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UBC Theses and Dissertations

Beach profiles and sediment activity Mattila, Mark Ronald


A study of beach profiles and sediment activity has been undertaken investigating natural beaches of inner coastal southwest British Columbia and published data on laboratory beaches. Two separate types of sediment activity are focused upon: longshore sediment, activity occurring on inner coast beaches and on- offshore sediment activity occurring on wave Hume constrained laboratory beaches. Field investigative work on twenty-five natural beaches has included review of past-field studies, profile surveys, sediment tracing experiments, investigation of surface and subsurface sediment, size distribution and structure, measurement of slopes and elevations of shoreline features, review of available wave climate data and wave hindcasting for the period of profile surveys. The work has shown that inner coastal beaches are predominantly shingle beaches or cobble armoured beaches with longshore sediment transport, occurring in a narrow upper foreshore zone under wave action at high tides. There is also evidence that coarse materials (gravels and cobbles) move selectively in an onshore direction and fine materials (silts and sands) move in an offshore direction. The sediment transport processes and beach characteristics identified are different from the summer/ winter beach process known to occur on open coasts. Laboratory beaches have been studied to identify the general response of a beach profile to waves. One problem in the study of beaches has been the lack of a readily measured variable to interrelate wave action and sediment movement. By studying laboratory beach profiles a variable representing on-offshore sediment, movement has been abstracted as an area swept out by differencing two profiles as a function of time. The variable has been investigated using laboratory beach data and correlation between it and wave parameters such as height, and period is evident. A dimensional analysis of on-offshore sediment transport is performed using the swept, area variable.

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