Hydrodynamics and equilibrium sediment dynamics of shallow, funnel-shaped tidal estuaries

CT Friedrichs*, BD Armbrust, HE de Swart

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference contributionAcademicpeer-review


Observations of tidal and sediment properties available for the River Tamar are used to guide perturbation solutions for hydrodynamics and equilibrium sediment dynamics. For net sediment transport, important contributions to velocity at O(epsilon) are flood dominance due to internally generated nonlinearity and ebb dominance due to river flow. The advection-dispersion equation is used to solve for tidal variations in depth-integrated suspended sediment concentration. The lowest order balance is between erosion and deposition; the importance of advection is scaled by the ratio of the sediment response time-scale to the tidal time-scale. Analytical solutions show that tidally averaged sediment transport at O(epsilon) is due to three dominant effects: (i) flood-dominant tidal asymmetry, (ii) seaward river flow, and (iii) settling/scour lag made effective by along-channel width convergence. The third effect represents a new mechanism for the maintenance of the turbidity maximum. Unlike previous solutions applied to short tidal estuaries of constant width, variation in tidally averaged channel depth is not found to be an important control. Assuming uniform bed erodability, the predicted change in direction of tidally averaged sediment transport coincides with the observed location of the turbidity maximum in the River Tamar. However, an equilibrium sediment budget requires erodability to vary along-channel. An analytical solution is presented for along-channel variation in bed erodability which produces zero net transport of sediment at O(epsilon). By assuming a migrating, finite size pool of easily erodable bed sediment, analytical solutions successfully reproduce the along-channel extent and intensity of the high turbidity region along the River Tamar, as well as its response to variations in fresh water discharge.

Original languageEnglish
EditorsJ Dronkers, M Scheffers
Place of PublicationLEIDEN
PublisherA.A. Balkema Publishers
Number of pages13
ISBN (Print)90-5410-965-3
Publication statusPublished - 1998
Event8th International Biennial Conference on Physics of Estuaries and Coastal Seas - THE HAGUE, Netherlands
Duration: 9 Sept 199612 Sept 1996


Conference8th International Biennial Conference on Physics of Estuaries and Coastal Seas


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