Rakaia is a town sited on the southern banks of the Rakaia River on the Canterbury Plains in New Zealand's South Island, approximately 57 k…Rakaia is a town sited on the southern banks of the Rakaia River on the Canterbury Plains in New Zealand's South Island, approximately 57 km south of Christchurch on State Highway 1 and the Main South Line. Immediately north of the township are New Zealand's longest road bridge and longest rail bridge, both of which cross the wide shingle beds of the braided river at this point. Both bridges are approximately 1,750 metres in length.