This paper is concerned with the velocity in the boundary layer of an estuary during a tidal cycle; the estuary considered has negligible salinity effect. The problem reduces to solving the usual non-steady boundary layer equations if it is assumed that (a) flow is two-dimensional, with a horizontal bed at any cross-section, and (b) little variation in breadth of the estuary in the boundary layer region. Further, the eddy viscosity is considered constant; thus the boundary layer equations are the same as those for a laminar layer except that they have an enhanced coefficient of viscosity due to turbulence....