Estuarine forcing of a river plume by river flow and tides
Article first published online: 24 SEP 2008
Copyright 2008 by the American Geophysical Union.
Journal of Geophysical Research: Oceans (1978–2012)
Volume 113, Issue C9, September 2008
How to Cite
2008), Estuarine forcing of a river plume by river flow and tides, J. Geophys. Res., 113, C09033, doi:10.1029/2008JC004844., and (
- Issue published online: 24 SEP 2008
- Article first published online: 24 SEP 2008
- Manuscript Accepted: 30 JUN 2008
- Manuscript Revised: 6 JUN 2008
- Manuscript Received: 31 MAR 2008
- river plumes;
- time series analysis
 Estuarine forcing of a river plume by river discharge and tides is examined with a novel data set capable of characterizing semidiurnal to annual time scales. An instrumented ferry made high-resolution salinity measurements as it crossed the Fraser River plume, British Columbia, Canada, eight times per day over the years 2003–2006. The relative contribution of different forcing factors in controlling the river plume salinity and surface area is examined over the full range of time scales. A Lomb-Scargle periodogram of the plume salinity shows energy concentrated in the semidiurnal and diurnal tidal bands. Diurnal lines contain more energy relative to semidiurnal lines than the respective tidal constituents would suggest. At fortnightly frequencies, local maxima in plume salinity coincide with periods of maxima in daily tidal height, with no phase shift. Thus the estuary adjusts quickly to changes in forcing. The effectiveness of tides in setting the plume salinity is a function of river discharge and is greatest when the river discharge is high and minimal when the river discharge is low. Tidal effects are superimposed onto the long-period river discharge cycle. At time scales of 25 days or longer, the mean river plume salinity decreases quasi-linearly with increasing river discharge, but the change in salinity with river discharge is instantaneous to within the sampling resolution. Plume surface area increases with river discharge, from 200–500 km2 at low river flow to 1000–1500 km2 at high river flow. The magnitude of the surface area is predicted well by scaling the mouth deformation radius.