A linear analysis of rotating stratified flow past a circular cylinder on an f-plane is made for moderate and strong stratification, i.e. for σS = O(E½) and σS = O(1) respectively. E is the Ekman number and σS is the product of the Prandtl number and the inverse rotational Froude number. The most striking result is that, for oncoming flows that are of one sign and possess vertical shear, reversed-flow regions can exist next to the cylinder. Depending on the degree of stratification, these backflow regions can occupy the inner part of the vertical boundary layer or can extend horizontally across distances comparable to the horizontal scale of the cylinder.

The equations for gravity waves on the free surface of a laterally unbounded inviscid fluid of uniform density and variable depth under the action of an external pressure are derived through Hamilton's principle on the assumption that the fluid moves in vertical columns. The resulting equations are equivalent to those of Green & Naghdi (1976). The conservation laws for energy, momentum and potential vorticity are inferred directly from symmetries of the Lagrangian. The potential vorticity vanishes in any flow that originates from rest; this leads to a canonical formulation in which the evolution equations are equivalent, for uniform depth, to Whitham's (1967) generalization of the Boussinesq equations, in which dispersion, but not nonlinearity, is assumed to be weak. The further approximation that nonlinearity and dispersion are comparably weak leads to a canonical form of Boussinesq's equations that conserves consistent approximations to energy, momentum (for a level bottom) and potential vorticity.