Z-Boat Survey Demonstrations in Challenging Places
The first Oceanscience Z-Boat demonstrations in Canada were completed in early November 2013, concluding just as the first big snow of the year started falling. The demonstrations were arranged around highway bridges as most attendees were particularly interested in surveying close to bridges and conducting river cross sections in moderate to fast-flowing water. The demonstrations even included an underwater topographic map of a hydroelectric reservoir with a rapidly rising water level.
While in Alberta for the Tailings and Mine Waste 2013 Conference in the mountain town of Banff, optimism prevailed and three days of demonstrations were arranged in Calgary to coincide with the conference; fingers were immediately crossed in the hope that the weather would cooperate. With several survey firms in the area signed up, thoughts of conducting a typical demo on a pond were quickly frozen out and a river location was required. After the floods in the Calgary area in the summer, river access was more limited than usua. However a couple of good locations were spotted with the help of Google Maps.
Although the river was not quite as cooperative as the weather, with maximum velocities at under 1.2m/s (4 ft/sec), the attendees were nevertheless able to get their first try at conducting remote cross sections with the Z-Boat - still able to make 4m/s headway against the current! The first demo site, at the Glenmore Trail highway bridge was an example of the remote boat approach. With much of the area too shallow for a regular boat, and parts of the area too deep to wade this would represent a tricky survey proposition. The raw data shown below in the Eye4Software Hydromagic acquisition package covers about 200m upstream of the bridge, and took about 2 hrs to complete. The HYPACK hydrographic survey software was also used.
As the Z-Boat was in Calgary - home to Hemisphere GNSS - it was naturally fitted with the company's A325 GNSS receiver when surveying in non-RTK mode although a local survey company provided a Trimble R8 for a test of the Z-Boat's RTK operation. Both software packages are able to survey in "RTK Tide Mode" with the RTK GNSS antenna allowing the bathymetry results to be expressed in terms of bottom elevation and not just depth below the water surface. This survey method is particularly useful for river studies where the water surface elevation is not constant over the survey area. Indeed, during the second day's demonstrations at Cochrane, just outside Calgary, the hydroelectric dam upstream opened up and the river stage increased by over 40cm during the day. While depth results became progressively higher through the day, the RTK GNSS antenna on the Z-Boat (receiving cell phone corrections from a local network) was able to automatically eliminate this variation and generate a consistent underwater topographic map. Such datasets can be easily merged with land survey terrain models.
