Euler's equations of motion in conjunction with the dynamic boundary c
ondition are manipulated to obtain exact (and approximate) alternative
momentum equations for nonlinear irrotational surface waves. The Airy
and Boussinesq equations are re-derived as demonstrative examples. A
fully nonlinear version of the improved Boussinesq equations is presen
ted as a new application of the proposed equations. Further use of the
equations in developing depth-integrated wave models, which are not n
ecessarily restricted to finite depths, is also pointed out. (C) 1998
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