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Pathfinder Dam, Wyoming

REASON FOR PHOTOGRAMMETRY: To document the foundation conditions and geologic features during construction.  Images provided better quality data than traditional methods of geologic mapping at Pathfinder Dam, Wyoming.

PEOPLE INVOLVED: Bryan K. Simpson, P.G., P.E., 303-445-3094

PAPER ABSTRACT: This paper provides an illustration of recent photogrammetry methods used in support of geologic mapping for the design of a new spillway at Pathfinder Dam, located in the central portion of Wyoming.

Terrestrial-based photogrammetry was successfully used in conjunction with field geologic mapping.  The collections methods included collection of topographic data, and measurement of both joint and shear orientations in order to develop a comprehensive three-dimensional (3-D) model for analysis and foundation documentation and acceptance purposes.  The photogrammetric work performed consisted of rapid data collection using an off-the-shelf digital camera.  Collection of field digital photographs was accomplished by the use of a camera mounted atop a 12-foot-long survey staff and a wireless shutter trigger system.  The new spillway foundation was approximately 750 feet in length, and 20 feet in width.  The geology of the foundation consisted primarily of granitic bedrock that is cut by several prominent generally continuous joint sets, local joint sets, and shear zones.

The software available to construct 3-D models using ordinary digital images is being developed and improving at a rapid rate.  Processing methods used Adam Technologies 3DM Mine Mapping Suite software to construct this project’s photogrammetric model. Processing was performed in a reasonable timeframe, constructing approximately 150 Digital Terrain Models (DTM) pairs, and included statistical analysis of joint sets and presentation of stereoscopic pole plots. 

Lessons learned regarding the processing challenges of specific field conditions, including scaling and lighting variations, will be discussed. 

Pathfinder analysis

Contact Bryan Simpson, 303-445-3094, for more information on photogrammetry at Reclamation.