the width and height of which determine the pattern of the waterfall .Most arrangements require an adjustable lip at the beginning of the overflow and a "weir" edge on the other side, With wide waterfalls, the lip should be adjusted perfectly level to prevent the water film from breaking up It is also important that leaves and dirt do not collect on either the "fall-away" or lip, This can be prevented by a cover, Arrangements frequently combine fountains with waterfalls, with a succession of basins placed on intermediate pedestals one above the other and getting smaller in diameter as they get higher. Water, fed into the top basin, flows in steps down to the lower, larger basins, resulting in a neatly proportioned display of constant water curtains.