In this tutorial, we will demonstrate how to georeference an imported HEC-RAS model to a river alignment. Here, we see a river model in HEC-RAS. It’s a simple straight line model. Notice that the cursor coordinates displayed on the bottom rightare not relative to any state plane coordinate system. In fact, this whole HEC-RAS model is less than one foot long. Switching over to GeoHECRASthe first thing, we will do is add a background base map. To do thatwe’ll right click on the Map Data Layers paneland select Add Base Map Layer from the displayed context menu. This will bring up the Add Base Map Layer dialog boxallowing us to select the base map to display. Although this is a personal preferencewe’re going to use the Hybrid Map from Microsoft BingThis is a decent map with good aerial photography and labelingbut the choice of base map is up to youClick OK to close the dialog boxNext, we’ll need to select the map coordinate system that corresponds tothe map coordinate system that the HEC-RAS model was defined with. To do thiswe're going to select the File ribbon menu and then click on the map coordinates menu itemFrom the displayed Map Coordinates backstage pagewe can browse the continents, countries, and states to select the map coordinatereference system that we want. However, an easier way to select a map coordinatereference system is to use the search function. Since our project is located in North CarolinaWe can simply type in North Carolina into the search field and thethe software will display only those coordinate systems that are in North Carolina. From the displayed listing, we can see the different map coordinatereference system that corresponds to North Carolina. The coordinate system that we want is the NAD83 North Carolina, in feet. After clicking on that coordinate system entrywe can see a preview of the coordinate system bounds in the map preview window. To select the coordinate system, click on the Apply buttonWe can see that the software has automatically cropped the Microsoft Bing Mapto the map coordinate reference system limits. the software is also weThe software has also re-projected the map to the selected coordinate system projectionThis particular project is located in Godwin North CarolinaTo find this cityright-click on the map data layers panel and select Zoom ToThis brings up a dialog boxwhere we can enter this location—Godwin, North Carolinaand click on Go. GeoHECRAS will search for that location on the Internet. Let’s double click on the first item and it will zoom us into Godwin. Our particular project is on little further EastRight here. What we want to do at this point is digitize in the river alignment for this projectaccording to where the HEC-RAS model is locatedThe first option is to go to the Watershed ribbon menu and then select FEMA Flood Data. This will bring up the FEMA Flood Data dialog boxyou can specify which FEMA flood maps options that you want to displaybut the default settings are fine. Let's click OKNow, the software automatically stream the FEMA Flood Data onto our computeroverlaying the map view. From within the FEMA flood data we can see the river alignment lineAlsowe can see that a Map Legend was downloaded for us to utilizeNow, we're ready to digitize our alignment to do soTo do soLet's start by going to the GIS Edit ribbon menuFrom here, select the Draw Polylines menu item and choose the Draw Curvilinear Polylinecommand from the drop-down menuNext, we can digitize the alignment centerline for the river by clickingalong the river like so, zooming in help significantly with this processYou can do so by using the mouse scroll wheelNow, if you make a mistake don't worryYou can right-click while digitizing and select undo last point from the displayedcontext menu or simply just hit the backspace key on the keyboard to undothe last digitize point. Once we're done digitizing the river alignment centerlineright click and select Done. Just like that the river alignment centerline is createdTo save time, we've previously digitized this riveralignment center lineNow that we've done that we can turn off the FEMA flood data as well as theMicrosoft Bing Map revealing just the river alignment centerlineNext, we're going to import the HEC-RAS model to align with this riverTo do thisGo to the input ribbon menu and choose import dataFrom the drop-down menu, select Import HEC-RAS Project to import the HEC-RAS model. From the Import dialog boxWe can select the HEC-RAS model to import. Click on import and the software will import the HEC-RAS model. Now you can see that our model is in the real world coordinatesHowever, it isn't the coordinate reference system that our previous data was inTo fix thiswe're going to return to the project site by right clicking on the alignmentcenterline layer from the Map Data Layer Panel and select Zoom To Layer ExtentsNext, click on the HEC-RAS layer in the Map Data Layers panel and drag it ontothe map view in place alongside the river alignmentNow, we can see that the HEC-RAS model is in the same coordinate space as thedigitized polyline, which represents the river alignmentNext, we want to georeference the HEC-RAS river reach to the alignment polyline. Let’s start by turning on the Base Map Layer. You'll notice the small tick mark that we placed on the line just a reminder ofwhere to start. To georeference the river reach, select River Reaches from the Input ribbon menu and the selectthe Georeference River Reaches command. This will bring up the georeferenced river reaches dialog boxFrom here, select the option Snap to Alignment Centerline. Next, we want to pick near the downstream end of the river reach. Click on the Pick buttonand the software temporarily hides the dialog box and prompts us to select thealignment reference point on the map view. We can zoom in and click on the alignment polylineYou can now see where we clicked is represented by a small red dotThe software has also highlighted the selected alignment line. Now we want to do the same thing for the upstream end of the river reach. We’ll click on the Pick button again and make our way to the other end of the modelwhere we’ll click again to create this point. Once this is done, the dialog box will reappear. Now, I should point out that it is not necessary to click on both alignment points. We could have simply selected either the downstream or upstream alignment pointand the software would have figured out what it needed to doAnyways, click on the Snap button and the software will align the HEC-RAS river reach with theselected alignment polyline. Next, click on the close button to close the dialog boxNow, looking at the model, we see that the river alignment is not quite whereit needs to be. For instance, this bridge at Interstate I-95 is representedby this grey line on our HEC-RAS model, but clearly the bridge is further downstreamwhere it is located in HEC-RAS. So we'll have to move this bridge to where it'ssupposed to be located. To do this, we'll have to slide the entire HEC-RAS modeldownstream to align the bridge with the correct location. We can check this bydouble clicking on the bridge to display the bridge editorWe see that the bridge is indeed the Interstate I-95 bridge. You can also seethe bridge structure displayed in the bridge plot. Now the next thing we needto do is return to the river reaches menuand select the Georeference River Reaches Command again. This time, we're going to select the Slide Along Alignment Centerline optionand then click on the Slide buttonWe can see on the map view this highlighted line which represents theriver reach, atop of the river alignment polyline we created earlierNow, simply click the yellow line and drag it along the alignment centerlineWe can see on this yellow line the bridge structure locationwhich is represented by these two brown dots which represent the boundingcross-sections and this green dot that represents the bridge structureWe want to slide these dots with the bridge structure on the map view. Once we've aligned the bridge, right click and select Done from the display context menuand just like thatGeoHECRAS will align the HEC-RAS river reach and bridge structure to the selected location. Click on the Close button to close the dialog boxThe bridge structure is now correctly alignedbut we still have some issuesSome of the cross-sections need to be aligned. To do this, we will turn on the FEMA Flood data layer. Also, in order to better see things on the Map View, we will click on thePreferences button for the Bing Map layer and change the transparency levelmaking the map more transparent in order to make the FEMA Base FloodElevation contour lines more observable. This will help us in aligning the cross sections relative to them. Let's start with this cross section right here. Right-click on it and choose Graphic EditThis places a bounding box around the cross-section. The cross-section needs tobe rotated to be aligned parallel with the FEMA Base Flood Elevation contour. This green diamond is the cross-section rotation anchor point which we will clickon and drag over the thalweg. Next, we will click on this yellow dot representing the rotation handle and drag to rotate thecross-section so that it lays parallel to the adjacent base flood elevation contour. Now that this cross-section correctly aligned, it's on to the next oneWe can see that this cross section should follow along this contour line hereand then bend hereTo align this cross-sectionWe will go to the Cross Sections menu and select theGeoreference Cross Sections commandFrom the display dialog box Click on the Draw button. We can then draw on the Map Viewwhere the cross-section should goIt's not necessary to draw in wherethe entire cross-section needs to go rather just draw where the alignment hasthis bend. The software with its understanding that the cross-section thalwegmust continue to match the same spot, will do the rest of the alignment work. We will draw the line parallel to the bend then right-click and select Done. And we can see that the cross section is now properly aligned, bend and allAligning all of these cross sections can be a tedious yet simple processand doing so, will properly align the HEC-RAS model with the actual mapAnd with that, your HEC-RAS model has been georeferenced.
