Date

Spring 2025

Document Type

Master's Thesis (Open Access)

Degree Name

Master of Science (M.S.)

Department

Moss Landing Marine Laboratories

Abstract

The coastal environment is a dynamic and complex system constantly in flux. A comprehensive understanding of the nearshore system is crucial for habitat management, modeling coastal hazards, as well as managing economic resources. Studying nearshore bathymetric environments through mapping has traditionally been challenging due to high surveying costs and adverse environmental conditions. The Monterey Canyon Head offshore of Moss Landing, California exemplifies a complex nearshore feature with significant impacts on the local environment. Previous studies have identified the canyon head as the primary sand sink for two littoral cells: the Santa Cruz and Southern Monterey Bay cells. Nevertheless, the spatial and temporal trends of sediment accretion and erosion in the canyon head remain poorly understood. To address this, a cost-effective multibeam system for high-resolution mapping of complex seafloor topography in shallow water has been assembled, enabling high-frequency repeat mapping of the canyon head. Preliminary testing demonstrates that the system is capable of mapping seafloor features at 1 m resolution at depths up to 60 m, with increasingly finer resolutions achievable at shallower depths. Tests conducted at the canyon head showed repeatable mapping surveys with a 95% confidence interval of 20 cm between back-to-back surveys. The greatest differences were observed on steep (>50°) canyon walls and in deeper water (> 35 m). A total of seven test surveys were completed between October 2021 and January 2022 resulting in an average survey frequency of twice per month. Comparison maps of these surveys reveal a complex sedimentary cycle characterized by frequent sediment deposition, movement, and failure in the northern tributaries of the canyon head, and minor deposition and bedform migration in the southern tributaries.

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