“…Here this coupled problem is considered with a shallow-water rigid-lid model for the two-layer fluid. There has been a vast amount of work on the two-layer model in open systems, and papers that have influenced the current theory are [2,9,10,11,12,15,17,21,22,26,27,28,29,32,34,35,37,41,42]. However the principal interest here is in closed systems.…”