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 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. The bridge does not even cross the river in this case! Towards the end of the section 6. This function converts the input Stream Link grid into a Drainage Line feature class. Preparing Soil data for CN Grid. You can click on ttutorial reach and see its associated methods.
We will skip parameters associated with computing rainfall as these numbers should come from detailed analysis of the watershed. After creating cross-sections, the next step is to define bridges, culverts and other structure along the river.
Creating a river centerline Let us first start with river centerline. Accept the default 20 map units for Rasterization Cell Size. We are modifying the editing environment because when we digitize geoums Tule tributary we want its downstream end coincide with the downstream end of the upper Baxter Reach.
The output is the Catchment polygon feature class, having the default name Catchment that can be overwritten. You can check this by right-clicking on the data frame and looking at its properties. Adjoint Catchment Polygons file name: You should see that a single point feature class has been created comprising the outlet point where you clicked. 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 HECRAS.
After you respond to that message a project file report will be displayed as shown below: Batch Watershed Delineation This function delineates the watershed upstream of each point in an input Batch Point feature class. The output is Drainage Point with the default name DrainagePoint that can be overwritten.
Snapping of all the reaches at the junction is necessary for connectivity and creating HEC-RAS junction so make sure the three reaches are snapped correctly. While digitizing, make sure that each cross-section is wide enough to cover the floodplain.
Step by Step: Flood Hazard Mapping
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: If the number of Null rows is significantly high, you may want to consult other resources before assigning SoilCode to these rows.
Set the Agree parameters as shown. Again make sure you snap the starting point with tuyorial common end points of Upper Baxter Reach and Tule Tributary. The vector data will be stored in a feature dataset also named Layers within the geodatabase associated with the map document.
The River Lenght tool computes the length of river segments and stores them in RiverLen field.
Step by Step: Flood Hazard Mapping | UN-SPIDER Knowledge Portal
Confirm the input Subbasin and River files, and click OK. 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.
These quantities are automatically computed when a feature class becomes part of a geodatabase. Upon successful completion of the process, the polygon feature class Catchment is added to the map.
The flowpath layer contains three types of lines: A point feature class showing centroid for each sub-basin is added to the map document.
If the river centerline that we created earlier lie approximately in the center of the main channel which it doesit can be used as the flow path centerline.
These feature classes are added to the same geodatabase cedar. To tutoial the river centerline in River feature classstart editing, and choose Create New Feature as the Task, and River as the Target as shown below: DEM reconditioning involves modifying the elevation data to be more consistent with the input vector stream network.
Confirm that the input to the CatchmentGrid is Cat. The Basin Slope tool computes average slope for sub-basins using the slope grid and sub-basin polygons. You will see the reach will get selected, invoking geomhs following window:.
This will populate the remaining attributes. This tool assigns distances to the next downstream cross-section based on flow paths.