  Coasts are obstructions to the classical derivation of continuously
stratified quasigeostrophic equations, due to possible resonances between slow
internal coastally trapped Kelvin waves and anticyclones. [Deremble et al Ocean
Modelling 2017] proposed a coupled model between a quasigeostrophic interior
and boundary layer Kelvin wave dynamics. We revisit the derivation of this
model, paying particular attention to conservation laws. We find that
quasigeostrophic energy is conserved despite the existence of Kelvin wave
shocks in the boundary layer. The effect of those shocks is to change the
global distribution of potential vorticity, and, consequently the interior flow
structure. In that respect, we show that there is an active control of the
boundary region on the interior flow.
