Can The Boat Float?

This week, I have been working on determining where we can safely deploy our proposed water quality sampling system. The BlueBoat, which I mentioned in a previous blog, uses two propellers to move through the water, and our worry with the system is its suitability to handle some of the river currents in our sampling domain. To evaluate whether the boat can float--but really whether it will withstand the currents--I needed to determine a relative water velocity or current for each of our proposed sampling locations. For some of these sampling locations, USGS river gages collect flow data and/or velocity data. For others, researchers have actively sampled using acoustic doppler current profilers (ADCP) and reported their findings in the literature. For a small few, no sampling has occurred and there are no river gages, so unfortunately there are a few areas for which we have no information and will likely rely on field determinations prior to sampling.

For locations where USGS collects flow data, the m³/s data provide a volume of water moved per second, which I needed to convert to m/s, the velocity at which the water moves. By dividing the flow by the cross-sectional area of each river (area measured in m²), I generate the velocity of the water. And while this measurement isn't precise, I can add large amounts of error or wiggle room to either side to make informed judgments. However, the cross-sectional areas of each river are not readily available data. For these measurements, I manually calculated the areas by generating the map you see here, which is from a digital elevation model of the United States, published by NOAA's National Centers for Environmental Information. To generate this map, I had to extract small rectangles and stitch them together, which is why the map looks disjointed and the colors don't align, since I didn't perform any smoothing steps and did not mosaic the pieces together, as my needs were related to function rather than aesthetics. For orientation, the Mississippi River Bird Foot Delta is the second rectangle from the right with the large area of gray and the river is the light blue curved line moving through the gray swatch. The digital elevation model provides data on the depth of the rivers, which I can multiply by the cross-sectional length to generate an approximate cross-sectional area. I have really enjoyed learning how to use ArcGIS, which is the geospatial program we use to do this work, as it gives me a new skill and allows me to practice with complex problem sets that I won't publish in scientific literature before I use ArcGIS to make publication quality figures.

That's it for this week. Stay tuned next week for more fun and updates.

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