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modelling of watershed using WMS
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Read a digital elevation model, compute flow directions, and delineate a watershed and sub-basins using outlet points.
Introduction – Images Introduction – Basic Feature Objects Editing Elevations – DEM Basics
Data Drainage Map
30-60 minutes
1 Introduction ......................................................................................................................... 2 2 Objectives ............................................................................................................................. 2 3 Setting up a Project with the Hydrologic Modeling Wizard ........................................... 2 3.1 Starting the Hydrologic Modeling Wizard ................................................................... 2 3.2 Project Filename ........................................................................................................... 3 3.3 Define Project Bounds ................................................................................................. 3 3.4 Watershed Data using Web Services ............................................................................ 4 3.5 Watershed Data by Reading Files ................................................................................ 6 3.6 Trimming the DEM ...................................................................................................... 6 3.7 DEM Fill Command ..................................................................................................... 7 4 Watershed Delineation using the Hydrologic Modeling Wizard .................................... 8 4.1 Compute Flow Directions and Accumulations ............................................................. 8 4.2 Choose Outlet Locations .............................................................................................. 9 4.3 Create Sub-basins ....................................................................................................... 10 4.4 Save the WMS Project File ........................................................................................ 12 5 Delineation Display Options ............................................................................................. 12 5.1 Display Flow Paths .................................................................................................... 12 5.2 Basin Labels ............................................................................................................... 13 5.3 Display Options .......................................................................................................... 13 5.4 Color Fill Basins ........................................................................................................ 13 6 Conclusion.......................................................................................................................... 13
Watershed delineation from DEMs is straightforward and relatively simple, provided the project area is not entirely flat or completely dominated by man-made structures. The DEM method does not work if there is no relief in the DEM elevations. This exercise teaches DEM delineation using the hydrologic modeling wizard, a step-by-step delineation approach that makes the process even simpler.
In this exercise, the basics of DEM delineation are explained using the hydrologic modeling wizard. This includes the following:
Datum to “NAD83” Planar Units to “METERS”
Zone to “12 (114°W - 108°W – Northern Hemisphere)”
Figure 2 Project Bounds in Virtual Earth
3.4 Watershed Data using Web Services
This section requires a working internet connection. Proceed directly to section 3.5 if a working internet connection is not available.
Figure 3 Use web services option
Figure 4 Download Data (Web Services) dialog
WMS will proceed to download the requested data for the project area that was specified.
7. In the main window, click on the drop-down arrow next to the Add GIS Data located in the tool bar and select Get Online Maps…
Once the image files have been downloaded from Web Services, WMS automatically opens the files into the WMS project.
Figure 5 DEM Trim Area for Web Services Data
Figure 6 DEM Trim Area
The DEM Fill command is useful for filling gaps in DEM data. It interpolates missing (no data) values using inverse distance weighting of the neighboring eight cells. This functionality is useful when tiling multiple DEMs files together in WMS, particularly if a thinning factor is applied when the DEMs are read. It is not necessary to use this command on seamless DEMs obtained from the NED. If seamless NED data was
obtained by successfully completing section 3.4 (Watershed Data using Web Services), then skip this section.
WMS computes flow directions and flow accumulations to create streams on the DEM using a program called TOPAZ.
Delineate Watershed
Figure 9 Zoom Area
Figure 10 Node Location
Figure 11 Zoom Area
Figure 12 Create an outlet at the indicated location (below the stream junction)
When finished using the elevation data, turn off the DEM contours and extra streams displays if desired.
WMS also allows each basin to be filled with a different color. This is useful when the background image does not need to be showing.
This concludes the “Watershed Modeling – DEM Delineation” tutorial. Feel free to work through any of this tutorial using copies of other data. Once completed, save a project file for future reference. This exercise explained how to use DEM data in WMS. Topics included the following:
