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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 57 (1973)

Issue: 4. (April)

First Page: 771

Last Page: 771

Title: Synoptic Surf-Zone Sedimentation Patterns: ABSTRACT

Author(s): Benno M. Brenninkmeyer

Article Type: Meeting abstract


A new device, the almometer, has been constructed which instantaneously measures the changing elevation of the bottom and distribution of bedload and suspended load in a water column. Three almometers were placed normal to shore in the surf zone at Point Mugu, California. Data for 20 tidal cycles show that mean grain size in the mid-swash zone is coarser on the ebb than on the flood. Except when the tidal inequality is small, skewness of the sand becomes negative on the ebb and positive on the flood. There are 6 episodes of profile change which increase seaward in magnitude per tidal cycle. Erosion increases from 6% of breaker height on the beachface to 14% on the shoreface. The frequency of motion of sand in the inner and outer surf zones is virtually independent of the eep-water wave period, but the relation improves somewhat in the breaker, transition, and swash zones. Outside the breaker zone, sand moves primarily as bedload, in pulses coincident with the prevailing swell period. Inside the breaker zone, sand moves more rapidly, with frequencies equal to both seas and swell. Bottom elevation changes of more than 6 cm/wave are not uncommon. Sand seldom is thrown into suspension. In the outer surf zone, sand movement is rare, but in the inner surf zone sand suspension increases in frequency, elevation, and duration. At the still-water level, sand motion by suspension becomes dominant. In the swash zone, sand motion reverts to bedload. At Point Mugu, the amount of sand thrown into suspension 6 in. above the bottom per tidal cycle per foot of beach lengt is from 200 to 400 cu yd.

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