George Mason University Department of Civil, Environmental and Infrastructure Engineering. Dr. Celso Ferreira Prepared by Lora Baumgartner

Transcription

1 George Mason University Department of Civil, Environmental and Infrastructure Engineering Dr. Celso Ferreira Prepared by Lora Baumgartner Exercise Topic: Getting started with HEC GeoRAS Objective: Create a HEC-RAS model of the George Mason University watershed using the GeoRAS toolbar in ArcMap. **Refer to the HEC-GeoRAS User Manual for definitions and context of the steps and tools in this tutorial, found in the Help Menu of the GeoRAS toolbar.** Tutorial DEM obtained from GMU Campus Lidar file (provided) Versions used for this tutorial: HEC-GeoRAS 10.1, ArcMap (Student), ArcCatalog , HEC-RAS

2 Create New Project 1. Open a blank project. Add the GMU LIDAR DEM and a basemap for visual reference. Under the Customize > Toolbars menu, enable the HEC-GeoRAS toolbar. *Save the new project before moving to layer creation. 2. In the GeoRas toolbar, select All from the RAS Geometry > Create RAS Layers drop-down menu. 2

3 3. Note the auto-generated names that are assigned to each layer. *It is recommended that the user does not change the autogenerated names for this exercise. While names may be customized, this action will add additional work in later steps. 4. Click OK. 3

4 Draw Reaches and Assign Attributes 1. Zoom in on the DEM layer to a scale that allows for visual inspection of the stream beds. *A scale of 1:400 was used for the sample pictures at right. 2. Right-click on the River layer in the table of contents. Select Start Editing from the Edit Features menu. 4

5 3. Locate the Create Feature window, usually opened to the right of the screen. To open it manually, click the associated icon on the Editor toolbar. *If the window does not appear, try closing other windows in the right sidebar which may be covering the Create Feature window. 4. Select the River Layer. 5. Select the Line drawing tool. 5

6 6. Click once at the upstream end of the left (west) reach of the GMU stream system. Continue clicking once at points along the reach. *For simplicity, the reaches are started at the point downstream of Mason Pond outflow culvert (west reach) and Sandy Creek Way (east reach). 7. To move the map during drawing, click on the hand icon. Drag the map to expose the next section of the reach. 6

7 8. Re-select the River layer in the Create Feature (drawing) window. 9. Re-select the Line drawing tool in the Create Feature window. 10. Continue drawing the stream bed until reaching the junction of the east and west GMU reaches. Double click to finish the drawing. 7

8 11. Select Save Edits and Stop Editing from the Editor dropdown menu. 12. Select the River ID icon from the GeoRAS toolbar. Click on the newly-drawn reach. 13. Enter the preferred River and Reach names. 14. Click OK. 15. Repeat steps 2 through 14 to draw and name the right-hand (east) and bottom (south) reaches. *To auto-connect the ends of each reach as they are drawn, enable the Snapping toolbar from the Customize > Toolbars menu. Select the End Snapping icon. 8

9 16. Select Layer Setup from the RAS Geometry drop-down menu. 17. From the Required Surface tab, select GRID and then 18. Select the GMU LIDAR DEM from the Terrain drop-down menu. 19. Click OK. 20. Select Topology from the RAS Geometry > Stream Centerline Attributes menu. 21. Click OK. 9

10 22. Select Lengths/Stations from the RAS Geometry > Stream Centerline Attributes menu. 23. Click OK. 10

11 Draw Banks and Assign Attributes Prep: Start editing on the Banks layer. 1. Start with the left bank, from the perspective of looking in the downstream direction. Click once to start the bank line. Follow the estimated line of the bank as shown by the DEM. 2. Double-click to end the bank line as close to the end of the river reach line as possible. 11

12 3. Repeat steps 1 and 2 to draw the right bank of the same reach. 4. Repeat steps 1 through 3 to draw the banks for the west and south river reaches. Save edits and stop editing. 12

13 Create Flowpaths 1. Select Flow Path Centerlines from the RAS Geometry > Create RAS Layers menu. 2. Click Yes to assign the stream centerline. 3. Check auto-generated layer names and click OK. 4. Click OK. 5. Start editing the Flowpaths layer. 13

14 6. Click to start the left flowpath of the first river reach. Continue drawing the flowpath by following the general shape of the stream centerline (River). 7. Double-click to end the left flowpath line. 8. Repeat steps 6 and 7 to draw the flowpaths for the east and south river reaches. Save edits and stop editing. 14

15 9. Select the Assign Flowpath icon on the HEC-GeoRAS toolbar. Click on the left flowpath of one of the reaches, from the perspective of looking in the downstream direction. 10. Select Left from the Line Type drop-down menu. 11. Click OK. 12. Click on the right flowpath of the same river reach. Select Right from the Line Type drop-down menu. 13. Click OK. 15

16 Draw Cross Section Lines and Assign Attributes Prep: Start Editing on the XSCutLines layer. 1. *Working from left to right, from the perspective of looking downstream*, draw a cross section cut line which extends to across the estimated floodplain. *The cut line should intersect the Stream Centerline (River) at a 90 degree angle. 2. Continuing to work from left bank to right bank, create approximately 15 cut lines that indicate the general curves of the river reach. *Cut lines cannot overlap. Multiple clicks can be used to allow both perpendicular crossing of the river and coverage of the floodplain. *For simplicity, do not create a cut line on a bridge, culvert, or other structure along the reach. 16

17 3. Repeat steps 1 and 2 for the remaining river reaches. *Cross sections may not cross each other. See insert for detail. *A cross section may not intersect the flowpath line(s) of more than one reach. *Note special cross sections in preparation for bridge geometry. This is required for HEC-RAS. 17

18 4. Select All from the RAS Geometry > XS Cut Line Attributes menu. 5. Confirm that the auto-filled layers are correct and click OK. 6. Click OK. 18

19 7. Check a sample cross section by clicking on the Plot Cross Section icon on the Editor toolbar. Click on a cut line and observe the graph of the cross section. 19

20 Convert NLDC to Temporary N Values; Convert to Polygon Feature 1. In the File > Add Data menu, select the National Land Cover Database.tif file provided. 2. Click Add. 3. View the attribute table for the NLCD layer. Note the column shown in the picture to the right. These values represent land cover types in the grid. 4. Select Reclassify from the ArcToolbox > Spatial Analyst > Reclass menu. 20

21 5. Select the land cover.tif grid. 6. Confirm that Value is selected as the attribute to reclassify. 7. Click the folder for the Output Raster field. *Step 8 will clear any work done in the Old Value/New Value table above it. 8. Assign the folder location and file name for the new layer. 9. Click Save. *DO NOT save the new layer to the geodatabase. Recommend saving to the same folder as the original NLCD layer. 21

22 10. Select Unique. 11. Assign the Manning s N values that correspond to each NLCD value. **An integer value is required at this point. Multiply the N Values by Click OK. 13. Click Close after Reclassification is complete. 22

23 14. Select Raster to Polygon from the ArcToolbox > Conversion Tools > From Raster menu. 15. Click Environments. 16. Select the Processing Extent drop-down menu. 17. Select the original GMU DEM layer as the Extent. 18. Click OK. 23

24 19. Confirm that the new (Reclassified) layer is selected for input. 20. Confirm that the Value field is selected. 21. Click the folder for the Output Raster field. 22. Assign the folder location for the new layer. 23. Assign the file name for the new layer. 24. Click Save. *DO NOT save the new layer to the geodatabase. Recommend saving to the same folder as the original NLCD layer. 24

25 25. Click OK. 25

26 Convert to Real N Values; Assign New Coordinate System 1. Open the Attribute Table for the new Polygon NLCD-NValue layer. 2. Select Add Field from the Table Options menu. 3. Assign the name for the new field for actual N_Value. 4. Select Float type from the drop-down menu. 5. Click OK. 6. Right-click on the new field and select Field Calculator. 26

27 7. Accept the Field Calculator notice. 8. Double-click the field name for the column that currently contains the n-values* Enter /1000 to indicate division in the calculator. 10. Click OK. 11. Note the new values in the field which now correspond to real N Values. 27

28 12. Right-click the layer current polygon layer. Select Source tab and note that the Coordinate System is not equivalent to the rest of the ArcMap project. *In graphics at right, the layer properties for the Polygon-NLCD and the XSCutLines is shown for comparison. 28

29 13. Select Project from the ArcToolbox > Data Management Tools > Projections and Transformations menu. 14. Select the newest Polygon NLCD- NValue layer. 15. Click Add. 16. Note the name of the future output file. 17. Click the folder for the Output Raster field. 29

30 18. Assign the folder location for the new layer. 19. Assign the file name for the new layer. 20. Click Save. *DO NOT save the new layer to the geodatabase. Recommend saving to the same folder as the original NLCD layer. 21. Click the folder for the Output Coordinate System. 22. Select the Projected Coordinate System that matches the XSCutlines PCS (WGS 1984 UTM Zone 18N). 23. Click OK. 30

31 Extract N Values To Table 1. Select Extract N Values from the GeoRas Toolbar > RAS Geometry > Manning s menu. 2. Select the Projected Polygon NLCD-NValue layer. 3. Select the N Value field. 4. Confirm that the proper XSCutlines layer is selected and note the table name to be created. 5. Click OK. 6. Click OK when N Values are successfully extracted. 7. To view the results, open the newly-created Manning table and confirm that N Values have been assigned to multiple points per cutline. *All N Values may not be extracted on the first attempt. Re-run Steps 1 through 7 to correct. 31

32 Draw Bridge and Assign Attributes Prep: Start editing on the Bridge layer. 1. Draw a line across the bridge at Nottoway River Lane. 2. Select All from the RAS Geometry > Bridges/Culverts menu. 3. Confirm that the auto-filled layers are correct and click OK. 4. Click OK. 32

33 Draw Obstruction and Assign Attributes Prep: Start Editing on the Blocked Obstructions layer. 1. Enable the basemap layer. Comparing it to the DEM layer, select a building located within an estimated floodplain. *The Aquatic building at the intersection of Nottoway River Lane and Patriot Circle is selected in the sample at right. 2. Draw a polygon around the footprint of the building. 3. Select Positions from the RAS Geometry > Blocked Obstructions menu. 4. Confirm that the auto-filled layers are correct and click OK. 5. Click OK. 33

34 Draw Ineffective Flow Area and Assign Attributes Prep: Start Editing on the Ineffective Areas layer. 1. Draw polygon areas directly upstream of the bridge abutments. Save edits and stop editing. 2. Select Positions from the RAS Geometry > Ineffective Flow Areas menu. 3. Confirm that the auto-filled layers are correct and click OK. 4. Click OK. 34

35 Export RAS Data 1. Select Export RAS Data from the RAS Geometry menu. 2. Confirm that the file location is correct and click OK. 3. Note the process log and click OK. 35

36 Open RAS Data in HEC-RAS 1. Open HEC-RAS. Select New Project from the File menu. 2. Assign a project name. 3. Click OK. 4. Click OK. 36

37 5. Click on the icon for Edit/Enter Geometric Data on the main toolbar. 6. Select GIS Format from the File > Import Geometry Data menu. 7. Select the file that was generated in GeoRAS. 8. Click OK. 37

38 9. Confirm that the data will be read in and that the units are set to US Customary. Click Finished Import Data. The river reaches and cross section cut lines are rendered in the HEC-RAS model. 38