newcells: Boolean

Since the advection of momentum is not conservative in the upper cells, the velocity in the upper cells can be adjusted to ensure that

$$U_{top}^{n+1}\Delta z_{top}^{n+1} = U_{top}^{n}\Delta z_{top}^{n} .$$

This should be used with caution and results should be checked to make sure this does not alter them significantly. Otherwise the upper layer depth is too small relative ot the free surface motions.
(0): Do not adjust upper layer cells, (1): Adjust upper layer cells.