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Mapping Hidden Channels with Genesis Live
River channel thalwegs (the line of lowest elevation within a valley or watercourse) are often dynamic, and sometimes hidden features of large river systems. Especially low slope or impounded systems. The thalweg is a critical geomorphological feature of river and reservoir systems and affects everything from sediment transport, to fisheries habitat, to algae or invasive plant control.
Thus a good bathymetric contour map is a necessary pre-requisite for effective river and reservoir management. Here, we walk you through how to use new real time technologies (C-MAP’s Genesis Live) to produce smooth, precise, and accurate maps of hidden river thalwegs all within one trip to the site and with automated post-processing with BioBase’s EcoSound. We’ll use an annotated image gallery to take you through this process.
Prerequisites:
Lowrance HDS Gen 3 or Newer OR
Lowrance Elite Ti or Ti² OR
Simrad NSS Evo3 OR
Simrad Go
Updated Software from https://downloads.lowrance.com/ or https://www.simrad-yachting.com/help–support/Software-Upgrade/ (v 18.2 or newer)
32 gb or smaller MicroSD Card
Hypothetical client/stakeholders living on “Lake Reservoir” want to control algae in this 16-acre impounded system and possibly dredge out sediment that has presumably built up over the years. The impoundment has never been mapped and they are not quite sure even how “deep” it is. They get a permit and grant from the local water management district and hire a lake management company to map and manage their lake.
The lake management company records the 200 kHz sonar (.slg, .sl2 or .sl3) on their Lowrance while traveling around the boundary of the impoundment once or twice and then did back and forth passes in order to find the thalweg (consult this blog to learn how to record sonar). [Alternatively, you could continue concentric circles the entire way as detailed in this blog which is the preferred method in small bowl-like ponds. However, the back and forth method above is best for locating and mapping channel cross-sections.]In this example, the lake management company completed their recording, uploaded it to BioBase, and a bathymetric map output was processed automatically. In most cases, this approach is more than sufficient. But for the sake of demonstration, let’s take it a step further and simulate what can be done if the client requires even greater detail about the precise location and morphology of the thalweg.
If you have software version 18.2 or Later for Elite Ti, HDS, Simrad Evo or Go, select Genesis Live in your chart menu to create a real-time bathymetric chart for your Lowrance Chartplotter.Select “Safety Shading” under the “Chart View – Depth Palatte” menu and enter a depth you’d like to make distinct from other depths so you can clearly see the thalweg in the Genesis Live Chart. In this instance, we have a channel that ranges in depth from 7-12 ft. So we selected 7 as the depth.Genesis Live bathymetric chart is finished! Note that the waterbody boundary is not known and not part of Genesis Live mapping; so users should interpret any contours outside of their track (extrapolation) with caution. In this case, we can just ignore because our primary interest is identifying where the thalweg is, which now can clearly be seen!Although the thalweg can clearly be seen in the Genesis Live map – which uses depth processing/interpolation algorithms similar to BioBase’s EcoSound – we want to get more mapping detail within the thalweg. We can make a route to follow on our Lowrance.Draw a route directly on the touch screen.Route is finished. If you have a Motorguide Xi3 or Xi5 trolling motor with Pinpoint GPS integration into your Lowrance, you can set the autopilot to navigate the route. See this video for HDS Gen3 (the 18.2 software update has more enhanced autopilot integrations since the creation of this video). Record your sonar while traveling the route. When finished, upload to BioBase and merge with the back and forth track. This will create a smoother map and more accurate bathymetric statistics important for modeling and management.
BioBase is a cloud platform for the automated mapping of aquatic habitats (lakes, rivers, ponds, coasts). Standard algorithms process sonar datafiles (EcoSound) and high resolution satellite imagery (EcoSat). Depth and vegetation maps and data reports are rapidly created and stored in a private cloud account for analysis, and sharing. This blog highlights a range of internal and external research, frequently asked questions, feature descriptions and highlights, tips and tricks, and photo galleries.
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