Turbidity Maximum Migration and Harbor Siltation in the Tay Estuary

Abstract

Multiboat simultaneous survey along the 50 km macrotidal Tay Estuary suggested that the turbidity maximum was related to resuspension from tidal flats. New monthly analyses revealed that the turbidity maximum varies in position not only with neap/spring tidal cycles but also in response to river runoff. No relationship was found between elemental particle size and aggregate diameter. Both organic and inorganic particles were found to contribute to aggregate growth, the former exhibiting a slightly greater range of particle diameters than the latter. Aggregate diameters increased with suspension concentration and it is suggested that pH as well as salinity also contribute to aggregate formation.Continuous siltmeter recordings at Dundee show maximum suspension concentrations on the ebb phase of neap tides and on spring flood tides. In the lower estuary suspension concentrations and salinities vary from shore to shore. The lateral differences are substantial so that a purely one-dimensional variation pattern does not provide sufficient data for thorough analysis of the processes active in this estuary. The observed behavior of the turbidity maximum and related siltation patterns suggest that concentrating maintenance dredging in late spring and early summer would be cost-effective for Dundee Harbour and similar estuarial situations.Key words: turbidity maximum, suspended sediment, aggregation, estuary, fluvial discharge, harbor siltation