Failed to execute Generate CNGrid

Question

Hi!

I have encountered errors during generation of CN grid like Failed to execute (Generate CNGrid). But when I opened the attribute table of the merged land use and soil data to check if I missed something, there is an added column for CN and has value in it. Can somebody please explain what this means? Can I trust and use this result?

Thank you very much.

Sincerely,

Florence

renzsamonte · Answer

Ok thank you very much.

On Friday, 9 November 2018, 12:19:08 AM GMT+8, Kurtis Baron <geonet@esri.com> wrote:

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Re: Failed to execute Generate CNGrid

reply from Kurtis Baron in Hydro - View the full discussion

It's OK to manually encode the CN values where necessary.

I don't know what the Longest flowpath error issue is.  Could be an issue with different versions of ArcGIS, Arc Hydro, Python, or something in the registry.  You might have to digitize your own flowpaths based on contours, but then you might get hydro ID messages or other errors.  Maybe someone from Esri's Arc Hydro group will chime in...

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KurtisBaron · Answer

It's OK to manually encode the CN values where necessary.

I don't know what the Longest flowpath error issue is.  Could be an issue with different versions of ArcGIS, Arc Hydro, Python, or something in the registry.  You might have to digitize your own flowpaths based on contours, but then you might get hydro ID messages or other errors.  Maybe someone from Esri's Arc Hydro group will chime in...

renzsamonte · Answer

Mr. Kurtis,

Thank you very much Mr. Kurtis for your clear explanation. I appreciate it very much. I attached here is the result of the CN generation. In the first figure, there is no CN grid in the Table of Contents but there is value when I click the "Identify" icon on the merged polygon of soil and land use. The figure below the attachment is the attribute table of the merged polygons showing the added column for CN. Is it alright if I manually encode the CN values wherever it is necessary?

Sir, I hope you don't mind if I share with you another concern and it is about the Longest Flowpath. I always get errors even if I followed carefully the procedures. Thank you very much.

Florence

On Thursday, 8 November 2018, 12:13:52 AM GMT+8, Kurtis Baron <geonet@esri.com> wrote:

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Re: Failed to execute Generate CNGrid

reply from Kurtis Baron in Hydro - View the full discussion

Florence,

The way we’ve made curve number grids is to make a lookup table that has a column for land use and a column for hydrologic soil group (A, B, C, or D), and CN.  So, for a particular land use and a particular soil group you decide on a curve number based on the literature.  When you generate a curve number grid the software looks at the land use grid, and looks at the soil group, and finds the curve number associated with those two variables in the lookup table and assigns the value it finds to the output CN grid for all cells in the grid extent.

You could therefore use the Identify tool to click on cells in your watershed and look at the values for all layers: land use grid, soil group grid, and the output CN grid, and see if the lookup table value for that land use and soil group matches the value in the output CN grid.

I noticed there’s some videos online when I searched for how to make a curve number grid.

Kurt

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cn grid results.docx

longest flow path error.png