 The difference is the sediment supplied by the Waimakariri River is a source for the coast's New Brighton spit due to the reversal of southern currents transporting sediment to the south.In contrast the Canterbury Bight has a combination of high energy environments and strong southern longshore currents that transport large amounts of sediment north, which can be classified as a sink, putting a deficit to the coasts sedimentary budget.As a result, there is erosion of the Canterbury Bight and a predominantly balanced New Brighton Spit.