The outlet of tunnel 4 is visible on the right centre of the picture above. The stream bed is that of the Ngatuhoa river and the water is diverted into tunnel 5 leading into Lake Mangaonui.
Overhead, in the picture above, is an access road bridge. The weir catches the natural flow along the upper Mangapapa river as well as serving to divert the flow from tunnel 2 to tunnel 3.
