Wave influence on coastal sand transport paths in a tidally dominated environment

Pattiaratchi, Charitha and Collins, Michael (1988) Wave influence on coastal sand transport paths in a tidally dominated environment. Ocean and Shoreline Management, 11 (6), 449-465. (doi:10.1016/0951-8312(88)90025-2).

Abstract

Detailed physical oceanographic and sedimentological data, collected from a coastal embayment and adjoining inner continental shelf, are used to exemplify the changes in sediment transport vectors which take place when wave action is superimposed upon that of tidal currents. The area selected for study is one which is subjected to large tidal ranges (10.2 m on spring tides) and occasional storm-induced swell waves (with a predicted 50-year maximum wave height of 15 m).

Bedload transport vectors are determined, on the basis of self-recording current meter observations combined with transport formulae and fluorescent or radioactive sand tracer studies, for:

1. (i) an ‘open’ area of the inner shelf, with regular bathymetry running parallel to the coastline;

2. (ii) a ‘near-coastal’ location, where current flow is constricted by the coastline itself; and

3. (iii) in the vicinity of a linear sandbank, which rises some 10m above the surrounding sea bed.

On the basis of analyses carried out for various tidal and wave conditions, the outer (‘open’) area is considered to be one through which sedimentary material passes from the offshore deep water areas to adjacent beaches. Here, the net transport paths are susceptible to wave action and can reverse during storms, in comparison to tidal currents alone. Inshore, the sandbank is at the ‘distal’ end of the transport system: sand is concentrated onto the bank by recirculating tidal currents, but is removed from its crestline by wave action. Wave action also intensifies sand transport rates around such an effectively ‘closed’ system, enhancing the hydrodynamically controlled maintenance process.

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