Retracing the Past: Recovering 19th Century Benchmarks to Measure Shoreline Change Along the Outer Shore of Cape Cod, Massachusetts

Abstract

Between 1887 and 1888, Henry L. Marindin, Assistant Topographer of the U.S. Coast & Geodetic Survey, conducted a detailed survey of the outer shores of Cape Cod, Massachusetts, providing an important base line for future comparisons, “which will be of value to geologists and others who study the changes in the coast-line”. In 2007, the Land-Sea Interaction Program of the Provincetown Center for Coastal Studies began a project to resurvey Marindin's profiles and cross-sections to quantify changes to landforms and the nearshore environment that have occurred over the past century for use in estimating future conditions in the context of climate change and sea level rise. In order to facilitate reliable, quantitative shoreline comparisons, the translation of historical spatial data to contemporary horizontal (e.g., NAD83) and vertical (e.g., NAVD88) reference systems is paramount. With historical transects translated to NAD83 using methods developed as part of a previous study, the goal of this work is to develop an accurate estimate of the relationship between Marindin's elevation data and NAVD88. Recognizing that the physical and social landscape had changed significantly over the past 120+ years, a historical base map was prepared to assist with the recovery of 19th century benchmarks. Using the base map, five Coast survey benchmarks were recovered and resurveyed. Based on the results of this work, the local mean sea level datum of Marindin's survey is estimated to be 1.13 feet (0.34 meters) below the NAVD88 plane of reference.