CHARACTERIZATION OF PHYSICAL ENVIRONMENTAL-FACTORS ON AN INTERTIDAL SANDFLAT, MANUKAU HARBOR, NEW-ZEALAND

Physical environmental factors, including sediment characteristics, in undation time, tidal currents and wind waves, likely to influence the structure of the benthic community at meso-scales (1-100 m) were chara cterised for a sandflat off Wiroa Island (Manukau Harbour, New Zealand ). In a 500x250 m study site, sediment characteristics and bed topogra phy were mostly homogenous apart from patches of low-relief ridges and runnels. Field measurements and hydrodynamic modelling portray a comp lex picture of sediment or particulate transport on the intertidal fla t, involving interactions between the larger scale tidal processes and the smaller scale wave dynamics (1-4 s; 1-15 m). Peak tidal currents in isolation are incapable of eroding bottom sediments, but in combina tion with near-bed orbital currents generated by only very small wind waves, sediment transport can be initiated. Work done on the bed integ rated over an entire tidal cycle by prevailing wind waves is greatest on the elevated and flatter slopes of the study site, where waves shoa l over a wider surf zone and water depths remain shallow enough for wa ve-orbital currents to disturb the bed. The study also provided physic al descriptors quantifying static and hydrodynamic (tidal and wave) fa ctors which were used in companion studies on ecological spatial model ling of bivalve distributions and micro-scale sediment reworking and t ransport. (C) 1997 Elsevier Science B.V.