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Producing a Tide Gauge Network with Geodetic Leveling Control

Authors: Matthew Widlansky, Jonathan Avery, Derek Young, Jason Klem, Nikolai Turetsky, Jerard Jardin, Linta Rose, Xue Feng, Adam Devlin, Philip Thompson, Ayesha Genz, and Greg Dusek

Abstract

To enhance monitoring and understanding of coastal sea levels, as well as provide information for adapting to sea level rise, the University of Hawaii Sea Level Center is installing new tide gauges throughout the Hawaiian Islands. All of the tide gauge stations are designed according to quality-control standards developed by the UNESCO-IOC Global Sea Level Observing System (GLOSS), along with two additional geodetic leveling steps. Firstly, to facilitate long-term monitoring of sea levels relative to the coastline, the vertical datum of each station is held constant with respect to the regional land elevation. New for this Hawaii tide gauge network, all of the water level measurements are referenced to an island-specific vertical datum, which is based on each station elevation with respect to a constant tidal datum. On the island of Oahu, for example, elevations of five new tide gauges are referenced to the tide gauge in Honolulu Harbor. We determined station elevations by surveying with respect to an existing benchmark network in Hawaii that is on a common datum (NAD PA11 ellipsoidal height). Measuring water levels with respect to island-specific datums will support adaptation planning to address sea level rise by determining how sea levels vary by location. We also recorded ellipsoidal height differences from the gravitational model for Hawaii (GEOID12B) to transfer sea levels into a physically consistent framework. Here, the methodology for implementing the Hawaii tide gauge network will be presented, along with discussion about applicability to other regions where long-term monitoring of sea levels is important.