Hec Georas Arcgis 9 3 Form – Fill Out and Use This PDF

Tutorial on using HEC-GeoRAS with ArcGIS 10 and HEC-

RAS Modeling

Prepared by

Venkatesh Merwade

School of Civil Engineering, Purdue University

vmerwade@purdue.edu

June 2012

Introduction

This tutorial is designed to expose you to basic functions in HEC-GeoRAS for pre- and/or post-processing of GIS data and HEC-RAS results for flood inundation mapping using ArcGIS 10. It is expected that you are familiar with HEC-RAS and ArcGIS. If you want to get into details of HEC-GeoRAS that are not covered in this tutorial please refer to the HEC-GeoRAS users manual.

Computer Requirements

You must have a computer with windows operating system, and the following programs installed:

1.ArcGIS 10

2.HEC-GeoRAS version 5

3.HEC-RAS version 4.0

You can download HEC-RAS and HEC-GeoRAS for free from the US Army Corps of Engineers Hydrologic Engineering Center website http://www.hec.usace.army.mil/software/

Data Requirement

The only essential dataset required for HEC-GeoRAS is the terrain data (TIN or DEM). Additional datasets that may be useful are aerial photograph (s) and land use information. The dataset supplied with this tutorial includes a small portion of the fictional Baxter River available with HEC-GeoRAS users manual.

The data (11.1 MB) required for this tutorial is available at ftp://ftp.ecn.purdue.edu/vmerwade/download/data/georasdata.zip. Download the zip file on your local drive, and unzip its contents. The GeoRASData folder contains two sub- folders, one TIN dataset, and one aerial image (as raster grid) as shown below (ArcCatalog view):

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FromStation/ToStation, Assign LineType, Construct XS Cutlines, Plot Cross Section, and Assign Levee Elevation) as shown in circles and boxes, respectively in the figure below.

The RAS Geometry menu contains functions for pre-processing of GIS data for input to HEC-RAS. The RAS Mapping menu contains functions for post-processing of HEC-RAS results to produce flood inundation map. The ApUtilites menu contains functions mainly for data management. The Help menu is self-explanatory. You will learn about functions associated with these menus and buttons in the following sections.

Setting up Analysis Environment for HEC-GeoRAS

Using GIS for hydrologic/hydraulic modeling usually involves three steps: 1) pre- processing of data, 2) model execution, and 3) post-processing/visualization of results. To

create a geometry file, you need terrain (elevation) data. Click on Add button in ArcMap, and browse to baxter_tin to add the TIN to the map document. You must have the same coordinate system for all the data and data frames used for this tutorial (or any GeoRAS project). Because baxter_tin already has a projected coordinate system, it is applied to the data frame. You can check this by right-clicking on the data frame and looking at its properties. Next, click on RAS GeometryLayer Setup. Select baxter_tin as the single TIN in the Required Surface tab, and click OK.

Creating RAS Layers

The geometry file for HEC-RAS contains information on cross-sections, hydraulic structures, river banks and other physical attributes of river channels. The pre-processing using HEC-GeoRAS involves creating these attributes in GIS, and then exporting them to the HEC-RAS geometry file. In HEC-GeoRAS, each attribute is stored in a separate feature class called as RAS Layer. So before creating river attributes in GIS, let us first

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create empty GIS layers using the RAS Geometry menu on the HEC-GeoRAS toolbar. Click on RAS GeometryCreate RAS Layers. You will see a list of all the possible attributes that you can have in the HEC-RAS geometry file. If you wish, you can click on individual attribute to create a single layer at a time, or you can click on All to create all layers. For this tutorial, click on ALL to create all layers.

In the Create All Layers window, accept the default names, and click OK.

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HEC-GeoRAS creates a geodatabase in the same folder where the map document is saved, gives the name of the map document to the geodatabase (Baxter_georas.mdb, in this case), and stores all the feature classes/RAS layers in this geodatabase.

After creating RAS layers, these are added to the map document with a pre-assigned symbology. Since these layers are empty, our task is to populate some or all of these layers depending on our project needs, and then create a HEC-RAS geometry file.

Creating River Centerline

Let us first start with river centerline. The river centerline is used to establish the river reach network for HEC-RAS. The baxter_tin dataset has the Baxter River flowing from east to west with Tule Creek as a tributary. So there are three reaches: upper Baxter River, lower Baxter River and Tule Creek Tributary as shown below:

We will create/digitize one feature for each reach approximately following the center of the river, and aligned in the direction of flow. Zoom-in to the most upstream part of the upper Baxter reach to see the main channel (black outline shown in the above figure).

To create the river centerline (in River feature class), start editing. In the create features window, select River for features and Line for construction tools as shown in the figure below.

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Now open the attribute table of River featureclass, and you will see that the information you just provided on river and reach names is entered as feature attributes as shown below:

Also note that there are still some unpopulated attributes in the River feature class (FromNode, ToNode, etc.).

Before we move forward let us make sure that the reaches we just created are connected, and populate the remaining attributes of the River feature class. Click on RAS Geometry Stream Centerline Attributes All

Confirm River for Stream Centerline and baxter_tin for Terrian TIN, River3D for Stream Profiles, and click OK. This function will populate the FromNode and ToNode attribute of the River feature class. This will populate all attributes in River, and will also create

3D version (new feature class) of River centerline called River3D. Now open the attribute table for River, and understand the meaning of each attribute.

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HydroID is a unique number for a given feature in a geodatabase. The River and Reach attributes contain unique names for rivers and reaches, respectively. The FromNode and ToNode attributes define the connectivity between reaches. ArcLength is the actual length of the reach in map units, and is equal to Shape_Length. In HEC-RAS, distances are represented using station numbers measured from downstream to upstream. For example, each river has a station number of zero at the downstream end, and is equal to the length of the river at the upstream end. Since we have only one reach for Tule Creek tributary the FromSta attribute is zero and the ToSta attribute is equal to the ArcLength. Since the Baxter River has two reaches, the FromSta attribute for Upper Reach = ToSta attribute of lower reach, and the ToSta attribute for upper reach is the sum of ArcLengths for the upper and lower reach. Close the attribute table, and save the map document.

Creating River Banks

Bank lines are used to distinguish the main channel from the overbank floodplain areas. Information related to bank locations is used to assign different properties for cross-

sections. For example, compared to the main channel, overbank areas are assigned higher values of Manning’s n to account for more roughness caused by vegetation. Creating

bank lines is similar to creating the channel centerline, but there are no specific guideless with regard to line orientation and connectivity - they can be digitized either along the flow direction or against the flow direction, or may be continuous or broken.

To create the channel centerline (in Banks feature class), follow the same digitization procedure by selecting bank feature and straight segment tool. Although there are no specific guidelines for digitizing banks, to be consistent, follow these guidelines: 1) start from the upstream end; 2) looking downstream, digitize the left bank first and then the right bank. When digitizing the left bank, you do not have to stop at the intersection, you can have a single bank for the whole reach. One the right hand side, however, you cannot cross the creek so you will need two separate lines for the right bank of the Baxter River. Digitize banks for all three reaches and save the edits and the map document.

Creating Flowpaths

The flowpath layer contains three types of lines: centerline, left overbank, and right overbank. The flowpath lines are used to determine the downstream reach lengths between cross-sections in the main channel and over bank areas. If the river centerline that we created earlier lie approximately in the center of the main channel (which it does), it can be used as the flow path centerline. Click on RAS GeometryCreate RAS LayersFlow Path Centerlines

Click Yes on the message box that asks if you want to use the stream centerline to create the flow path centerline. Confirm River for Stream Centerline and Flowpaths for Flow Path Centerlines, and click OK.

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Creating Cross-sections

Cross-sections are one of the key inputs to HEC-RAS. Cross-section cutlines are used to extract the elevation data from the terrain to create a ground profile across channel flow. The intersection of cutlines with other RAS layers such as centerline and flow path lines are used to compute HEC-RAS attributes such as bank stations (locations that separate main channel from the floodplain), downstream reach lengths (distance between cross- sections) and Mannings n. Therefore, creating adequate number of cross-sections to produce a good representation of channel bed and floodplain is critical. Certain guidelines must be followed in creating cross-section cutlines: (1) they are digitized perpendicular to the direction of flow; (2) must span over the entire flood extent to be modeled; and (3) always digitized from left to right (looking downstream). Even though it is not required, but it is a good practice to maintain a consistent spacing between cross- sections. In addition, if you come across a structure (eg. bridge/culvert) along the channel, make sure you define one cross-section each on the upstream and downstream of this structure. Structures can be identified by using the aerial photograph provided with the tutorial dataset. For example, we will use one bridge location in this exercise just downstream of the junction with tributary as shown below (bridge location is shown in red):

To create cross-section cutlines (in XSCutlines feature class), start editing. Digitize cross-section cutlines using the same digitization procedure as before, but follow the guidelines outlined in the previous paragraph. While digitizing, make sure that each cross-section is wide enough to cover the floodplain. This can be done using the cross-

sections profile tool . Click on the profile tool, and then click on the cross-section to view the profile. For example, if you get a cross-section profile shown in Figure A below, then there is no need to edit the cross-section, but if you get a cross-section as shown in Figure B below, then the cross-section needs editing. (Note: This tool stops the edit session so you will have to start the edit session every time after viewing the cross- section profile).

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After digitizing the cross-sections, save the edits and stop editing. The next step is to add HEC-RAS attributes to these cutlines. We will add Reach/River name, station number along the centerline, bank stations and downstream reach lengths. Since all these attributes are based on the intersection of cross-sections with other layers, make sure each cross-section intersects with the centerline and overbank flow paths to avoid error messages.

Click on RAS Geometry XS Cut Line Attributes River/Reach Names. This tool uses the River and Reach attributes of the centerline, and copy them to the XS Cutlines. Next, click on RAS GeometryXS Cut Line AttributesStationing. This tool will assign station number (distance from each cross-section to the downstream end of the river) to each cross-section cutline. Next, click on RAS GeometryXS Cut Line Attributes Bank Stations. Confirm XSCutlines for XS Cut Lines, and Banks for Bank Lines, and click OK.

This tool assigns bank stations (distance from the starting point on the XS Cutline to the left and right bank, looking downstream) to each cross-section cutline. Finally, click on RAS GeometryXS Cut Line AttributesDownstream Reach Lengths. This tool assigns distances to the next downstream cross-section based on flow paths.

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The cross-section cutlines are 2D lines with no elevation information associated with them (Polyline). When you used the profile tool earlier to view the cross-section profile, the program used the underlying terrain to extract the elevations along the cutline. You can convert 2D cutlines into 3D by clicking RAS GeometryXS Cut Line AttributesElevation. Confirm XSCutlines for XS Cut Lines, and baxter_tin for Terrian TIN. The new 3D lines (XS Cut Lines Profiles) will be stored in the XSCutLines3D feature class. Click OK.

After this process is finished, open the attribute table of XSCutLines3D feature class and see that the shape of this feature class is now PolylineZ.

Creating Bridges and Culverts

After creating cross-sections, the next step is to define bridges, culverts and other structure along the river. Since we used aerial photograph while defining the cross- sections, our job of locating the bridge is done. To create bridges/culverts (in Bridges feature class), start editing to digitize bridges. A bridge or culvert is treated similar to a cross-section so the same criteria used for creating cross-sections must be used for bridge/culverts. Using Bridge as the edit feature and the straight segment tool on the editor toolbar, digitize bridge location just downstream of the tributary junction. While digitizing the bridge, make use of the terrain model to make sure the bridge/road centerline fall on the high ground. Save your edits and stop editing.

After digitizing bridges/culverts, you need to assign attributes such as River/Reach name and station number to these features. Click on RAS Geometry Bridge/Culverts River/Reach Names to assign river/reach names. Next click on RAS Geometry Bridge/CulvertsStationing to assign station numbers. Besides these attributes, you must enter additional information about the bridge(s) such as the name and width in its attribute table as shown below.

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Use the sketch tool to define ineffective areas. The figure below shows an example of ineffective area for the bridge downstream of the tributary junction (Note: this is a polygon feature class).

HEC-RAS does not store all information about ineffective areas. Instead only the information where the ineffective area may interfere with cross-sections/flow is stored. To extract the position and elevation at points where these ineffective areas intersect with cross-sections, click on RAS GeometryIneffective Flow AreasPosition. Leave the default feature classes for IneffectiveAreas, XS Cut Lines, and Terrain unchanged. The position of ineffective areas will be stored in a new table named IneffectivePositions. Leave current user elevations unchecked, and Click OK.

Open the attributes of the IneffectivePositions table (shown below) to understand how this information is stored.

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Blocked Obstructions window, and click OK. You will notice that a new table

(BlockedPositions) will be added to the map document, and its content are identical to IneffectivePositions table.

Assigning Manning’s n to cross-sections

The final task before exporting the GIS data to HEC-RAS geometry file is assigning Manning’s n value to individual cross-sections. In HEC-GeoRAS, this is accomplished by using a land use feature class with Manning’s n stored for different land use types.

Ideally you will store this information in the LandUse feature class added to the map document. Since we created empty feature classes at the beginning of the tutorial, we do not have this information. We will remove this empty LandUse feature class, and add LandUse shapefile (stored in LandUse folder) provided with the tutorial dataset. (Note: you can also replace the LandUse feature class in Baxter_georas.mdb with the shapefile in ArcCatalog)

The land use table must have a descriptive field identifying landuse type, which is LUCode in this case, and a field for corresponding Manning’s n values. In addition, HEC-GeoRAS requires the land use polygons to be non multi-part features (a multipart feature has multiple geometries in the same feature). The issue of non multi-part features is taken care of for the tutorial dataset.

To assign Manning’s n to cross-sections, click on RAS GeometryManning’s n

ValuesExtract n Values. Confirm LandUse for Land Use, choose N_Value for Manning Field, XSCutLines for XS Cut Lines, leave the default name Manning for XS Manning Table, and click OK. (Note: Summary Manning Table is not required if n values already exist in the LandUse table.).

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Finally, verify the tables and Click OK.

After verifying all layers and tables, click on RAS GeometryExport RASData. Confirm the location and the name of the export file (GIS2RAS in this case), and click OK. During the export, you will see a series of messages as shown below.

After the export is complete, close the window. This process will create two files: GIS2RAS.xml and GIS2RAS.RASImport.sdf. Click OK on the series of messages about computing times. You are done exporting the GIS data! The next step is to import these data into a HEC-RAS model.

Save the map document. You can either close the ArcMap session or leave it running.

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Importing Geometry data into HEC-RAS

Launch HEC-RAS by clicking on StartProgramsHECHEC-RASHEC-RAS 4.0. Save the new project by going to FileSave Project As.. and save as baxter.prj in your working folder as shown below:

Click OK.

To import the GIS data into HEC-RAS, first go to geometric data editor by clicking on EditGeometric Data… In the geometric data editor, click on FileImport Geometry

Data GIS Format. Browse to BaxterRAS.RASImport.sdf file created in GIS, and click OK. The import process will ask for your inputs to complete. In the Intro tab, confirm US Customary Units for Import data as and click Next.

Confirm the River/Reach data, make sure all import stream lines boxes are checked, and click Next.

Confirm cross-sections data, make sure all Import Data boxes are checked for cross- sections, and click OK (accept default values for matching tolerance, round places, etc).

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Save the geometry file by clicking FileSave Geometry Data. Before you proceed, it is a good practice to perform a quality check on the data to make sure no erroneous information is imported from GIS. You can use the tools in Geometric editor to perform the quality check. One of the best tools for editing cross-sections in HEC-RAS is the graphical cross-section editor. In the geometric editor, go to ToolsGraphical Cross- section Edit.

You can use the editor to move bank stations, change the distribution of Manning’s n, add/move/delete ground points, edit structure, etc. You can play around with these tools and learn more about the functions.

A cross-section in HEC-RAS can have up to 500 elevation points. Generally these many points are not required, and also when we extract cross-sections from a terrain using HEC-GeoRAS, we get a lot of redundant points. This issue can be handled by using the cross-section filter in HEC-RAS. In the Geometric data editor, click on ToolsCross Section Points Filter.

In the Cross Section Point Filter, select the Multiple Locations tab. From the River drop

down menu, select (All Rivers) option, and click on the select arrow button to select all cross-sections for all reaches. Then select the Minimize Area Change tab at the bottom, and enter 250 for the number of points to trim cross-sections down to. The minimize area change will reduce the impact of change in cross-sectional area as a result of points removal. Click Filter Points on Selected XS button.

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You will see that the deck elevation is not complete. The bridge does not even cross the river in this case! So we will edit this information.

Click on Deck/Roadway editor, and delete all information (you can select the Cells and press Delete on the key board similar to an Excel operation). We will approximate the bridge width to about 1200 ft (station 2200 to 3400), deck elevation as 84 ft (high chord) and 6ft deep (low chord) as shown below:

Click on the Copy US to DS button to copy the information from upstream to downstream, and click OK. Next, we will enter pier information. We will assume twelve

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10 ft wide piers with a spacing of 100 ft. Click on Bridge Design button , and enter the information as shown below:

Click on Make Piers, and then click Close. The bridge should now look similar to the figure shown below:

You need to know the actual bridge condition to be able to accurately enter this information, but for this tutorial we have used our intuition (and creativity!) in designing

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the bridge. After you are done editing the bridge data, close the bridge/culvert editor, save geometry data and close the geometric editor. We are done with geometric data! The next step is to enter flow data. For this tutorial we will run the model in steady state condition.

Entering Flow Data and Boundary Conditions

Flows are typically defined at the most upstream location of each river/tributary, and at junctions. There are situations where you need to define flows at additional locations, but for this tutorial we will use the typical case. Each flow that needs to be simulated is called a profile in HEC-RAS. For this exercise, we will create three hypothetical profiles.

In the main HEC-RAS window, click on EditSteady Flow Data. Enter 3 for number of profiles, and click Apply Data. Enter hypothetical flow conditions for these profiles as shown below:

The flow conditions defined in the above window are upstream conditions. To define downstream boundary, click on Reach Boundary Conditions. Then select Downstream for Baxter River Lower Reach, click on Normal Depth, and enter 0.001.

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After the inundation map is created, you must check the inundation polygon for its quality. You will have to look at the inundation map and the underlying terrain to correct errors in the flood inundation polygon. Sometimes you will realize (at the end!) that your terrain has errors, which you need to fix in the HEC-RAS geometry file. The refinement of flood inundation results to create a hydraulically correct output is not covered in this tutorial - this is an iterative process requiring several iterations between GIS and HEC- RAS. The ability to judge the quality of terrain and flood inundation polygon comes with the knowledge of the study area and experience.

Save the ArcMap document. Congratulations, you have successfully finished the HEC- GeoRAS tutorial!

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