Quantifying wave breaking shape and suspended sediment in the surf zone

Abstract Burley Beach (southeastern Lake Huron) exhibits a multi-barred shoreface, the long-term equilibrium morphology characteristic of many low angle, sandy beaches in the Canadian Great Lakes. During a single major storm, a new bar emerged 50-60 m offshore as an irregular trough-crest form, through differential erosion of an existing shore terrace. Emergence, bar growth and offshore migration were associated with: (a) an overall negative sediment balance in the inner surf zone initially (‑2.30 m3>/m beach width), but with a large positive sediment balance (+5.10 m3/m) subsequent to the storm peak and during the storm decay; (b) progradation of the beach step to produce a new shore terrace; and (c) offshore migration of the two outer bars to provide the accommodation space necessary for the new bar. The primary transport mechanisms accounting for emergence of the new bar, its growth and migration were: (a) the mean cross-shore currents (undertow), which always transported suspended sediment offshore; and (b) the onshore transport of suspended sediment by incident gravity wave frequencies early in the storm and subsequently by infragravity waves (at the storm peak and the decay period). The longshore transport of sediment was significant in terms of the gross transport, although the net result was only a small transport to the south-west (historic littoral transport direction). It did not cause bar initiation, but it may have supplied some of the sediment for bar growth. The primary mechanism for bar initiation and growth was the cross-shore displacement of sediment by wave-driven (oscillatory) transport and cross-shore mean currents (undertow).

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LABORATORY EXPERIMENTS ON THE INFLUENCE OF WIND ON NEARSHORE WAVE BREAKING

Coastal Engineering Proceedings ◽

10.9753/icce.v21.46 ◽

1988 ◽

Vol 1 (21) ◽

pp. 46

Author(s):

Scott L. Douglass ◽

J. Richard Weggel

Keyword(s):

Wind Direction ◽

Wave Breaking ◽

Laboratory Experiments ◽

Surf Zone ◽

Breaking Waves ◽

Wave Tank ◽

Zone Width

The influence of wind on nearshore breaking waves was investigated in a laboratory wave tank. Breaker location, geometry, and type depended upon the wind acting on the wave as it broke. Onshore winds tended to cause waves to break earlier, in deeper water, and to spill: offshore winds tended to cause waves to break later, in shallower water, and to plunge. A change in wind direction from offshore to onshore increased the surf zone width by up to 100%. Wind's effect was greatest for waves which were near the transition between breaker types in the absence of wind. For onshore winds, it was observed that microscale breaking can initiate spilling breaking by providing a perturbation on the crest of the underlying wave as it shoals.

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SURF ZONE MEASUREMENTS OF SUSPENDED SEDIMENT

Coastal Engineering Proceedings ◽

10.9753/icce.v16.104 ◽

1978 ◽

Vol 1 (16) ◽

pp. 104 ◽

Cited By ~ 3

Author(s):

Timothy W. Kana

Keyword(s):

South Carolina ◽

Suspended Sediment ◽

Surf Zone ◽

Sediment Concentration ◽

Breaking Waves ◽

Bulk Water ◽

Scatter Plots ◽

Water Volumes ◽

Spilling Breakers

Suspended sediment concentration was measured in approximately 250 breaking waves on undeveloped beaches near Price Inlet, South Carolina, U.S.A., using portable in situ bulk water samplers. As many as 10 instantaneous 2-liter water volumes were obtained in each wave for a total of 1500 samples. Concentrations of suspended sediment were determined at fixed intervals of 10, 30, 60 and 100 cm above the bed for various surf zone positions relative to the breakpoint. The majority of waves sampled during 22 days in June and July, 1977 were relatively long crested, smooth, spilling to plunging in form, with breaker heights ranging from 20 to 150 cm. Surf zone process variables measured included breaker height and depth, breaker type, wave period, surface longshore current velocity, wind velocity and direction. Scatter plots of mean concentration against various process parameters indicate the amount of sediment entrained in breaking waves is primarily a function of elevation above the bed, breaker type, breaker height and distance from the breakpoint. Concentration ranged over 3 orders of magnitude up to 10 gm/1, but varied less than 1 order for samples collected under similar conditions with regard to elevation and breaker type. Plunging breakers generally entrain 1 order more sediment than spilling breakers equal in height. Despite considerable scatter, these data indicate concentration decreases with increasing wave height for waves 50 to 150 cm high, suggesting that small waves can be important in the transport of sand on gently-sloping open coasts.

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