I am using ArcGIS 10.6.1 to delineate the drainage network from SRTM 30 meter DEM. I had used ArcHydro tool for the same. I found there is a discontinuation in drainage network while using UTM projection but continue drainage has been generated in GCS projection on same DEM data.
Projection transformation can shift the raster but how it can change the pixel value? Please do let me know whether it is a bug of 10.6.1 as I didn't faces such problems in 9.x version.
It sounds like your DEM could have been projected using nearest neighbor resampling, which is what you don't want with continuous data like a DEM. See the section titled, "Reprojecting the Right Way: Reprojecting Rasters with ArcToolbox" in this article for more information: https://www.esri.com/about/newsroom/arcuser/looking-good/
Thankyou for your reply, I have reproject the dem using both (Bilinear and Cubic) resampling method but still I am getting discontinuous river network.
See the above image where Red line showing the river extracted from GCS dem where there are no discontinuous network while in river extracted from reprojected dem using bilinear and cubic method, there are so many river were discontinued.
Process of "projecting" (really resampling) DEM can introduce "sinks" into the elevation model. That would explain the discontinuities you are seeing. Make sure you fill sinks in the projected DEM before running flow direction and flow accumulation functions.