Hydrology in ArcGIS Pro, Lab Exercise 6: Creating a Flow Accumulation Raster

This lab will demonstrate the Flow Accumulation tool in ArcGIS Pro. A Flow Accumulation raster is used to calculate the size of the catchment area that drains into every point on the landscape, and is generated from the Flow Direction raster, which was in turn generated from the filled DEM. If the flow direction raster is not generated from a filled DEM, then you’ll have the same problems with your Flow Accumulation raster that you saw with your Watershed raster in Lab Exercise 2.
While these Flow Accumulation values are interesting enough in themselves, we can also use them to generate additional interesting and useful data, such as stream flow networks and a topographic wetness index. Each Flow Accumulation raster cell value will tell you the number of raster cells that drained into that cell. A value of 0 means that no cells drain into it (i.e. it is at the top of a ridge or hill). Cells that are at the exact bottom of a drainage, directly in the flow path, tend to have very high flow accumulation values, orders of magnitude larger than their neighbors, and we take advantage of these extreme differences in flow accumulation values to identify where the actual flow path is.
Basic Hydrologic Analysis in ArcGIS Pro Lecture: • Basic Hydrologic Analy...
Lab Exercises:
Lab 1: Calculating Areas from Raster Datasets; • Hydrology in ArcGIS Pr...
Lab 2: Problems when creating Watersheds without filling the DEM; • Hydrology in ArcGIS Pr...
Lab 3: Filling Sinks in a DEM; • Hydrology in ArcGIS Pr...
Lab 4: Calculating an Accurate Flow Direction Raster; • Hydrology in ArcGIS Pr...
Lab 5: Generating an Accurate Watershed; • Hydrology in ArcGIS Pr...
Lab 6: Creating a Flow Accumulation Raster; • Hydrology in ArcGIS Pr...
Lab 7: Generating a Stream Network using Strahler Stream Orders; • Hydrology in ArcGIS Pr...
Lab 8: Aspect Statistics within Watershed; • Hydrology in ArcGIS Pr...
Lab 9: Slope Statistics within Watershed; • Hydrology in ArcGIS Pr...
Lab 10: The Topographic Wetness Index (TWI); • Hydrology in ArcGIS Pr...
Lab 11: Finding the Shortest Path Through the Stream Network; • Hydrology in ArcGIS Pr...
Extra Materials:
Word Document with walk-throughs of lab exercises: docs.google.co...
Data for Lab Exercises: drive.google.c...
Manuscripts discussing TWI: drive.google.c...

[@cronoser]

Thank you very much for your explanations, thanks to your videos it's easy to understand these tools, greetings from Spain!

[@JennessEnterprises]

Thank you so much, and my apologies for taking so long to respond! I am glad the videos are useful for you, and thank you for taking the time to let me know.

[@gumballunbyg8667]

thank you so much :)

[@JennessEnterprises]

I'm glad I could help! Thank you for letting me know.

[@steaviswinson7895]

How do you then convert this to Polylines, while preserving the original values?

[@JennessEnterprises]

Hi Steavi,
That's a good question. It's difficult since every cell has a different flow accumulation value. I can think of two possibilities, both assuming you've already created your polylines (see Lab 7; ua-cam.com/video/LPGMt3y5fQQ/v-deo.html):
1) Do you really need every flow accumulation value along the stream segment recorded? If you only need the maximum value along the segment, then you can use the "Zonal Statistics as Table" tool to generate a table of Flow Accumulation statistics for each segment, then join that table to you your stream segments feature class. Then you'd have maximum, minimum, etc. flow accumulation for every segment.
2) If you do need a separate segment for each unique flow accumulation value, the you could convert your Flow Accumulation raster to a polygon feature class (which will likely produce a very large feature class), then intersect your stream segments with those polygons. This will clip every segment to the flow accumulation cell boundaries and attach that flow accumulation value to the clipped segment.
Hope this helps Steavi! Take care -
Jeff

[@steaviswinson7895]

@@JennessEnterprises Thank you so much! I watched Lab 7, it gave me exactly what I needed. I also tried the Raster to Polygon as an alternative and it also was exactly what I was looking for, and the intersect worked out perfectly for me. thank you so much!

[@JennessEnterprises]

@@steaviswinson7895 Cool, and thanks for letting me know! I'm glad I could help.
Take care -
Jeff