Latest Contributions by MarkBoucher

Another way to see the ditches on the DEM topography is to produce the aspect raster. This creates a raster colored by the direction the slope faces. This usually looks odd, But could show you what you want. If you have spatial analyst (SA) you could install Arc Hydro. This provide tools to process the DEM to the point where you have flow direction of the raster. With the flow direction raster you can use the Arc Hydro drop trace tool that will trace where the water would flow and this would draw lines where the ditches are. These graphics can be converted to a shape file. Of course, one of the steps is to fill sinks which would fill the ditches if the downstream end of the ditch enter a culvert which would mess up the whole idea of using Arc Hydro. Another idea is to use the fill sinks tool in SA to create a filled DEM. Then subtract the raw DEM from the filled DEM and color the zero “change” in the resulting raster as no color. Then give it a blue color ramp so that it gets darker blue as the fill goes up (water gets deeper) and make it partially transparent. Now you have water filling the ditch to use as another visual aid in tracing them. ... View more

I'm still in ArcMap, not Pro. With either version you should be able to symbolize the color ramp on the DEM to view the statistics "From Current Display Extent" (see first image). This allows you to see the subtle differences in the DEM no matter what your zoom level. The second image below is a portion of our County  DEM with this setting. The third image is a zoom in on what looks flat. The color ramp adjusts for the the data in that view revealing more detail. You should be able to study parts of your DEM to tell if burning the streams is needed, especially where you are getting the small watersheds. Of course, make sure the right rasters are being used by the delineation tool. Portion of our County  DEM Zoomed in on the red square.         ... View more

If the DEM has resolution to define the streams, you wouldn't have to burn the streams into the DEM. However, if the streams are not well defined by the DEM (the cell size is large enough to "bridge" the stream and on a color ramp of the DEM [or hillshade of the DEM] the streams are not clearly visible), you may need to burn in the streams. ... View more

Have you filled sinks?  If not, that would be the step you need to do after burning streams and before flow direction.  ... View more

Seems if you can get to adjoint catchment you’ve gotten past the full sinks step. Have you? ... View more

That is a lot of data. Sorry, I don’t know how to get around the memory issue you are facing other than breaking the DEM up into smaller pieces. Then you would have to deal with multiple runs and putting the partial results back together. 10 years! Wow. I don’t get to wrestle with Arc Hydro like I did back then. We are still waiting to get ArcPro.  ... View more

I’ve not used Pro yet. I see “tool is not valid” in the error messages. Do you have all of the required Python modules installed?  I assume ArcPy is a standard instal with ESRI products, but are there others? I’ve never had to worry about that as my Programmer Analyst sets up the installations for me. ... View more

Jan, Sorry about using the odd terminology. Yes. I is a raster manipulation so that the flow direction grid is hydrologically correct. I would not assume a flow direction raster derived from a "raw"DEM would be correct. Filling the sinks is a raster manipulation, no? Arc Hydro calls all of this "DEM manipulation" with a subset of "DEM reconditioning". So the steps with or without Arc Hydro are: Obtain a rawdem (you already have). Delineate "agreestream" line features where you want the streams to be "forced" through road crossings or where underground pipes are. You don't have to add lines where the DEM will accurately a creeks or river (unless the river is really wide and you want the flow path to follow a certain thalweg. Make sure your lines through the road embankments connect to raters outside of the embankment.  Burn the streams: The term "burn" is the actual term used be ESRI in Arc Hydro for "lowering the elevation" of the DEM where a line is. Arc Hydro does this in the background, but it is basically defining a raster where the line is (line to raster conversion resulting in 0=no line, 1=line; the DEMLine in this conversation), then multiplying that raster by a large number (default in Arc Hydro is 1000, but any large value will work) then reducing the original DEM (rawdem in Arc Hydro terms) by subtracting the DEMLine from the DEM. Fill sinks: The "hole" burned where the streams were defined by lines through embankments will be filled up no matter how deep they are. Run flow direction tool and check. Adjust agreestream line features and repeat as needed. If you define a stream next to a "natural stream" that could be defined by the raster and your stream is does not line up with the natural stream, you could end up with parallel streams and the flow direction could bet confused. I had one result in flow directions that were backwards! So, watch out for this. There is a way to correct the flow direction, but that is for another thread. I have used Model Builder to do this work since it can be repetitive on larger areas. Arc Hydro is free. If you don't have admin rights to install it, ask IT. It is worth that hassle. Arc Hydro has a lot of tools and I haven't had to use all of them. https://www.esri.com/content/dam/esrisites/en-us/media/technical-papers/archydro-overviewofterrainprocessingworkflows.pdf  One of the steps I have used is Building Walls: Make a walls line feature class and place lines where you need to build walls to "block" flows from going a certain direction: Delineate a "walls" line feature ("innerwalls" and "outerwalls" in Arc Hydro). This is the opposite of burning streams. You make a line raster from the "walls" layer(s). A key here is to "breach" those walls where the "agreestream" lines are. Take a bit of creativity in the geoprocessing procedure, but is do able. May be able to do a raster calculation making the walls raster 0 where ever the "streams" raster is 1 before you multiply the walls raster by a large number and then add it to the elevation dem.) I've had to do this at railroad tracks that were not on an embankment, but where culverts conveyed flows across the tracks. The tracks were so low that the filling and resulting flow direction easily ended up with flows going right over the tracks at the wrong place. Building a "wall" along the tracks and burning a stream where the culvert was solved this. ... View more

Jan, My guess is that there is a road or railroad embankment that crosses your expected flow path (I can see it in your first image) and that the DEM is filled up there and doesn't "know" there is a culvert/bridge to for flows to go in that direction. When you fill you fill up to the lowest point on that embankment and the fill function does its job. To get around this, add a line layer and draw a line where the culver/bridge is. The create a raster (DEMLine) using line(s) with the cell size, etc. of  the original DEM. Where the line is you should have 1 and where it is not 0. Then multiply DEMLine by some big number (say 500). Now DEMLine from your original DEM  and you make DEM2. This step "burns" a hole in the DEM where the culvert/bridge is.  Run the fill tool and flow direction tool starting with  DEM2.  The fill step will fill up the "hole" where the culvert/bridge is created but only as high as the DEM is on the low side. You get DEM3. The flow direction should be as you expect it to be   The Arc Hydro add on is made for this. I created this thread (https://community.esri.com/t5/water-resources-questions/archydro-problem-solvers/m-p/1246227#M4287) focused and sharing my journey with Arc Hydro. In Arc Hydro the above layers have some default names. I believe they are (it's been an while...) DEM = rawdem line layer = agreestream DEM3 = agreedem (this is a "hydraulically correct DEM) Good luck, Mark ... View more

C, I'll share the file Target Locations and file structure on one of mine. Maybe a picture will "paint a thousand words". My project folder is "ArcHydro" and my .mxd is named "ArcHydro", so that could confuse things. But the .gdb is named after the .mxd, not the project folder. I keep the rawdem raster out in the project folder as well as other layers no part of the Arc Hydro process. Cheers! Mark     ... View more

If you fill sinks, the areas in small catchments for individual drainage inlets (catch basins) will be filled in and you will loose the definition. However, if you don't fill sinks you could have local sinks inside the small catchments that would interfere. Have you burned pipes as streams? Burning  pipes as streams will avoid filling these local sinks. One problem with burning in the pipes as streams, though, is you do loose definition of the "interior" small catchments that are served by an individual catch basin. If there is a way to limit how much the sinks are filled, then you might be able to find a happy medium where you fill the minor sinks just enough to make the watershed delineation work for interior small catchments to catch basins. I've use Arc Hydro for larger watersheds. My process is to burn the pipes into the DEM prior to filling sinks. Then the flow direction is done. After that, other steps such as flow accumulation are used to define catchments. These processes don't define a particular watershed. You use batch points or another method to delineate those. I think there is now a more complex Arc Hydro process that allows you to define points for catch basins that remain as sinks and then you use another grid or polyline dataset that defines the subsurface pipe system. I would think this requires accurate storm drain pipe and inlet datasets. I'd love to have time to learn this, but it is more refined that I have time (or good data) for. For Arc Hydro, see possible solutions in this thread: https://community.esri.com/t5/water-resources-questions/archydro-problem-solvers/m-p/499200#M2431 ... View more

Sorry. I don’t yet use Pro. I don’t have access to my ArcMap right now and am out until 11/28. ... View more

Stream burning is simply creating a raster using a line (agreestream) giving it a big value, and subtracting it from the rawDEM. If you want to make it a more gentle drop into this “slot”, or make sure cells near the slot drain to the slot, you can make a polygon from the agreestream with a buffer and also make it a raster and give it a small value and subtract it from the first burned DEM. Walls are the opposite: You make a raster from a line with a large value and add it to the DEM. The agree steam would also need to be used as the breach line and so you would make the wall raster value zero at the intersection of the wall. Note that to block flow with a wall it needs to be at least two cells thick to stop diagonal flows. A stream can be one cell thick since you can have diagonal flow (flow out of a corner of the cell). ... View more

I have not ventured into Pro yet. Sorry. ... View more

See possible solutions in https://community.esri.com/t5/water-resources-questions/archydro-problem-solvers/m-p/499200#M2431 ... View more