topic How to show flow direction? in Water Resources Questions

How to show flow direction?

RonMan — Tue, 23 Jan 2018 11:28:33 GMT

I was able to derive the catchments for each stream crossing. Now, I have two questions:

1. My question is how can i show flow direction? So that i can verify the upstream catchments generated are correct.

2. Is there a way eliminate the white gaps (between pour points and near the road alignment) between the catchments?

I have tried the vector field symbology in Flow direction raster but gives arrows not according to the streams.

I have tried the vector field symbology in the original dem raster and it gives better results but still alot of areas not in accordance with the stream generated.

I have attached a snapshot.

Thank you.

Ron

Re: How to show flow direction?

ThomasColson — Tue, 23 Jan 2018 13:52:15 GMT

Run though the Hydro Network Generation tools, that will give you a flow direction enabled flag, from which you can add arrows to the vector streams. The white "gaps" are a result of areas to the "east" of your road not falling within the same drainage area. Sounds like you need more detail than the DEM is providing. One way to do this is to "burn" the road network into the DEM by "raising" the dem a few feet where your road is, then burning through it where your culverts are. TAUDEM is much better suited for this type of catchment delineation.

Re: How to show flow direction?

RonMan — Tue, 23 Jan 2018 16:48:45 GMT

I appreciate your prompt reply Thomas. Very encouraging for an ArcGIS beginner. I think i was able to find a way. You are correct that some streams are still missing thus producing the white gap areas. I made in flow accumulation raster - symbology>graduated>clasify range from 5,000 to 100 and it produced the missing streams. For the direction arrow, i followed a video where the methodology is resample a flow direction raster then convert it raster to point then change the symbology of the point according to direction.

I will look into your recommendation of Hydro Network Generation tools. I'll try find where i can access those tools.

Thomas, i do not understand yet the burning method you mentioned as i am beginner. I'll see also what is Taudem.

Best Regards,

Ron

Re: How to show flow direction?

RonMan — Tue, 23 Jan 2018 17:59:44 GMT

I am still wondering why the vector field symbology is not giving the correct direction for the flow direction raster and original dem raster, any idea why?

Re: How to show flow direction?

ThomasColson — Tue, 23 Jan 2018 18:35:57 GMT

screen shot?

Re: How to show flow direction?

RonMan — Wed, 24 Jan 2018 05:14:54 GMT

Thomas,

This is the vector field symbology of original raster which shows incorrect.

This is the vector field symbology of Flow direction raster which shows incorrect direction also

This is the direction arrow from the resampled flow direction raster which shows correct

Thanks,

Ron

(U.A.E.)

Re: How to show flow direction?

ThomasColson — Wed, 24 Jan 2018 11:51:04 GMT

How are you symbolizing the raster? The stream network appears to be correct (dendritic). If the flow direction raster was wrong, your stream network would look like a bowl of spaghetti.

Re: How to show flow direction?

RonMan — Wed, 24 Jan 2018 12:35:15 GMT

Hi Thomas, here is a snapshot of vector field symbology. When i use this on the flow direction raster, arrows are incorrect.

Thanks,

Ron

Re: How to show flow direction?

ThomasColson — Wed, 24 Jan 2018 12:43:48 GMT

Ok you are attempting to do something with the FDR raster....that isn't supported....the FDR raster, assuming you used the D8 method (pre 10.6), results in a raster with one of 8 values for each pixel, each value an integer representation of one of (ONLY 😎 cardinal directions.

http://gisgeography.com/wp-content/uploads/2015/04/Flow-Direction-150x150.png

Convert the raster to a point feature class, and symbolize, and use rotate symbol by attribute.

Re: How to show flow direction?

RonMan — Wed, 24 Jan 2018 12:46:38 GMT

Thomas, do you mean Arc hydro for the Hydro Network Generation tools?

Re: How to show flow direction?

RonMan — Wed, 24 Jan 2018 12:49:32 GMT

Yes, that is how i did after resampling to arrive at the proper flow arrows.

So in 10.6, the FDR vector field symbology should work fine?

Re: How to show flow direction?

ThomasColson — Wed, 24 Jan 2018 13:12:28 GMT

The screen shot you provided will not correctly symbolize the FDR raster. Were you able to convert the original, unsampled FDR raster to a point feature class, and use arrow symbols rotated by attribute (you'll have to convert the integers to a real azimuth using https://community.esri.com/external-link.jspa?url=http%3A%2F%2Fgisgeography.com%2Fwp-content%2Fuploads%2F2015%2F04%2FFlo…

Re: How to show flow direction?

RonMan — Wed, 24 Jan 2018 13:22:49 GMT

Yes Thomas, i have tried that too before resampling. It gives correct result after applying the symbol rotation for each integer representation of direction. I just resampled so that i don't arrive with congested arrows.

Re: How to show flow direction?

ThomasColson — Wed, 24 Jan 2018 14:01:49 GMT

By resampling the flow direction, you are going to get different (and not one of the 8 "legal") pixel values, that have nothing to do with flow direction. Use a symbol weighting scheme that will only show one arrow per 8 pixels with the original. However, completing the Arc Hydro Hydro Network Generation will accomplish the same thing. You really can't symbolize flow direction the way you're trying to.

Re: How to show flow direction?

RonMan — Wed, 24 Jan 2018 14:13:15 GMT

Thank you for pointing that out Thomas, much appreciated. I do have another question. How can i associate the pour points with the catchment area? What i have right now are two shape files. First shape file contains the catchment polygons with additional field for the area. And the other shape file contains only the pour points.

Thanks.

Best Regards,

Ron

Re: How to show flow direction?

ThomasColson — Wed, 24 Jan 2018 14:15:51 GMT

If you run through EACH TOOL in the terrain processing and the hydro network tabs, you will get a hydro point layer, which represents the pour points, and can be related to the catchments using the hydroID field.