Pv. Ridd et al., DENSITY-DRIVEN SECONDARY CIRCULATION IN A TROPICAL MANGROVE ESTUARY, Estuarine, coastal and shelf science (Print), 47(5), 1998, pp. 621-632
Observations of suspended sediment concentration (SSC), salinity and c
urrent were made in the Normanby River estuary, Cape York Peninsula, N
orthern Australia. The estuarine reaches are approximately 80 km in le
ngth, and are fringed by mangroves. A well-developed axial convergence
was found to exist almost unbroken for a distance of at least 30 km o
n flood tides, dearly delineated by an accumulation of mangrove leaves
and seed pods on the water surface. The convergence migrated to the i
nside of most bends. Suspended sediment concentration profiles were ve
ry well-mixed both vertically and laterally. Salinity profiles showed
a cross-channel salinity gradient of 0.2/2.5 m, sufficient to form den
sity-driven secondary cells. The cells produce an effective transverse
mixing coefficient of 0.25 m(2) s(-1), of the same order of magnitude
as the conventional transverse diffusion coefficients for natural mea
ndering channels. Mangrove seeds were present in the channel centre du
ring flood tides, and were moved to the channel banks during ebb tides
. Due to the lateral shear in longitudinal currents, mangrove seeds ar
e predicted to move landward up the estuary at a rate of 1 km per day
when density-driven circulation cells are active, influencing mangrove
seed dispersal. (C) 1998 Academic Press.