Lab 3: Applications in GIS

This week's lab covers watershed analysis for Kuauai, Hawaii.  The first step of the analysis was to use the fill tool to fill any errors in the DEM file.  This is down so the flow of the watershed is more accurate and removes the sinks.

The next step was to use the Flow Direction tool.  This tool determined all the different directions the water would flow.  The tools determines the 8 possible directions by analyzing one cell to the next.  The cell direction goes from one cell to the lowest.

The third step uses the Flow Accumulation tool.  This tool produces a layer that accumulated the cells and collects a cell count.  This shows the number of cells that would flow using the flow direction raster.  The flow accumulation for the cell represents the upstream cells that flow in that direction.  I then added a threshold of 200 cells.  This produced an output that contained steams with 200 cells or greater.

The next step was to use the Stream to Feature tool.  This coverts the streams to vector files and also maintains the direction of the streams.  By using the Stream Link tool, it allowed me to clearly identify individual streams.  Next it was important to determine the hierarchy and scale of the streams by using the Stream Order tool.  This also looks at the flow direction of the streams.

Once the previous steps are completed, I used the watershed tool.  The output showed the where the streams drain out to.  I then added a pour point to the map at a location where the stream drains to the ocean.  The watershed tool shows where the watershed drains to for that pour point.

The results of this analysis compares streams to streams of the National Hydrography Dataset.  I then also compared the modeled watershed to the NHD watershed.

Watershed Analysis