How to use a DEM to delineate a Watershed/Basin in ArcGIS

[Music] hi everyone thanks for joining LAN geospatial tutorials in this tutorial we're going to delineate a watershed using ArcGIS hydrology tools a watershed is the upslope area that contributes flow to a common outlet as concentrated drainage it can be part of a larger watershed and can also contain smaller watersheds called sub basins to start delineating a watershed we need to download a digital elevation model of our study area we usually use the usgs earth Explorer which is a quick and easy online tool to download free Landsat imagery and other remote sensing data you after downloading and inserting de m raster in arcgis we're going to use the hydrologic modeling tools in the ArcGIS spatial analyst extension toolbox to automatically delineate the watershed we start by removing imperfections or sinks of the raster with the fill tool located in the spatial analyst tool thin hydrology open the fill tool set the input surface to the digital elevation model de M of the study area then save the output raster file then determine the direction in which water would flow out of each cell using the flow Direction tool this is the raster of the hydrologic flow direction now we are going to use the basin tool to create a raster delineating all drainage basins then we transform the result roster of basin to the vector polygon using the raster to polygon tool now we select our Basin polygon and we clip it from the shape file of all Basin polygons using the clip tool under the geoprocessing menu after that we may create the stream network so we use the flow accumulation tool to calculate the number of upslope cells flowing to a location the output flow Direction raster created in a previous step is used as the input a threshold can be specified on the raster derived from the flow accumulation tool the initial stage is defining the stream network system this task can be accomplished with the khan tool or using map algebra for example if we set the accumulation greater than 40000 all sales with more than 40,000 cells flowing into them will be part of the stream network this value depends on the size of the pixel and the raster the larger the watershed to use a higher value so this is the stream network raster we transform this stream Network raster to a polyline layer using raster to polyline tool you so here is our polyline layer of the stream network we are going to clip this stream network by watershed limits using the clip tool you you in addition to this we can clip the initial raster by watershed limits using the clip tool under the raster processing finally this is the watershed delineated using the great hydrologic modeling tools in the ArcGIS spatial analyst extension toolbox so thanks for watching this interesting tutorial don't forget to subscribe to mon geospatial youtube channel and visit our website and facebook page for more great GIS tutorials see you in the next video [Music] you

Channel: Monde Geospatial

Views: 169,072

Rating: 4.9048133 out of 5

Keywords: Digital Elevation Model, ArcGIS, Spatial Analysis, Watershed, watershed delineation using DEM, Geographic Information System

Id: 1dJvvk85n1k

Length: 12min 20sec (740 seconds)

Published: Wed Jan 04 2017

Reddit Comments

[u/[deleted]]

I know he said something like it depends on how big the raster is and how big the cells are but I am wondering if there is a better explanation for how to find the threshold value for accumulation cells that define a stream?