  The bifurcation of plane waves to localised structures is investigated in the
Dysthe equation, which incorporates the effects of mean flow and wave
steepening. Through the use of phase modulation techniques, it is demonstrated
that such occurrences may be described using a Korteweg - de Vries (KdV)
equation. The solitary wave solutions of this system form a qualitative
prototype for the bifurcating dynamics, and the role of mean flow and
steepening is then made clear through how they enter the amplitude and width of
these solitary waves. Additionally, higher order phase dynamics are
investigated, leading to increased nonlinear regimes which in turn have a more
profound impact on how the plane waves transform under defects in the phase.
