Wolanski, E., Richmond, R., Davis, G., Bonito, V.

Water and fine sediment dynamics in transient river plumes in a small, reef-fringed bay, Guam

2003

Estuarine, Coastal, and Shelf Science

56

1029-1040

Fouha Bay is a 400-m-long funnel-shaped, 10-m-deep, coral-fringed embayment on the southwest coast of Guam. It drains a small catchment area (5km super(2)) of steeply sloping, highly erodible lateritic soils. River floods are short-lived and the sediment load is very large, with suspended sediment concentration (SSC) exceeding 1000mgl super(-1). The resulting river plume is about 1m thick and is pulsing in a series of 1-2h-long events, with outflow velocity peaking at 0.05ms super(-1). Turbulent entrainment results in an oceanic inflow at depth into the bay. As soon as river flow stops, the plume floats passively and takes 5 days to be flushed out of Fouha Bay. The suspended fine sediment flocculates in 5min and aggregates on ambient transparent exopolymer particles to form muddy marine snow flocs. In calm weather, about 75% of the riverine mud settles out of the river plume into the underlying oceanic water where it forms a transient nepheloid layer. This mud ultimately settles and is trapped in Fouha Bay. Under typhoon-driven, swell waves, the surface plume is at least 7m thick and bottom entrainment of mud results in SSC exceeding 1000mgl super(-1) for several days. It is suggested that successful management of fringing coral reefs adjacent to volcanic islands may not be possible without proper land use management in the surrounding catchment.

River plumes; Catchment area; River basin management; Resuspended sediments; Sediment dynamics; Marine snow; Coral reefs; Floods; Volcanic islands; Turbulent entrainment; Swell; Brackishwater environment; Weather; Nepheloid layer; Sediment load; Resource management; Plumes; Rivers; Suspended Sediments; Entrainment; Coastal Waters; Reefs; River Flow; Corals; Land Use; ISEW; Pacific; Northern Mariana Islands;Guam

10.1016/S0272-7714(02)00321-9

ASFA. FY2002 CRCP Project ID 1011; Project Title: Research to Support Development of Monitoring Technologies and Assessments; Principal Investigator: Ruth Kelty