La Prele Reservoir, Wyoming
The La Prele Reservoir has been an important water resource for agriculture in eastern Wyoming since the dam was constructed in the 1920’s. Feeding into the North Platte River, this supported vital irrigation during the dry season for generations. This aging infrastructure is in dire need of update, but in order to design and build the appropriate dam, engineers need to understand what the potential storage capacity of the reservoir is. Elevate was requested to collect aerial LiDAR across the project area up to the 5,500 foot contour interval, classify the ground points and merge them with a bathymetric dataset collected by a hydrographic surveying firm earlier that year. A professional land surveyor, under the guidance of the Elevate operations team, staked and collected a ground control point network around the perimeter of the reservoir. An additional 100 checkpoints were used to validate the vertical accuracy of the LiDAR elevation data.
Once The LiDAR was classified and georeferenced with the ground control point network the bathymetric data was imported to merge the two elevation datasets. After close inspection it appeared the bathymetric data was not aligning with the LiDAR, but there was a consistent vertical offset from the aerial LiDAR data. Through numerous meetings and conversations, the hydrographic survey firm, who inspected their processing methodology further, found that they had projected the data in the wrong datum. If this was left unresolved, the storage calculations across the entire reservoir would have been incorrect, potentially leading to the dam being designed wrong. Once this issue was resolved the two datasets fit seamlessly together and Elevate was able to deliver a reservoir surface so engineers could understand the accurate storage capacity of the reservoir as they began designing a new dam.
The two pictures above illustrate the area mapped and colorized by point density (left) and elevation (right). The average point density for the aerial LiDAR was in the range of 50-60 points/square foot, while the points in purple represent the bathymetric point density, which was less than 1 point/square foot.