  We use a 1d model of a superfluid based on the Gross-Pitaevskii Lagrangian to
illustrate a general numerical method designed to find quantum tunneling rates
in extended bosonic systems. Specifically, we study flow past an obstacle and
directly solve the imaginary time dynamics to find the ``bounce'' solution
connected with the decay of the metastable laminar state via phase slip
nucleation. The action for the tunneling confuguration goes to zero at the
threshold (in superfluid velocity) for classical production of these slips.
Applications to other processes are briefly discussed.
