  In this paper we present the full classification of the symmetry-invariant
solutions for the Gibbons--Tsarev equation. Then we use these solutions to
construct explicit expressions for reductions of Benney's moments equations, to
get solutions of Pavlov's equation, and to find integrable reductions of the
Ferapontov--Huard--Zhang system, which describes implicit two-phase solutions
of the dKP equation.
