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Glendo Dam, Wyoming

REASON FOR PHOTOGRAMMETRY:  Discontinuity mapping for spillway modifications to document the foundation conditions and geologic features during construction.  Images provided better quality data than traditional methods of geologic mapping at Glendo Dam

PEOPLE INVOLVED: Bryan K. Simpson, P.G., P.E., 303-445-3094
This presentation provides an illustration of recent photogrammetry methods used in support of geologic mapping for design of a new auxiliary spillway at Glendo Dam, located in south central Wyoming.

Collection Methods:

Terrestrial-based photogrammetry was used successfully in conjunction with field geologic mapping, which included collection of topographic data, and measurement of joint and shear orientations in order to develop a comprehensive three dimensional model for analysis and foundation acceptance purposes. This work was performed using an off-the shelf camera with rapid data collection and reasonable processing times. A man-lift with the ability to raise personnel 50 feet into the air was used for the collection of digital photographs. The new spillway foundation excavation was approximately 550 feet in length, 50 feet in width and had unretained 0.5 horizontal to 1 vertical slope cuts 27 feet in depth. The geology of the foundation excavation consisted primarily of a siltstone bedrock that is cut by several prominent, generally continuous joint sets, bedding planes and shear zones.

Processing Methods:
The software available to construct 3-D models using ordinary digital images is being developed and improved at a rapid rate. This model was constructed using approximately 200 Digital Terrain Models (DTM) pairs. Processing also included statistical analysis of joint sets and presentation of stereonet pole plots. Lessons learned regarding the processing challenges of specific field conditions, including scaling and lighting variations, will be discussed. Photogrammetric mapping is not only applicable to existing dams, but of great importance for new construction to assure the details of the geology, concrete structures and embankments are quickly and accurately documented for current and future use. With photogrammetric models, it can be very practical to obtain remarkably accurate data, and these methods have many advantages over traditional surveys.

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