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Abstract(s)
The exchange (import, export) of sediment near the mouth of the Guadiana Estuary during periods of damregulated
and non-regulated river flow are computed and compared. Bedload and suspended sediment transport
rates were derived from Acoustic Doppler Profiler (ADP) measurements at a fixed station (~2 years) and across
the estuarine channel (3 tidal cycles). Suspended sediment concentrations (SSC) were obtained from water
sampling during one of the tidal cycle surveys, and from turbidity measurements used to calibrate the ADP echo
level at the fixed station. For low river flows, the net bedload transport was down-estuary at springs, yielding an
estimate of 5,400 m3
yr-1
of export seaward. The vertical shear was enhanced for higher river flows, and favoured
the upstream currents near the bed. Hence, the sand transport rates were similar to those predicted for low river
flows. Significantly larger volumes of sand are exported only if the river discharge is large enough for freshwater
to occupy the entire estuary. For low river flows, suspended sediment was imported at neaps and exported at
springs, and the net transport was balanced over the long term. Significant export took place during moderately
high discharge events. However, the transport of suspended sediment was several orders of magnitude lower than
before flow regulation.
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Coastal Education and Research Foundation