TY - JOUR
T1 - Hydrodynamic and geomorphological controls on suspended sediment transport in mangrove creek systems, a case study
T2 - Cocoa Creek, Townsville, Australia
AU - Bryce, S.
AU - Larcombe, P.
AU - Ridd, P. V.
N1 - Funding Information:
Many thanks go to Ross Hyne for assistance with fieldwork, and loan of a boat, vehicles and other field equipment. Thanks are also due to Mick Fitzpatrick from the Townsville Port Authority for access to tidal data, Russell Jaycock from the Bureau of Meteorology for the wind data and Gregg Brunskill of the Australian Institute of Marine Science for access to AUSLIG topographic maps. This work was funded by an ARC Large Grant to P.L. and P.V.R., and by James Cook University. The two anonymous journal reviewers are thanked for their helpful comments in improving the manuscript.
PY - 2003/3/1
Y1 - 2003/3/1
N2 - In tide-dominated sedimentary systems, close relationships exist between tidal hydrodynamics, sediment transport and geomorphology. Tropical coastlines contain many tide-dominated mangrove creeks, yet few studies to date have examined the detail of such relationships for these environments. Time-series observations of tidal height, currents and suspended sediment concentrations were taken between 1992 and 1996 in Cocoa Creek, a mangrove creek system near Townsville, NE Australia. The creek and surrounding mangrove swamps and salt flats were surveyed with an echo-sounder and total survey station, respectively. For 'within-channel' tides, the flood tide is always the fastest, at up to 0.5 ms-1. In contrast, for overbank tides (i.e. tidal height >+1.5 m Australian Height Datum, AHD) ebb currents are fastest in July, December and January, but flood currents are fastest in August and September, at up to 1 m s-1 in both cases. The tidal asymmetry of overbank tides in Cocoa Creek is controlled by the interaction between offshore tidal forcing and the intertidal storage effect of the mangrove swamps and salt flats, with the result being that during certain periods of the year there tends to be a predominance of either faster flood or ebb velocities on overbank tides. Significant tidal suspended sediment transport in the channel is only initiated at overbank height. On overbank tides, measured net suspended sediment fluxes in the channel are mostly seaward-directed (up to 180 t per tidal cycle). However, the net flux measured over a neap-spring period may be either landwards or seawards (up to 465 and 60 t, respectively). Furthermore, on the larger overbank tides (where the maximum tidal height >+1.85 m AHD) net sediment fluxes may be reduced because of a limited supply of available material. Thus hydrodynamic and sediment sampling durations of up to a month may not be representative of long-term trends. Given that our large dataset has not identified a clear long-term net transport direction within the creek system, we conclude tentatively that the geomorphology of Cocoa Creek may be near a long-term equilibrium.
AB - In tide-dominated sedimentary systems, close relationships exist between tidal hydrodynamics, sediment transport and geomorphology. Tropical coastlines contain many tide-dominated mangrove creeks, yet few studies to date have examined the detail of such relationships for these environments. Time-series observations of tidal height, currents and suspended sediment concentrations were taken between 1992 and 1996 in Cocoa Creek, a mangrove creek system near Townsville, NE Australia. The creek and surrounding mangrove swamps and salt flats were surveyed with an echo-sounder and total survey station, respectively. For 'within-channel' tides, the flood tide is always the fastest, at up to 0.5 ms-1. In contrast, for overbank tides (i.e. tidal height >+1.5 m Australian Height Datum, AHD) ebb currents are fastest in July, December and January, but flood currents are fastest in August and September, at up to 1 m s-1 in both cases. The tidal asymmetry of overbank tides in Cocoa Creek is controlled by the interaction between offshore tidal forcing and the intertidal storage effect of the mangrove swamps and salt flats, with the result being that during certain periods of the year there tends to be a predominance of either faster flood or ebb velocities on overbank tides. Significant tidal suspended sediment transport in the channel is only initiated at overbank height. On overbank tides, measured net suspended sediment fluxes in the channel are mostly seaward-directed (up to 180 t per tidal cycle). However, the net flux measured over a neap-spring period may be either landwards or seawards (up to 465 and 60 t, respectively). Furthermore, on the larger overbank tides (where the maximum tidal height >+1.85 m AHD) net sediment fluxes may be reduced because of a limited supply of available material. Thus hydrodynamic and sediment sampling durations of up to a month may not be representative of long-term trends. Given that our large dataset has not identified a clear long-term net transport direction within the creek system, we conclude tentatively that the geomorphology of Cocoa Creek may be near a long-term equilibrium.
KW - Australia
KW - Mangroves
KW - Sediment transport
KW - Tidal creek
UR - http://www.scopus.com/inward/record.url?scp=0038661639&partnerID=8YFLogxK
U2 - 10.1016/S0272-7714(02)00192-0
DO - 10.1016/S0272-7714(02)00192-0
M3 - Article
AN - SCOPUS:0038661639
SN - 0272-7714
VL - 56
SP - 415
EP - 431
JO - Estuarine, Coastal and Shelf Science
JF - Estuarine, Coastal and Shelf Science
IS - 3-4
ER -