GIS 337 Lab 3 - Delineating Watersheds
Goal and Background:
The goal of this lab was to examine and learn how to delineate watersheds in order to understand the flow of the water, and in to further prevent pollution from entering the watershed. By knowing the boundaries of a watershed, hydrologist professionals can understand how to protect and sustain the water quality in an area where water enters.
Methods:
Part 1: Data Processing
To begin the lab, data about the Adirondack Park from upper New York State was unzipped as well as data from a hydrology shapefile from Cornell University. In addition to that data, an digital elevation model (DEM North America) was used from ArcGIS online. Using analysis tools, a 20 km buffer was created around the park boundary later so that the data would be presented more clearly. The hydrology shapefile was projected to match the coordinate system of the park boundary layer, which happened to be North America NAD 1983 projection. Raster clipping was then used to clip the basemap to match up with the park boundary buffer and finally, a last projection was made to match the park boundary layer.
Part 2: Delineation of Watersheds
After buffering, clipping, and matching projections within the given layers, a watershed delineation analysis was completed. In order to do so,several new inputs were created. The inputs were flow direction, filled sinks, water accumulation, a source raster, and stream links. Using the spatial analyst tool kit, a flow direction raster was created to determine where the streams in the watershed were leading. Sinks appeared to be depressions that make water difficult to flow (although hard too see), and so the sinks were removed using the "fill" tool within the spatial analyst toolkit. Determine where water accumulates was the next step, and this was done by using the "flow accumulation" tool using the flow direction tool. A source raster was then needed for further delineation. The size of the total watershed needed to be analyzed, and thus, the threshold for the number of cells that flow into other cells was set at 50,000 using standard querying language and the "Con" tool. The last step to actually delineate that watersheds was linking all the streams using the "stream link" tool, then transforming the results to vector data. Alas, watershed delineation was possible and performed.
The watershed tool was used and another clip was performed to fit the park boundary. Lastly, the hydrology, clipped watershed, and park boundary layers were created into an image which was turned into a map (see below).
Sources:
New York State Adirondack PArk Agency. New York State GIS Clearninghouse, Adirondack Park Boundary. http://gis/ny/gov/ Cornell University Geogspation Information Repositiory. Hydrology shapefile (provided by Dr. Curtis) http://cugirmannlib.cornell.edu/index.jsp ArcGIS online, 30 second DEM.
The goal of this lab was to examine and learn how to delineate watersheds in order to understand the flow of the water, and in to further prevent pollution from entering the watershed. By knowing the boundaries of a watershed, hydrologist professionals can understand how to protect and sustain the water quality in an area where water enters.
Methods:
Part 1: Data Processing
To begin the lab, data about the Adirondack Park from upper New York State was unzipped as well as data from a hydrology shapefile from Cornell University. In addition to that data, an digital elevation model (DEM North America) was used from ArcGIS online. Using analysis tools, a 20 km buffer was created around the park boundary later so that the data would be presented more clearly. The hydrology shapefile was projected to match the coordinate system of the park boundary layer, which happened to be North America NAD 1983 projection. Raster clipping was then used to clip the basemap to match up with the park boundary buffer and finally, a last projection was made to match the park boundary layer.
Part 2: Delineation of Watersheds
After buffering, clipping, and matching projections within the given layers, a watershed delineation analysis was completed. In order to do so,several new inputs were created. The inputs were flow direction, filled sinks, water accumulation, a source raster, and stream links. Using the spatial analyst tool kit, a flow direction raster was created to determine where the streams in the watershed were leading. Sinks appeared to be depressions that make water difficult to flow (although hard too see), and so the sinks were removed using the "fill" tool within the spatial analyst toolkit. Determine where water accumulates was the next step, and this was done by using the "flow accumulation" tool using the flow direction tool. A source raster was then needed for further delineation. The size of the total watershed needed to be analyzed, and thus, the threshold for the number of cells that flow into other cells was set at 50,000 using standard querying language and the "Con" tool. The last step to actually delineate that watersheds was linking all the streams using the "stream link" tool, then transforming the results to vector data. Alas, watershed delineation was possible and performed.
The watershed tool was used and another clip was performed to fit the park boundary. Lastly, the hydrology, clipped watershed, and park boundary layers were created into an image which was turned into a map (see below).
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Map 2 - Delineated Watershed |
Sources:
New York State Adirondack PArk Agency. New York State GIS Clearninghouse, Adirondack Park Boundary. http://gis/ny/gov/ Cornell University Geogspation Information Repositiory. Hydrology shapefile (provided by Dr. Curtis) http://cugirmannlib.cornell.edu/index.jsp ArcGIS online, 30 second DEM.
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