Modelling seabed shear stress, sediment mobility, and sediment transport in the Bay of Fundy

Abstract

Information about seabed stability and sediment dynamics is part of the fundamental geoscience knowledge required for the extraction of tidal energy in the Bay of Fundy and for the integrated management of the Bay. Waves, tidal currents, and wind-driven and circulation currents were obtained from oceanographic models to assess the wave and current processes for the broader Bay of Fundy. The wave and current outputs were coupled with observed grain size in a sediment transport model to predict, for the first time, the seabed shear stresses, sediment mobility, and sediment transport patterns for the entire Bay. The root mean square tidal current, highest in the upper Bay (>1.4 m·s −1 ), is reduced to moderate in the central Bay (0.5-0.8 m·s −1 ) and decreases further in the outer Bay (0.2-0.5 m·s −1 ). The maximum tidal current occurs in the Minas Passage and is >5 m·s −1 . The mean significant wave height, in contrast, is the greatest in the outer Bay (ϳ1.3 m) and gradually decreases to the northeast in the central and upper Bay (<0.5 m). Seabed shear in the Bay of Fundy is mostly due to tides, and wave effects are only important in coastal areas. The strongest mean shear velocity of 10 cm·s −1 occurs in the Minas Passage area. Strong shear velocity of 4-5 cm·s −1 also occurs in Minas Basin, in the central Bay, and in the narrows around Grand Manan Island. Sediment mobilization in the Bay of Fundy is predominantly by tidal current. Mobilization frequency is >30% of the time over most of the Bay and reaches 100% of the time in some areas. The maximum total-load sediment transport rate under spring tide can reach ϳ5 kg·m −1 ·s −1 and is to the northeast during flood and to the southwest during ebb. Net sediment transport flux, however, is dominantly to the northeast and reaches 2 kg·m −1 ·s −1 . Eddies of net transport are found to occur around headlands and at the narrows of Grand Manan Island, largely due to the occurrence of eddies of residual tidal flows. The regional distribution of substrate types and bedform fields and patterns of seabed erosion and deposition are well correlated with tidal current strength and sediment transport patterns.Résumé : Des données concernant la stabilité du plancher océanique et la dynamique des sédiments constituent une partie fondamentale des connaissances géologiques requises pour l'extraction de l'énergie marémotrice dans la baie de Fundy et pour une gestion intégrée de la baie. Les vagues, les courants de marée, les courants poussés par les vents et les courants de circulation ont été obtenus de modèles océanographiques afin d'évaluer les processus des vagues et des courants pour l'ensemble de la baie de Fundy. Les données de sortie sur les vagues et les courants ont été jumelées aux granulométries observées dans un modèle de transport de sédiments afin de prédire, pour la première fois, les contraintes de cisaillement sur le plancher océanique, la mobilité des sédiments et les patrons de transport pour toute la baie. Le courant de marée moyen quadratique, plus éle...

Coastal retreat rates and sediment input to the Minas Basin, Nova Scotia

“…Models (Li et al 2015;Wu et al 2011;Wu et al 2016) and observations (Amos and Long 1980) indicate that sediment transport through the Minas Channel represents a net source of sediment to the Minas Basin. Previously constructed sediment budgets, however (Amos and Joice 1977;Amos and Long 1980;Shaw et al 2012) made this impossible, because cliff erosion delivered more sediment to the Minas Basin than was stored in subtidal and intertidal deposits.…”

“…The seabed in the Minas Basin is covered by sands and gravels that are mobilized frequently by strong tidal currents (Amos 1978;Li et al 2015). Amos (1978) argued that these conditions placed the seabed in a state of hydrodynamic equilibrium, in which the sediment size on the seabed is the defined by hydrodynamic stress.…”

“…This imbalance suggests that the system should approach hydrodynamic equilibrium, due to the need for significant export of sediment from the Minas Basin out to the (Amos and Long 1980) and models (Li et al 2015;Wu et al 2011;Wu et al 2016) indicate that sediment is imported to, rather than exported from, the Minas Basin.…”

Seabed disturbance and sediment mobility due to tidal current and waves on the continental shelves of Canada

“…In Canada, limited efforts have been made to quantify the magnitude and frequency of seabed disturbance, and to use this to understand sediment transport patterns and the distribution and mobility of bedforms for some shelf regions (e.g. Li et al 2012;Shaw et al 2014;Li et al 2015).…”

“…The combined action of waves and tides, however, produces mean shear velocity up to 5 cm•s −1 , affects 93% of the bank, and mobilizes sediments to water depths as deep as 200 m. Classification of seabed disturbance types based on the relative time percentage of threshold exceedance by various processes shows that wave-dominant and mixed wave-tide disturbance types are predominant and occur respectively over >50% and 30% area of SIB. Li et al (2015) used modelled waves, tidal currents, and wind-driven and circulation currents to predict seabed shear stresses, sediment mobility and sediment transport patterns in the broader Bay of Fundy (BoF; Fig. 1).…”