Rutines for converting runoff data into river data used by e.g hycom.

Environment variables:
ERA40_PATH : points to location of ERA40 data with runoff fields
TRIP_PATH  : points to location of TRIP data (can be found under Data in this dir)

Routines:
These three routines depend only on runoff and trip data :
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trip_paths   - mostly diagnostic routine to calculate largest river catchment basins 
               and grid cells with largest river flux
trip_weights - Calculates the mapping from a runoff grid (here ERA40) to TRIP grid. Must be run
               before trip_flow
trip_flow    - Calculates the transport of runoff water from its initial appearance through rivers
               and towards the sea. Uses ERA40 runoff data. Calculated on TRIP grid. Produces netcdf
               files with runoff, volume of water on land surface and river discharge


HYCOM specific routine 
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trip_tohycom - Uses output from trip_flow to calculate a hycom climatology 
               of river discharge in coastal grid cells.