I'm performing a drainage analysis in XPSWMM 2D. For my check on if I'm causing impacts for proposed conditions, I am exporting 2D Maps (Water Depth) out of XPSWMM 2D as an ESRI Grid File. I have done this for both the existing and proposed conditions. I am then performing a raster calculator in ArcMap between the existing condition Grid File and the proposed condition Grid File. In the XPSWMM 2D Results Exporter for the ESRI Grid File, it gives you the option on the Cell Size of the export.

Is there a good "rule of thumb" on what cell size to specify in the 2D Results Exporter? I'm using XPSWMM 2012 version (because existing conditions was modeled in XPSWMM 2012), DTM is on a 25-ft cell size, and XPSWMM 2D Grid is 70-ft. This model is for a large overflow area.

I was thinking you export the results as a 70-ft cell size since my XPSWMM grid size is also 70-ft. I couldn't find any good guidelines on this.

Thanks in advance.