As-Built Survey of Ecological Restoration Project on Heminway Pond, Watertown, Connecticut
Franklin Surveys was engaged to perform an as-built survey to document the positions of a successful river restoration, following the removal of an ancient dam structure which impounded a portion of Steele Brook. As of the year 1847, Merritt Heminway had built a mill making spooled silk thread, and the mill dam had a spillway 82 feet in width.
The purpose of this project was dam removal and ecological restoration. Precautions were taken by the contractor to protect existing utility services. Franklin Surveys’ work on the project included re-establishment of project horizontal and vertical datums, an instrumented on-the-ground field survey, and preparation of detailed mapping. For river restorations, it is typical to prepare both planimetric (overhead) and cross section (profile of the ground surface) map views.
Establishment or re-establishment of horizontal and vertical datums is one of the greater challenges that surveyors face on a daily basis. According to the NGS Geodetic Glossary, there are actually several dozen definitions of the word “datum”. In this modern era of surveying, it is also true that there are allowed to be multiple realizations of a given datum.
For example, here in Connecticut, our researchers often come across maps that reference the North American Datum of 1983 (NAD 83). But NAD 83 has been re-realized many times over. We now have instrumentation that (if properly used) can establish coordinates to the nearest 0.01 feet. Shouldn’t you expect that your surveyor understands the difference between realizations of datums that can vary by as much as a foot, and be able to note it properly on their maps?