HEC GEOHMS TUTORIAL PDF

Geospatial Hydrologic Modeling Extension HEC-GeoHMS, User’s Manual. Public Domain That information is also provided in Appendix E of this manual for. This tutorial is designed to expose you to basic functions in HEC-GeoHMS ( ArcGIS version) to create input files for hydrologic modeling with HEC-HMS. Step 7: Terrain processing and HEC-GeoHMS model development The DEM, land use and soil data used in this tutorial are already clipped.

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You have already downloaded the three required zip files cf. If not, you will find the links to the data also below. The ArcCatalog-view of the data folder is shown below:. Preparing land use data for CN Grid. Create a new empty map, and save it as cngrid. The grid is added with a unique symbology assigned to cells having identical numbers as you can see below:.

A description of some of the land classes and their associated numbers can be found here. Perform the re-classification of classes. Eventually, we are going to use these land use classes and soil group type, in conjunction with runoff curve numbers CNto create the curve number grid. Save the map document. The processing of land use data for preparing curve number grid is now done.

Preparing Soil data for CN Grid. You may get a message asking you to index fields.

You can respond to this message by selecting either yes or no – it does not matter in this exercise because we will join the table only once. With the attribute table open, right click on SoilCode field to open the field calculator and then equate SoilCode to component.

Just ignore this message and continue. Now remove the join and save the map document. Before we proceed, let us deal with rows for SoilCode field. If the number of Null rows is significantly jec, you may want to consult other resources before assigning SoilCode to these rows.

You can use select by attributes option to do this. This is critical when we have polygons with more than one soil group for eg. You can select features based on SoilCode and then use field calculator to assign numbers to tutlrial. Microsoft Excel, Open Office Calc. The preparation of soil data is done at this point. Merging of Soil and Land Use Data. You can also verify this by looking at other fields. One way to deal with sliver polygons is to assign missing values to all features.

For this exercise we will take the easy route, but you may want to populate these features for other studies depending on your project needs. Save your edits, stop the Editor, and save the grohms document. This finishes the processing of ttorial data for creating the curve number grid. The next step is to prepare a look-up table that will have curve numbers for different combinations of land uses and soil groups. The spatial tutorisl in conjunction with the look-up table can then be used to create curve number grid.

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Creating CN Look-up table. Once the table is created, create the following fields in it:. Save the edits and stop the Editor. So create a field named LandUse type: Choose the hfc parameter as Curve Number which is default in the next window, Click OK, and then select the inputs for the next window as ttuorial below:.

Help inserting CN Grid in HEC-GeoHMS | GeoNet

This process takes a while actually quite a while! Be patient and CNGrid will be added to your map document. You can change the symbology of the grid to make it look pretty! You now have a very useful dataset for use in several hydrologic models and studies. Save the map gelhms, and exit ArcMap.

Create a new empty map. Right click on the menu bar to pop up the context menu showing available tools and check the Arc Hydro Tools to add the toolbar to the map document. You should now see the Arc Hydro toolbar added to ArcMap.

Arc Hydro Terrain Preprocessing should be performed in sequential order. All of the preprocessing must be completed before Watershed Processing functions can be used. DEM reconditioning and filling sinks might not be required depending on the quality of the initial DEM. DEM reconditioning involves modifying the elevation data to be more consistent with the input vector stream network.

This implies an assumption that the stream network data are more reliable than the DEM data, so you need to use knowledge of the accuracy and reliability of the data sources when deciding whether to do DEM reconditioning.

By doing the DEM reconditioning you can increase the degree of agreement between stream networks delineated from the DEM and the input vector stream networks. Click on the Add icon to add the raster data. The added file will then be listed in the Arc Map Table of contents. The function needs as input a raw DEM and a linear feature class like the river network that both have to be present in the map document.

Set the Agree parameters as shown.

Examine the folder where you are working; you will notice that a folder named Layers has been created. This is where ArcHydro will store its grid results. This function fills the sinks in a grid. If cells with higher elevation surround a cell, the water is trapped in that cell and cannot flow. The Fill Sinks function modifies the elevation value to eliminate these problems. This default name can be overwritten. Leave the other options unchanged. Upon successful completion of the process, the Fil layer is added to the map.

Step by Step: Flood Hazard Mapping

This process takes a few minutes. This function computes the flow direction for a given grid. The values in the cells of the flow direction grid indicate the direction of the steepest descent from that cell.

The output is the Flow Direction Grid, named by default Fdr. Upon successful completion of the process, the he direction grid Fdr is added to the map. This function computes the flow accumulation grid that contains the accumulated number of cells upstream of a cell, for each cell in the input grid. Confirm that the input of the Flow Direction Grid is Fdr.

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The output is the Flow Accumulation Grid having a default name of Fac that can be overwritten. Upon successful completion of the process, the flow accumulation grid Fac is added to the map.

This process may take several minutes for a large grid! Adjust the symbology of the Flow Accumulation layer Fac to a multiplicatively increasing scale to illustrate the increase of flow accumulation as one descends into the grid flow network. Confirm that the input for the Flow Accumulation Grid is Fac. The output is the Stream Grid named Str, default name that can be overwritten.

Objective methods for the selection of the stream delineation threshold to derive the highest resolution network consistent with geomorphological river network properties have been developed and implemented in the TauDEM software http: For this exercise, choose 25 km 2 as the threshold area, and click OK. Upon successful completion of the process, the stream grid Str is added to the map. This Str grid contains a value of “1” for all the cells in the input flow accumulation grid Fac that have a value greater than the given threshold as shown in above figure.

All other cells in the Stream Grid contain no data. The cells in Str grid with a value of 1 are symbolized with black color to get a stream network as shown below:. This function creates a grid of stream segments that have a unique identification. Either a segment may be a head segment, or it may be defined as a segment between two segment junctions. All the cells in a particular segment have the same grid code that is specific to that segment. Unless you are using your sinks for inclusion in the stream network delineation, the sink watershed grid and sink link grid inputs are Null.

The output is the stream link grid, with the default name StrLnk that can be overwritten. Upon successful completion of the process, the link grid StrLnk is added to the map. At this point, notice how each link has a separate value. This function creates a grid in which each cell carries a value grid code indicating to which catchment the cell belongs. The value corresponds to the value carried by the stream segment that drains that area, defined in the stream segment link grid.

The output is the Catchment Grid layer.

Cat is its default name that can be overwritten by the user. Upon successful completion of the process, the Catchment grid Cat is added to the map. The rasters created up to now have all been stored in a folder named Layers. The vector data will be stored in a feature dataset also jec Layers within the geodatabase associated with the map document. This function converts a catchment grid into a catchment polygon feature. Confirm that the input to the CatchmentGrid is Cat.

The output is the Catchment polygon feature class, having the default name Catchment that can be overwritten.

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