Hydrodynamics of Manukau Harbour, New Zealand

A calibrated two‐dimensional finite‐element model, which handles flooding/drying of intertidal areas, complemented by field data, has produced information on tidal propagation in Manukau Harbour, New Zealand with reasonably good accuracy. Excluding the upper‐harbour inlets, c. 50% of both the amplification and phase lag in the dominant M 2 tidal constituent occurs through the deep 10‐km‐long entrance channel to Puponga Point. The calculation of tidal residuals has isolated flood‐directed and ebb‐directed residual circulation respectively on either side of Puponga Point, which is a typical pattern for alternating flows around headlands. The model has established the dominance of tidal‐driven over wind‐driven circulation in most of the harbour except in the upper intertidal areas. Wind‐driven circulation in the inner Harbour is characterised by downwind flows over intertidal sand banks with pressure‐driven return flows (vertically averaged) in the deeper main channels. Tidal dissipation rates are sufficiently high to inhibit the onset of any summer stratification.