Date

Spring 2019

Document Type

Master's Thesis (Open Access)

Degree Name

Master of Science (M.S.)

Department

Moss Landing Marine Laboratories

Abstract

High frequency topographic surveying techniques were used to assess beach dynamics (shoreline change and volume differentials) at Moss Landing Beach (MLB), adjacent to a major tributary of the Monterey Submarine Canyon. Thirty-eight surveys were completed during two time periods, 2007-2001 and 2016-2017, to address short-term (seasonal) and long-term (decadal) changes in beach dynamics and evaluate fundamental beach processes. Large variations, both erosional and accretional, in beach dynamics characterized winters at MLB while summers relatively stable, suggesting an alternative perspective to the classic observation of winter beach erosion and summer beach accretion. An independent t-test revealed no significant difference between the means of summer and winter beach dynamics given that winter erosion was balanced by subsequent winter accretion. Thus, MLB beach dynamics are not characterized by winter erosion and summer accretion, but rather by winter variability and relative summer stability. The convergence of alongshore sediment transport, facilitated by wave refraction near the head of the submarine canyon, likely supplied sediment to MLB and enabled winter accretion. This sea-saw pattern of erosion and accretion during the winter may also be explained by the tendency of beaches to evolve towards an equilibrium state. A facet of this phenomenon was observed at MLB in which an eroded beach tended to subsequently accrete and vice versa. Additionally, a strong correlation (R2=0.773) suggests that shoreline change may be used as a proxy for volume differentials at MLB, a useful finding as volume differentials are often much more difficult and expensive to measure than shoreline change. The decadal difference between the survey time periods allowed for long-term evaluations of beach dynamics in which the MLB shoreline position was found to have accreted seaward at a rate of 1 m/y from 2007 to 2017. Local submarine canyon dynamics is likely a major driver of both inter- and intra-seasonal beach dynamics at MLB. However, more empirical work is necessary to verify the connection between canyon head processes and beach dynamics.

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