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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Interactive Point Delineation An alternative to delineate watersheds when you do not want to use the batch mode process a group of points simultaneously to generate the watershed for a single point of interest is the Point Delineation tool. Meteorologic Model We do not have any meteorologic data temperaturerainfall etc at this point. Leave the default values in the Blocked Obstructions window, and click OK.
The output is the Catchment polygon feature class, having the default name Catchment that can be overwritten. Perform the re-classification of classes. You can use the tools in Geometric editor to perform the quality check.
Step by Step: Flood Hazard Mapping
Longest Flow Path Method computes the centroid as the center of the longest flow path within the sub basin. Delineating Watersheds for existing points eg.
You will see that two folders: The CN Lag Method function computes basin lag in hours weighted time of concentration or time from the center of mass of excess rainfall hyetograph to the peak of runoff hydrograph using the NRCS National Engineering Handbook curve number method.
Stream Link Grid file name: If cells with higher elevation surround a cell, the water is trapped geohks that cell and cannot flow.
The preparation of soil data is done at this point. Confirm the input River name, and click OK. For example, when you click on a Reach Ryou will see that Muskingum routing method geohjs associated with it.
The grid is added with a unique symbology assigned to cells having identical numbers as you can see below:. If you want to split the sub-basin at the point displayed in the tutlrial, you can use the subbasin divide tool, and click at the point displayed on the map. All vector and tabular data are stored in CedarCreek. Close the attribute table, save edits and stop editing.
Ideally you will store this information in the LandUse feature class added to the map.
Help inserting CN Grid in HEC-GeoHMS | GeoNet
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 floodplaindownstream reach lengths distance between crosssections and Mannings number. The cells in Str tutorizl with a value of 1 are symbolized with black color to get a stream network as shown below:.
In the layer setup for post-processing, first select the New Analysis option, and name the new analysis as Steady Flow. To perform a batch watershed delineation: This tells ArcHydro that the batch processing is done. Browse to your uttorial folder for Output Directory.
Certain guidelines must be followed in creating cross-section cutlines: Once the table is created, create the following fields in it: Close the dockable window, tutoral save the map document.
Click OK on the message regarding successful creation of the project. When snapping is turned on, if your point is sufficiently near to a drainage line within around 5 grid cells then the point will be snapped i. If you want to associate the watershed points with attributes from your point features, you will need to use join and relates or other ways geojms linking these attributes to watershedpoints.
Next, we will enter pier information. This tool will assign station number distance from each cross-section to the downstream end of tutorrial river to each cross-section cutline. On the other hand, watersheds may overlap For example, the two watersheds in the Watershed feature class yutorial with each other. Tuotrial the Agree parameters as shown. You have already downloaded the three required zip files cf.
Merging of Soil and Land Use Data. If not, you will find the links to the data also below. Click on the outlet grid cell at the watershed outlet as shown below:. 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. If you expand the CedarCreek basin in watershed explorer, you will see the list of junctions, reaches and subbasins.
This function allows preparing subbasin and river features for export. Sign up or log in Sign up using Google.
After the computations are complete, you can open the attribute table for subbasin, and see that a field named BasinCN is populated with average curve number for each sub-basin. Now remove the join and save the map document. 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:. We will approximate the bridge width to about ft station todeck elevation as 84 ft high chord and 6ft deep low chord as shown below:.
Upon successful completion of the process, the Catchment grid Cat is added to the map. Flow Direction Grid file name: This function converts the input Stream Link grid into a Drainage Line feature class.
You can open the attribute table of subbasin feature class to see that the subbasin methods are added to LossMet, TransMet, and BaseMet fields, respectively. In the next window, provide the following inputs: Digitize banks for all three reaches and save the edits and the map document. For now accept the default original stream definition option.