As part of the sustainable management of the Port of Saint John there is a critical
need to maintain sufficient under keel clearance for the various container and cruise ship traffic in and out of the harbour. Because of high and variable sedimentation rates,
annual maintenance dredging is necessary and causes economic concerns for the Port.
Therefore to better predict future dredging volumes and hence improve the budgeting
process for the Port of Saint John, the estuarine circulation of the harbour has been
analysed to better quantify the relative importance of the offshore sediments that
contribute to the high dredging volumes in the Saint John harbour.
The Port of Saint John lies at the mouth of the Saint John River on the north side
of the macrotidal Bay of Fundy. Because of this, the harbour sedimentation is influenced
by two major sources of siltation: the Saint John River and the Bay of Fundy. The
sediment flux from the river is strongly modulated by the seasonal variations in river
discharge. In the Bay of Fundy, there is significant resuspension of offshore marine
sediments.
To better understand this complex interaction between the fresh water flow and
the tidal inflow of salt water, high density oceanographic surveys have been conducted
at four different river discharge periods. In order to quantitatively analyse the mixing of
the fresh and salt water in the harbour channels, high density ADCP currents and CTD
measurements were acquired along main longitudinal axis of the Main Harbour channel and Courtenay Bay over four tidal cycles. By imaging the 200kHz acoustic volume backscatter within the water column, the appearance of interfacial waves at the pycnocline can be examined. The optical backscatter sensor provided observations used to estimate suspended sediment concentrations.
A cross-sectional analysis of the flow at a location 700m south and seaward of
the Rodney bay terminal in the Main Channel revealed that regardless of the river
discharge rate, the interfacial waves are best developed on the rising tide. However,
during the Spring freshet the interfacial waves are also developed at high tide, low tide
and falling tide. Examination of the timing and location of the interfacial waves are
important because they influence the nature of sediment transport in the Main Harbour
Channel.
During high river discharge periods, the sediment concentration and volume flux
estimates indicate that the river is the main source of sediments. For the low river
discharge periods, the observations suggest that the possible source of suspended
sediments observed in the lower saline layer are either from outside of the harbour or
bottom sediments being resuspended on the rising tide.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:UNB.1882/36782 |
| Date | 01 April 2012 |
| Creators | Toodesh, Reenu |
| Contributors | University of New Brunswick, Faculty of Science, Department of Geology |
| Publisher | Fredericton: University of New Brunswick |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Thesis or Dissertation |
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