LAB 3
Lab 3
GIS 2
2/25/2018
Jeffrey Hessburg
The goal of the lab is to create map illustrating a drainage basin. A drainage basin, otherwise known as a watershed, is an area where all water from surrounding surfaces converge. These are areas are determined by analyzing the topography of an area then determining the lowest points and where water will flow. The watershed is bordered from surrounding watersheds by ridges and high points that separate flow. It is important to understand and visualize watersheds to understand where water is coming from. This Lab has us determine where the watershed boundaries in Adirondack Park by following three steps: data processing, followed by data processing. then finally watershed delineation.
Collecting the data consisted of logging on to gis.ny.gov and downloading a file called Andirondak Park Boundary. The file needs to be unzipped in the correct folder, then added to ArcCatalog.
The first thing that needs to be added to ArcMap is the park boundary. Using the buffer tool, a 20 km buffer is added to the park boundary so that when the watersheds are being calculated, more topography is consider. This improves accuracy of the watersheds.
A major concern was getting all of the data to be in the same projection. If the data is not all in the same projection the results will not be very accurate. To do this a transformation is needed when adding the data. Or the project raster tool is used to change the projection the raster data is in.
Next was adjusting the DEM output cell size. The original lab calls for 60m cell size, and question three asks for 120m cell size. The smaller the cell size, the more precise the data should be, because more points would be used in making calculations. I ran into a problem when using the 120m cell size. I ran through all of the steps twice and could not get any visible results. I would assume that there would be less watershed, because the data is more generalized.
The last steps were to delineate the watersheds. To do this, first use the flow direction tool to calculate flow direction. next is to use the fill tool to fill in sinks and raise elevations to equal neighboring cells so that water can still be calculated to flow. Once this is done, a recalculation of flow direction must be done. Next eh accumulation of flow needs to be calculated using the flow accumulation tool.
A source raster must be created to be used as in input for watershed delineation. A threshold on the number of cells needs to be used. To do this the Con tool is used. The number of cells determines the size and number or watershed. for the lab a value of 50,000, 100,000, and 500,000 are used. The watersheds that used a larger number had a smaller number of watersheds in the results. You can see the results in the maps below.
The map on the left uses 100,000 cell threshold. The map on the right uses 500,000 cell threshold.
Next is to use the stream link to connect stream sections between intersections. Then finally use the watershed tool to delineate the watersheds. The watersheds are all calculated, so all that needs to be done is clip the watersheds to the map, choose a correct color scheme, and make the map look good. The map is displayed below.
The last objective was to compare the streams calculated to the actual streams. The map is below.
GIS 2
2/25/2018
Jeffrey Hessburg
The goal of the lab is to create map illustrating a drainage basin. A drainage basin, otherwise known as a watershed, is an area where all water from surrounding surfaces converge. These are areas are determined by analyzing the topography of an area then determining the lowest points and where water will flow. The watershed is bordered from surrounding watersheds by ridges and high points that separate flow. It is important to understand and visualize watersheds to understand where water is coming from. This Lab has us determine where the watershed boundaries in Adirondack Park by following three steps: data processing, followed by data processing. then finally watershed delineation.
Collecting the data consisted of logging on to gis.ny.gov and downloading a file called Andirondak Park Boundary. The file needs to be unzipped in the correct folder, then added to ArcCatalog.
The first thing that needs to be added to ArcMap is the park boundary. Using the buffer tool, a 20 km buffer is added to the park boundary so that when the watersheds are being calculated, more topography is consider. This improves accuracy of the watersheds.
A major concern was getting all of the data to be in the same projection. If the data is not all in the same projection the results will not be very accurate. To do this a transformation is needed when adding the data. Or the project raster tool is used to change the projection the raster data is in.
Next was adjusting the DEM output cell size. The original lab calls for 60m cell size, and question three asks for 120m cell size. The smaller the cell size, the more precise the data should be, because more points would be used in making calculations. I ran into a problem when using the 120m cell size. I ran through all of the steps twice and could not get any visible results. I would assume that there would be less watershed, because the data is more generalized.
The last steps were to delineate the watersheds. To do this, first use the flow direction tool to calculate flow direction. next is to use the fill tool to fill in sinks and raise elevations to equal neighboring cells so that water can still be calculated to flow. Once this is done, a recalculation of flow direction must be done. Next eh accumulation of flow needs to be calculated using the flow accumulation tool.
A source raster must be created to be used as in input for watershed delineation. A threshold on the number of cells needs to be used. To do this the Con tool is used. The number of cells determines the size and number or watershed. for the lab a value of 50,000, 100,000, and 500,000 are used. The watersheds that used a larger number had a smaller number of watersheds in the results. You can see the results in the maps below.
The map on the left uses 100,000 cell threshold. The map on the right uses 500,000 cell threshold.
Next is to use the stream link to connect stream sections between intersections. Then finally use the watershed tool to delineate the watersheds. The watersheds are all calculated, so all that needs to be done is clip the watersheds to the map, choose a correct color scheme, and make the map look good. The map is displayed below.
The last objective was to compare the streams calculated to the actual streams. The map is below.
The vector streams are the streams generated by the stream to feature tool. It can be noted how they line up well to the actual streams.
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