Latest Contributions by MarkBoucher

You can do some approximation using relative water levels. This thread was posted very recently and addresses that. http://forums.arcgis.com/threads/79620-Calculate-maximum-flooded-area-based-on-maximum-flood-levels-along-a-stream ... View more

Myla-Rae, Does the watershed delineation process using Arc Hydro produce data that is then a necessary input for hydraulic modeling? Arc Hydro is used for watershed delineation for hydrology analysis and does not link to hydraulic models. A "partner" program, one that is like Arc Hydro is HEC-GeoHMS. This is also developed by ESRI for the US Army Corps of Engineers (you can find its free download on the USACOE HEC website). GeoHMS is used to perform the watershed analysis like Arc Hydro and then create field in different datasets that will be used to export HEC-HMS modeling files. The HEC-HMS can be used to actually run the hydrology analysis (calculate hydrographs). Similarly, HEC-GeoRAS (also developed by ESRI for the USACOE) uses Arc Map data to eventually export to files that can be used by HEC-RAS to perform open channel flow calculations (calculates energy and hydraulic grade lines). GeoRAS can also import RAS output back in to Arc Map for display of the results of floodplains, etc. The only data links that I can think of is a data storage system (DSS) developed by the USACOE for the HEC programs. It is the DSS format. HMS saves it output to a .dss file. RAS can read the .dss file data. This is very handy for unsteady flow analysis in RAS. The DSS format has nothing to do with ESRI products as far as I know. I am also wondering if the river schematic produced from the stream definition tool can be used to guide the digitization of the river center lines in Arc using HEC-GeoRAS. The drainage lines created using Arc Hydro will be "jagged", that is, thy are created going from raster grid center to raster grid center. They will not be smooth lines and I would not use them directly for GeoRAS. If you have a very very fine DEM, you could possibly smooth them out, but I suspect that a very fine raster would result in more sinuosity of the thalweg and still not be appropriate for RAS modeling. You should read up on the RAS modeling. You will likely find that the channel length used in RAS modeling is supposed to follow the "center of mass of flow", not necessarily the "center line" though the center line is probably very close. Cheers! Mark ... View more

In post #8 I proposed using the shift command. I was using it to shift the raster around in each direction and then use the mosaic command to find the average or max value of the cells around it. I found that focal statistics does this nicely for me. It might work for you in what you are doing (though I didn't take time just now to review your problem). I just felt the need to post my discovery of focal statistics. ... View more

In the Arc Hydro processes, I've never used Burn Stream Slope. What specifically are you using it for? Here is a link to a collection of solutions and strategies I've collected: http://forums.arcgis.com/threads/48100-ArcHydro-Problem-Solvers ... View more

Precipitation and rainfall/runoff transformation modeling is done by another program. GIS is excellent for extracting data from geographic data, but is does not do the actual hydrology calculations. ... View more

I'm pretty sure Arc Hydro will not take spill volume and do an analysis like that for you. You would have to do that another way. I assume that an oil spill would coat the flow path (stream, pipe, bowl) and there would a loss of volume along the way reducing how far the spill would travel (assuming it is not carried by water). That kind of analysis would likely have to be done outside of Arc Hydro and possibly GIS. There might be some way to measure the surface area of a creek along a path using another extension (3D analyst using a TIN?), but that would be outside my experience in GIS. ... View more

This is a job for topology and is precisely what it is made for. To use the topology you have to put the features in a geodatabase, (maybe also a dataset w/in the geodatabase). Then you create a topology. In the topology you create rules. In your case, the rule would be "Must Not Have Dangles" (polylines which have ends that don't connect.) When you check the topology, topology error "layers" are created to identify the errors. There is a topology toolbar. There are tools on it that allow efficient location and manipulation of features to fix or ignore the topology errors. For example, you can get a list of specific topology errors just in the extent of the view you are in so you can fix them. Then you can pan over and check the topology in another view. You can also check the entire dataset at once. Links: http://www.esri.com/news/arcuser/0401/topo.html http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//001t000000sp000000.htm (search for dangles for your case). ... View more

Arc Hydro tutorials for moved: http://forums.arcgis.com/threads/79329-ArcHydro-Tutorial-and-Documentation ... View more

If you are looking for a way to click on a point where a spill occurs and see a line that indicates where the spill may go downstream based on topography inside or outside of a river system, the flow direction grid produced by Arc Hydro (or tools in Spatial Analyst) will provide that. There is a flow path trace tool for that. You would need to process the DEM up to the point of the flow direction grid for that function. If you wanted to have a layer of flow paths, you could take the process further to create the steam grid or stream links (rasters) and then drainage lines (polylines). In the DEM processing, you can "burn in" the storm drain pipes so they are like trenches in the DEM. If they are burned in correctly, they can help you trace the subsurface flow path if the oil got into the storm drain system. GeoHMS has the same functions as Arc Hydro, but is focused on getting the data ready to export to a HMS hydrology model. Probably not what you want. GeoRAS is like GeoHMS in that it is used to get data ready to export to a hydraulic model. Also probably not what you want. ... View more

Is there a way to correct the corrupted spatial reference? ... View more

Make sure your snap_distance is large enough to make the pour point select a major stream in the stream grid. snap_distance = Maximum distance, in map units, to search for a cell of higher accumulated flow. From: http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//009z00000055000000.htm ... View more

I then read that you need to merge these together by using the raster calculator and adding these values together. Have you tried the Data Management Tools.tbx\Raster\Raster Dataset\Mosaic command? This doesn't add them, it has several options such as use the value of the last raster listed. This will leave your values alone. ... View more

Looks like my first step is to take my very large(geographically) DEM and clip it to just the area I want. You can also limit the area your will process using the Geoprocessing>Environments...>Processing Extents and set the processing extents to equal some feature class that just covers you project area. ... View more

Check the watershed dataset and look at the how many watersheds there are. See if you have some that are very very small, you may have put your points off the stream grid. They should be exactly on a stream grid. If they are not, they may delineate a "watershed" that is only a few cells in size. In fact, I think I can see a small "blob" near a point to the right of the green watershed in the image you posted and some others also in different places. I use Arc Hydro more than Spatial Analyst. Arc Hydro has a setting to "snap" the points to the stream grid to avoid this. ... View more