Waimakariri Bridge is a location on the Midland Line. It is one of three crossings that the Kiwirail network has historically made of the river, all on different lines; the others being the Main North Line near Kaiapoi, and the Oxford Branch near Bexley (closed in 1930 but the bridge still stands today). Here is the overview map.
There are two key features of this location: the bridge itself which was replaced in the late 1970s on a new alignment; and the ballast pit on the north bank of the river.
The new bridge is concrete and was built on a new alignment slightly easing the curvature here (14 chains radius).
On the north side was the ballast pit.
Development of the Waimakariri Ballast Pit began in 1941 due to an anticipated requirement of large scale reballasting work being needed on the Midland Line in the coming years, however it was not until 1944 that the pit was fully in operation with a dragline and crushing plant. Operations at the pit were suspended about 1953 and the plant was removed the following year. The date at which the site was finally closed off and cleared has not been ascertained. The historical aerial photos used in these comparisons were taken in 1966 at which time track was still in place in the two locations shown.