Interpolating Coastal Shallows via Trends in Terrestrial and Marine Topography

Abstract

Acquiring bathymetry data of coastal shallows in Puget Sound is both an important and difficult task. Puget Sound estuaries contain a large number of processes that dynamically impact coastal topography and communities, however modeling the influences of these processes is difficult without bathymetry data. For this project, the processes of sediment deposition and wave action are explored by developing profiles of two common Puget Sound environments; river deltas and bluff-backed beaches. Single-beam transects of Mukilteo and Duckabush (Hood Canal) coastal estuaries were collected in January and February of 2018 using a Garmin 441s fishfinder with a 77/200 kHz variable transducer. These transects were then decomposed into bathymetric profiles perpendicular to the coastline, aligned to supplementing GMRT land topography and marine bathymetry available in the GeoMapApp visualization tool. GMRT data was used for assessing 4 different mathematical methods to interpolate the shallows; a linear interpolation, a cubic spline, a non-modified pchip, and a non-linear logistic regression. The results from this project suggest that the most effective model between terrestrial elevation and marine bathymetry datasets is a simple pchip method, which most effectively preserves not only profile area relative to the observed data, but also demonstrates similar curvature.