Resource Concepts, Inc. has recently outfitted our kayak for highly accurate bathymetric measurements of the near shore of the Lake Tahoe lakebed. As part of our professional land surveying services, we are frequently asked by our clients to perform bathymetric surveys in conjunction with pier and buoy permits within state lands on both sides of the Nevada and California border. A bathymetric survey is the measurement of the bed of a body of water, or an underwater topographic map.
Our system consists of an on-board mounted Lowrance Elite-3X depth finder paired with our robotic Carlson CR2 total station. On the kayak, a fixed height prism pole is mounted directly over the depth finder’s transponder attached to the interior side of the bottom of the hull of the kayak behind the operator’s seat. On the shore, the total station is set up over a known survey control point.
The system requires two operators, one on shore and one in the boat. As the desired location is reached by the boat operator, he contacts the on-shore technician at the total station by two-way radio that he is ready to take an observation. The robotic total station instrument is already automatically following the prism mounted on the boat by means of internal motion control sensors. When the on-shore technician receives the word to take an observation, all he needs to do is press a button to record the observation and confirm to the boat operator by radio that the observation has been recorded. At that moment, the boat operator manually records the depth indicated on the depth finder, and the data is collected.
At the end of the day, all of the data collected in the field is downloaded to the office computer. The robotic total station sends data directly to a data collector (electronic field book), which includes the x, y and z (elevation) coordinates of each observation taken. The office technician then subtracts the depth recorded by the depth finder and the fixed height of the prism assembly to determine the elevation at the bottom of the lake.
As most of our bathymetric surveys are performed within 600 feet of the shoreline, we have not yet gotten close to the 1,645 foot depth of Lake Tahoe, nor have we seen any sign of “Tahoe Tessie”, but we’ll keep you posted.