Latest Contributions by MarkBoucher

Kathy, Sorry. By "train" I meant that after I create the raster from contours and then create the contours at smaller intervals, I see if the newly created contours make sense. If not, then I add intermediate contours and repeat the process. This adding of additional intermediate contours is what I call "training". If you look a the document I linked, you will see some maps with circled areas that I felt I needed to add more intermediate contours to "train" the raster to output more reasonable contours. Hope this makes sense... Mark ... View more

If you can create a raster from your contours, you can create contours at any interval from that raster. What I did was create supplemental contours by manually interpolating halfway between the starting contours to train the raster to create contours that I agreed with. So there was still some subjectivity involved. - Mark ... View more

Kathy, I did something similar for rainfall contours using ArcMap and Spatial Analyst. I documented it here. https://www.contracosta.ca.gov/DocumentCenter/View/3914/Mean-Seasonal-Precipitation-Raster-From-Dwg-B-166-PDF?bidId= It was a while ago, but after looking at the document, I now recall I made a raster from the manually created (digitized) contours, from the raster generated finer contours, checked the accuracy of those finer (smaller interval) contours. Then I manually interpolated between the initial manual contours where needed by creating lines between the initial contours and then drawing new contours by clicking the midpoints of those lines. Tedious, but it worked. Possibly what you need is somewhere in that process. ArcPro may have a simpler tool. Mark ... View more

As I was learning the Arc Hydro process, I used to burn in all the streams using a streams layer. Then I discovered the DEM I had was 10'x10'. I realized that the majority of the stream can be identified during the Arc Hydro process. I then limited my streams to be burned to problem areas where the terrain (DEM) didn't correctly reflect the real flow path (bridges, fuzzy/confusing DEM spots).  The resolution of your DEM dictates a lot. What I see in you image above  (lower right quadrant) appears to be a very detail DEM. Is that the resolution of your DEM or another image with hillshade? ... View more

I saw this tool while looking for something else. I have not used it, but the description seems to fit your need. Mark https://desktop.arcgis.com/en/arcmap/latest/tools/spatial-analyst-toolbox/flow-distance.htm ... View more

Sam, My guess is that you have a river crossing or dam downstream that you need to burn a breach through. If this is the case, add a feature in the agreestream layer (default layer name in ArcHydro) that goes through the crossing/dam to lower the DEM in a slot through the crossing/dam so that when you fill the DEM you will not fill up the area behind the crossing. This will result in a flow direction grid that reflects the terrain. Through a lake where you don't have a bathymetry surface in the DEM, you have to add an agreestream feature that will burn through that to get a definite flow path. If you don't have Arc Hydro, you can do some Spatial Analyst to burn in some streams and fix the issue. Attached is a document I wrote and just updated to add the "Burning Steams" section. I wrote this to preserve for myself and pass on to others how I figured out how do do this process without Arc Hydro. Arc Hydro has some very handy tools and is worth learning if you are doing this repeatedly. The part about burning stream is what you would want to use to possibly address your issue. The document has not been reviewed by others so forgive any bad grammar or spelling. Hope this helps, Mark   ... View more

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