Defining the River Corridor. It is important to define precisely the area of the Floodplain that comprises the River Corridor. The Otaki Floodplain Management Plan provided a base definition to work from, for the Hutt River Corridor. That definition is summarised below: The River Corridor is the minimum area that is able to contain a major flood and. pass water safely to the sea. . The outer limit of the River Corridor, where not adjacent to the ponding and overflow path, is the. extent of the design flood. .