Salinity Intrusion In The Fly River Estuary, Papua New Guinea
Intensive field and model studies were undertaken into the dynamics of the Fly River estuary, Papua New Guinea. The estuary has three dominant channels forming a shallow, fan-shaped delta, and receives a mean freshwater discharge of approximately 6,000 m3s-1 with little seasonal variation. The estuary is vertically well-mixed in salinity by strong tidal currents. The saline water is distributed unevenly between the channels. Model studies verified by field data suggest that this due to the dynamics of the estuary which are controlled by shallow water frictional effects that generate higher tidal harmonics, the shoaling of the tidal wave from the funnel shape of the estuary, a low value of the bottom friction coefficient resulting from the presence of fluid mud, and the along-channel water surface gradient. This gradient is in turn controlled by two dominant forcings, namely the freshwater discharge and the dominant offshore trade wind. This gradient is also modulated by the spring-neap cycle of the tidal currents which controls the low-frequency friction coefficient. The absence of strong cross-channel salinity gradients and of axial convergence zones is attributed to enhanced horizontal mixing by the lateral velocity shear due to the sinuosity of the thalweg meandering between numerous islands and shoals.