Trying to understand much shorter time-step from PISM than from Matlab codes.  Probable issue: periodic differencing across edge of computational domain of b(x,y) and P(x,y) to generate water velocity V in PISMLakesHydrology and in PISMDistributedHydrology.  (This differencing is avoided in codes in hydrolakes/matlab/.)  Additionally it probably makes sense to implement 'outline' so that (e.g.) in the nbreen example we can only run the hydrology in a defined basin.  Roughly these are the no_model_mask and ftt_mask issues reappearing in the hydrology context.  So I guess they should be dealt with the same way.