1989 Walker Branch Watershed Surveying and Mapping Including a Guide to Coordinate Transformation Procedures

Abstract

Walker Branch Watershed is a forested, research watershed marked throughout by a 264 ft grid that was surveyed in 1967 using the Oak Ridge National Laboratory (X-10) coordinate system. The Tennessee Valley Authority (TVA) prepared a contour map of the watershed in 1987, and an ARC/INFO{trademark} version of the TVA topographic map with the X-10 grid superimposed has since been used as the primary geographic information system (GIS) data base for the watershed. However, because of inaccuracies observed in mapped locations of some grid markers and permanent research plots, portions of the watershed were resurveyed in 1989 and an extensive investigation of the coordinates used in creating both the TVA map and ARC/INFO data base and of coordinate transformation procedures currently in use on the Oak Ridge Reservation was conducted. They determined that the positional errors resulted from the field orientation of the blazed grid rather than problems in mapmaking. In resurveying the watershed, previously surveyed control points were located or noted as missing, and 25 new control points along the perimeter roads were surveyed. In addition, 67 of 156 grid line intersections (pegs) were physically located and their positions relative to mapped landmarks were recorded. As a result, coordinates for the Walker Branch Watershed grid lines and permanent research plots were revised, and a revised map of the watershed was produced. In conjunction with this work, existing procedures for converting between the local grid systems, Tennessee state plane, and the 1927 and 1983 North American Datums were updated and compiled along with illustrative examples and relevant historical information. Alternative algorithms were developed for several coordinate conversions commonly used on the Oak Ridge Reservation.