merbok Estuary, Malaysia. Data from two experiments, one at four stations extending over 31 tidal cycles and the other at nine stations extending over one tidal cycle, showed significant and s ystematic variations in the speeds and phases of the depth-averaged se mi-diurnal currents. A depth-averaged cross-estuary numerical tidal mo del was used to interpret these data. Larger frictional-drag coefficie nts led to somewhat greater damping of modelled currents in the shallo wer water. Smaller drag coefficients led to larger modelled phase vari ations across the estuary. Both modelled and measured longitudinal sem i-diurnal current speeds were strongly dependent on local water depth. Current speeds in the deeper parts of the cross-section were signific antly faster than those in the shallower parts. The modelled and measu red longitudinal, semi-diurnal current phases were such that the times of maximum flood and ebb, and changes of flow direction, occurred ear lier in the shallow waters near the shore, as predicted from theoretic al considerations.