def maskFromDepth(depth, zCellTop):
  """
  Generates a "wet mask" for a z-coordinate model based on relative location of
  the ocean bottom to the upper interface of the cell.

  depth (2d) is positiveo
  zCellTop (scalar) is a negative position of the upper interface of the cell..
  """
  wet = 0*depth
  wet[depth>-zCellTop] = 1
  return wet