Practical limit on number of pathline records

[aprovost-usgs]

After MODPATH does its tracking calculations, it consolidates the pathline results. If the total count of such results exceeds the maximum value that can be represented by a default FORTRAN integer variable, about 2.1 billion, incrementing the integer counter past that limit results in a nonsensical, negative value, and a subsequent attempt to read from a file at that ‘negative position’ results in an error. Declaring that counter and any related integers as INTEGER(KIND=8) would extend the practical limit on the number of records. (Issue identified by DS.)

[aprovost-usgs]

The number of pathline results that could be processed (consolidated) after tracking was complete was limited by the fact that certain variables used to store integer-valued positions within files were declared simply as INTEGER and could therefore accommodate values only up to about 2 billion. The relevant variables have been identified and changed to INTEGER(kind=8), so they can now accommodate values up to about 9 quintillion. (However, note that other practical limitations on the number of pathline results may come into play before the new, extended limit on file positions is reached.) DS had kindly provided an example problem for which the file position count is about 2.9 billion - in excess of the previous limit, which caused a runtime error. The updated code runs this example problem to normal completion. The updated source code has been posted (commit bc2599c), and we're working on a USGS release that includes this update.