Hello I want to create a basin map to create a rainfall runoff in HMs for that i installed GEO HMS nd ARC hydro. i had given input as DEM created in ERDAS and Stream netwrk digitized in ERDAs. The Stream network that was creted using ARc hydro was not similar to the original stream netwrok i digitized. Can u pls help me how to create subbasins using my digitized stream network instead of letting Arc Hydro Making Streams automaticaly. Thanks.
The DEM will not give you the same stream network that you created by digitizing unless the topography is extremely well defined (deep and well defined valleys). You will likely have to "burn" the digitized streams into the DEM first, and then fill sinks. This is called "terrain processing". the After you have processed the terrain, then will be able to continue the process of defining your watersheds.
I use the tools in Arc Hydro to burn streams (Terrain Processing > DEM Manipulation >Reconditioning), build walls, then fill sinks (see Terrain Processing > DEM Manipulation) to create a "hydraulically correct" DEM. In the flat lands burning streams an building walls is essential for creating a hydraulically correct DEM.
i had gone through that terain processing i had carried out following step:- Reconditioning-fill sinks-flow dirction-flow accumulation-and thn lastly catchment delination and thn basin... but it didnt gave me the streams as its there in physical. and as u said for building wall its is askin catchment boundary which i thought ARc will help me in making.. as whatever boundary i would make would be rough only nd full of errors.. so how to build walls.? and in burning process stream newrk has to be in vector layer or raster layer..? as at present tht layer that i hv digitized is in vector line layer only.. Is there any other way to create subbasin and basin according to our stream layer other than Arc Hydro.?
The stream layer is a polyline layer. The "walls" are known watershed boundaries and this is the form of a polygon layer. I recall trying to use a polyline layer for the walls at one time and having it work, but I usually use a polygon layer.
What Arc Hydro does is, it takes the DEM that streams are being burned into and it reduces the elevations of the cells that intersect the streams polyline plus the buffer(s) by the amounts you set. Then the elevations of the cells the wall polygon perimeter intersects (or the wall polyline intersect) are increased by a amounts you set (use at least 2 grid cells).
The final DEM, in fact, can have very deep streams and very high walls. The goals is not to create a perfect DEM from which accurate contours can be made. What you want is an accurate flow direction grid. That then becomes the basis for your flow accumulation grid, etc. I do the fill after burning stream and building walls just to make sure the bottoms of the fill streams don't have any localized low points that will mess up the flow direction grid.
Hey Mark thanks for tht info.. i was succeful in terrain processing tool.. Now i want to export my project to HMS for tht i used tool of GEO HMS main project to start new project and defined project point and project area. Now while using "generating HMS Project" it shows me following error "System.Runtime.InteropServices.COMException (0x80004005): Error HRESULT E_FAIL has been returned from a call to a COM component. at ESRI.ArcGIS.Geoprocessing.GeoProcessorClass.GetEnvironmentValue(String environmentName) at HECGeoHMS9.GenerateProject.UpdateAHD(String rasterLocation, String vectorLocation, String ahProjName)" Can you pls help me how to overcome this error. i m using ARCGIS 9.3 and GEOHMS 4.2.(downloaded from ESRI's ftp server.) Thanks Niket.