Latest Contributions by MarkBoucher

This is a silly question. Sometimes the default color ramp goes from black to white. Maybe it's there but can't see it because it has no color. Have you tried changing the symbology of your new layer? ... View more

First thing I would check would be the processing extent. If it does not cover your work area, results will get cut off. Set them at : Geoprocessing>Environments>Processing Extent>Choose a dataset that covers your project area. ... View more

Sorry. Yes, "get out of Arc Hydro" =  "Close ArcGis". You don't have to create the folders and geodatabases. Arc Hydro will create them. It will also set up other things automatically and this avoids errors. After a while I succumbed to the Arc Hydro default names to save time. ... View more

Uli, I sounds like the suggested solutions aren't working. The "Attempted to read or write protected memory" error could mean that you are trying to re-run a process and ArcHydro can't overwrite a certain data file. Have you deleted everything that is created by the ArcHydro process and started fresh?  I do this often when I can't determine why the ArcHydro "hits a wall". Get out of Arc Hydro Go to the project folders and delete anything the ArcHydro created (geodatabase, raster folder, etc.) - don't delete your agreestream, rawdem, inner/outerwalls, batch points (I export batch points to a shape so I don't have to recreate them: have done that a few times  😕  ) Delete the temp files. Does this get you past the problem? Mark ... View more

Uli, I think what Dan Patterson means is that you could reduce the number of stream segments. This can be done be increasing the number of cells used to define the streams (part of the stream definition tool). I think the assumption is that this will reduce the processing memory needs and maybe you will get past the error. Best, Mark ... View more

Uli, If I were to run into the error you are describing, I would first reboot my PC. If your .mxd is on a network server, I would also move the .mxd and project to a folder with a short simple name onto the local drive (PC or laptop). The move to the local drive reduces errors that might be due to data transfers over the network. The short names (without spaces) reduces errors too, maybe related to some older codes that were made for shorter name strings (couldn't tell you for sure). On the local drive the processing also becomes much faster. If you haven't check out ArcHydro Problem Solvers​, you may find several tips like the ones above to be helpful. I started that thread and others have contributed their questions and answers. You can contribute there too if you find a solution to your problem. You just have to post a link to this thread. Good luck! Mark ... View more

My practice is to create a tool box and put several models in it. I start the names of the models with numbers so I can keep the order straight. The models may have a dozen steps or just a couple. This is how I've kept one crash from a big model from requiring a whole new start. I also will sometimes if errors are persistent, I close the mxd and delete all the output (gdbs and all). I keep any of the main inputs. Then I reboot. This is sometimes the only thing that gets me past an error. Never know why this is, but it works. ... View more

I'm currently being successful using the 10.2 version with only a few problems recently that are solved by an close/open cycle of ArcMap. My use is focused on watershed delineation and a few other tools including HEC-GeoHMS tools that are not currently part of Arc Hydro. I have never used the Level DEM tool. I'm not on 10.3 yet, but movement to there is inevitable. I can't commiserate with you on that yet. I assume you've seen the Arc Hydro Problem Solvers thread and are familiar with some tricks of the trade posted there that keep the "head beating on the wall" to a minimum. ArcHydro Problem Solvers ... View more

I have not used the flow direction with sinks tool. I look forward to seeing a solution to your problem. Mark ... View more

Grace, I haven't used HEC-GeoHMS for a while, but I'm very familiar with Arc Hydro. GeoHMS uses the same logic and tools as Arc Hydro for processing the watersheds. What GeoHMS does is take the processed grid and vector data and then allows the creation of an HMS model from that data.* Normally, when using HEC-GeoHMS (and Arc Hydro), you start with a digital elevation model (DEM) and then process it through a few steps to create a flow direction from which you derive the rivers (drainage lines). I have started the practice of not digitizing or using existing river/stream polylines until I need them for correcting the DEM where the areas is flat or the DEM is not defined enough to put river/stream in the right place. In these cases I use the agreestream polyline layer to put the river/stream in the right place and then burn them in.  See this related discussion for more on my approach to burning in streams: Stream Definition threshold value​. It looks like there is also some discussion about burning in streams in this thread. Wow! It started in 2011!! Mark *Footnote: The first generation GeoHMS tools relied on Arc Hydro tools to process the DEM before using the GeoHMS tools. Now, it appears the GeoHMS toolbar has the Arc Hydro tools needed to get to GeoHMS datasets that can be then used to build the HMS model. Likely, you would only need the GeoHMS toolbar if your goal was to create an HMS model from the GIS data. ... View more

This is a problem in flat areas. One solution is to draw a polyline in the agreestream layer and then burn the streams in. This is my preferred solution. You only need to draw polylines where you need to "train" the DEM to be lower in elevation and make it follow the creek, stream, or river. Where the GIS drainage lines follow the river there is no need to burn in a stream. When you burn the stream into the DEM you basically lower the cells in the DEM that intersect the agreestream polyline. These can be burned very deep (1000 feet or meters) because one of the next steps is to fill the sinks. When you run the fill sinks tool, the local low cells in the DEM area filled up and the elevation of the cells that were burned low will be raise up to match the elevation of the lowest cell next to them. If the lowest cell is a cell in the DEM that has a "correct" stream elevation, then the burned cells will not be raise higher than that and you will then have a corrected DEM. This can be done at bridge and culverts where you have road crossings. When a DEM is corrected using stream burning and wall building, so that the flow direction is right, you have what is called a "hydrologically correct DEM" Another solution would be to build walls. I would not normally do this to correct a stream alignment problem. A "wall" could be drawn across the incorrect stream and force the flows to not flow there. This could be a solution for some cases and is commonly used in flat watersheds to stop water from "spilling" over low ridges or known flow barriers in the watershed. For example, I often draw a polyline along railroad tracks in an innerwalls layer. Then I put an agreestream polyline where the culverts go under the tracks. Burning the streams using the agreestream layer and then building walls using the agreestream layer for the breach layer, one can do a good job of training the DEM and working towards a hydrologically correct DEM. Another solution similar to the first solution is to use an existing stream/river layer and use it to burn in all the streams. I used to do this with our countywide creek layer. Then I found that many of the polylines in the creek layer were incorrect!. I will use it as a guide and occasional copy from it to my agreestream layer, but in general I do not trust it. Hope this helps. Mark ... View more

Georgios, I found the area you are working in using Google Maps (see attached image). The area where you have the strange lines is in the water (Gulf of Corinth). If the elevation in your DEM is level in the water area, the flow direction would be somewhat random. Since you are dealing with a coastal area, you will have some unique issues to deal with. However, I don't see anything wrong with the results. There was some recent discussion on coastal drainages. Here is the link to that includes that discussion: Re: Catchment vs watershed.​ You are right that the flow accumulation is based on the flow direction. If the flow direction is wrong (has errors) the rest of the analysis will have errors. Since you have creeks, rivers, and streams that have to cross under roads on their way to the sea, I suspect you will want to create an agreestream layer and "burn" the streams into the rawdem at the road crossings so the flow direction will be correct at those locations. It looks like the topography is steep enough that for the most part you won't need to burn in streams anywhere else except in very flat place or where man-made drainage systems control the flow direction instead of the topography. So, basically you are not doing anything wrong to get the "horizontal flow lines". A possible way to get rid of them would be to use the Con() function to make every raster grid below a certain elevation (i.e. in the water) "Null". I'd have to do a bit or research myself to give you direction on how to do that. I'm sure there is a tool in Spatial Analyst that would do work. This link might show you how. ArcGIS Desktop Help 9.3 - Setting values to NoData: SetNull.​ Once the raster has null (or "no data") values in the water area, it is possible that the flow direction grid will not be defined there and so you won't get flow accumulation there either. The flow direction grid is only a foundational layer and will not show in your final analysis where I assume you will define watersheds. You might simply move on and establish your analysis process for a small area until you settle on a process you are happy with. Then perform that process on the whole dataset.  I use Model Builder in this way. I allows me to build and edit the process and they reapply it on different datasets. Best, Mark ... View more

Esther, STREAMS For watershed delineation, I would separate out the lake and pond outlines to another layer. You don't want the water outlines to act like streams. I would draw a stream through the lakes/ponds that will "burn" a stream through the dams of reservoirs. IF you need a data point a the dam, Arc Hydro can get you one later with a batchpoint on the stream at the dam. Sometimes the lakes have no data or Null in the water area. if so, I would use the CON() function to give them a value. I would then run the Arc Hydro process to burn streams and fill sinks. This will not fill the ponds that have agreestream polygons through them. Ponds that are important to the flow path related calculations that do not have streams burned through them should be checked to see if the flow direction through them makes sense. If the flow path through them needs to be corrected, you can draw an agreestream polyline through them. This polyline does not need to connect to other agreestream polylines downstream. The fill sinks process will simply bring the dem cells up to and elevation that will work. DEM ERRORS I've heard of the gridded pattern issue and experienced it one time when I had to expand the DEM I have with a neighboring county's larger sized grid DEM. I don't recall that it caused any problems. I've seen threads relating to the issue, but haven't had much experience with it, so I'm not sure I can give you solid advice. I searched and found these threads using the search words:  DEM "grid pattern". (/search.jspa?q=DEM+%22grid+pattern%22 ) Unable to produce usable contours & hillshade from GeoBase 1:50K dem Artifacts when changing to UTM Strange lines on my hillshade You might be able to find others. Best, Mark ... View more

Esther, I don't work on the coast, at least not one as complicated as yours. I'm not sure of the best approach for "grouping" the coastal watersheds especially since you have several small ones. 1.     Automated Point setting The only "automation" I know of is the general Arc Hydro process. After that you have to set points. There are readymade Arc Hydro Model Builder Terrain Preprocessing Workflows that make performing and repeating Arc Hydro tasks easier. 2.&3.   Capturing the small coastal watersheds:  It is true that on the coast you could have one grid cell watersheds. One idea that comes to mind is to do this: Add elevations to your DEM in the area of the water. This could be flat or if you have bathymetry data that would work.  You will likely have to use the Con() function or some other way to mosaic a separate constant elevation raster with your original rawdem. Add to your agreestream layer polylines that connect the mouths of the small streams/creeks to and artificial point off the coast but in the extended DEM. You these could be straight (I've attached a screen capture with freehand lines. It seems to me that event if you didn't capture all of the "mouths", this would still work). When you burn the streams in and perform the flow direction step, I suspect the flow direction of the DEM grid cells on the coast will head toward the edge and be "caught" in the burned stream. Run the Arc Hydro process. I suspect you will end up with catchments that include all of the coast line. You will then need to trim them at the original coast. Best, Mark ... View more