This week we focused on flow and watershed analysis. While I was familiar the concepts behind these analyses (e.g. physics and geology), the process of running the appropriate procedures in ArcGIS was new. We were given a Digital Elevation Model of Kuauai, HI and lead through the process of creating a stream network. This involved: processing the raw DEM to fill any sinks, generating a Flow Direction Raster, Flow Accumulation Raster, and ultimately analyzing the output against the actual streams and watersheds as designated by the USGS.
Above is my comparison of a single watershed on Kuauai, the Lumahai River Watershed, to the USGS designated watershed boundaries and stream network. This is a large watershed on the northern portion of the island, which at its terminus is a single river emptying into the Pacific Ocean, just west of the Hanalei Bay proper. The two large maps compare the modeled Lumahai watershed and streams to the actual features, using a 200 cell threshold for the stream delineation. The modeled watershed is significantly different in appearance near the northeast coast and the modeled stream system is relatively truncated compared to the actual stream system. This is likely an affect of the threshold cell size, which could be decreased to better match the true stream network.
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