Drainage values indicate the direction that water will flow out of the cell, and are assigned during the process of creating a flow direction grid for the landscape. A sink is a cell that does not have an associated drainage value. The Fill tool in the Hydrology toolbox is used to remove any imperfections (sinks) in the digital elevation model. Step 2 Create a depressionless DEM Note: This step is not necessary when using OIH data from the OMNRF. Open ArcToolbox from the main menu and expand the Spatial Analysis Tools > Hydrology toolbox to view its contents. If necessary, enable the Spatial Analyst extension (Customize > Extensions > Spatial Analyst). Browse to Environment Settings > Raster Analysis and use the drop down arrow to set the Cell Size property to be the same as the DEM layer. Trent University Library Maps, Data & Government Information Centre (MaDGIC) Revised July 2015 Software: ArcGISÄ¢ 3. Further information about the file geodatabase format can be found here. It is a good idea to create an empty file geodatabase for this purpose. Under Workspace, set the variables for Current Workspace and Scratch Workspace to the directory where you wish to save your results. Use the Add Data button to add the DEM for your area of interest to the map. Open ArcMap and create a new, blank map document. Should you have any questions regarding how to access the OIH or other government data sets, please contact us for assistance at Step 1 Set up your work environment Use the steps below to set up your map document and establish the working directory you will be using throughout the watershed delineation process. Obtaining the OIH data set will allow users to skip many of the time-consuming and resource-intensive steps in the process, as noted throughout this guide. Note that the Ontario Ministry of Natural Resources and Forestry (OMNRF) have released many of the data outputs that are created in this process as a packaged product known as Ontario Integrated Hydrology (OIH) data. This guide assumes that you have obtained the required data, which includes a digital elevation model (DEM) and stream network file for your area of interest. The process outlined in this document includes steps for delineating watersheds in ESRI s ArcGIS Desktop software. Watersheds can be delineated manually using paper maps, or digitally in a GIS environment. 1 Watershed Delineation with ArcGIS 10.3.x Watersheds, also known as basins or catchments, are physically delineated by the area upstream from a specified outlet point.
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