Try creating a symbolic link from so.1 to the so.3 file.
Also - although it works gdplot2 is now defunct - be sure you use gdplot3.
From: "Kevin Lux"
Date: 12/31/2008 04:57AM
Subject: [gembud] libgfortran.so.1 not found
I installed the gempak 5.11 binary on my 64-bit system running kubuntu. I
added the gfortran-4.3 package, too. When I try to run something like gdcntr
or gdplot2, I get a message saying that the libgfortran.so.1 file doesn't
exist. The message is right because I only have libgfortran.so.3 where the
.so.1 version should be. How do I get around this? Can I just rename the file?