Relationships between nearshore water circulation and sandy beach geomorphology at Durras, New South Wales
Date
1974
Authors
Eliot, Ian George
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Abstract
Daily field surveys of the nearshore water circulation and inshore-foreshore
morphology, along a 2.25 kilometre bay head beach at Durras on
the South Coast of New South Wales, are reported. Three main elements
of the nearshore water circulation pattern are discerned; primary and
secondary rip catchments and rip catchment divides. Associations between
nearshore water circulation and inshore-foreshore morphology are
established by pairing the primary elements of circulation with inshore
bar and foreshore characteristics. Relationships between the primary circulation and morphology
generally are in accord with the observations of McKenzie (1958a), Sonu,
et a l . 3 (1966), and Sonu (1972). Catchment divides most frequently
occur over breaker zone bars, inshore shoals, low water shoreline and
shoal edge projections. On the other hand, primary rips flow seaward
from shoreline and shoal edge embayments, through channels breaching
the breaker zone bar, and discharge beyond the breaker line.
Secondary rips are sometimes associated with promontory-embayment
morphology, in a manner similar to primary rips but at a smaller scale.
This suggests that secondary cells may influence swash intensities and
other beach face processes, as suggested for primary rips. However,
secondary rips are seen here as accessory features, developing either
as ephemeral cells within higher-energy primary catchments, or
characteristically developing under declining energy conditions.
The association between primary rips and shoreline embayments
raises interesting problems. Several cases are recognised, which
apparently form in different ways: first , by progradation of the
embayment "horns", during low to moderate wave conditions; and second,by beach back-cutting within the embayments. Back-cutting may result
from severe backwash erosion, or slope fai lu re. Since observations at
Durras show slope failure to be more widespread than previously
considered, the role of slope fai lure on sandy beaches is qualitatively
explored.
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