A geomorphic classification of estuaries and its application to coastal resource management—A New Zealand example

Abstract

This paper describes an estuarine classification scheme developed for a wide variety of New Zealand estuaries that has application to coastal resource management. Estuaries are grouped using existing geological and topographic map and air photograph data bases complimented by field reconnaissance. Estuaries are grouped into five classes, and these reflect the primary process that shaped the basin that forms the estuary namely: (1) fluvial erosion, (2) marine/fluvial erosion, (3) tectonic, (4) volcanic, and (5) glacial. These classes are subdivided on a morphologic basis into 16 types, which reflect catchment and coastal hydrologic and sedimentologic processes. Fluvial origin estuaries include unrestricted inlets, headland enclosed inlets, barrier-enclosed lagoons (double-spit, single-spit, tombolo, island and beach barriers) and river mouth (straight-banked, spit-lagoon and deltaic) types. Estuaries of marine/fluvial erosion origin are coastal embayments. Estuaries of tectonic origin include fault defined embayments (inlet width <2 km) and large diastrophic embayments of more complex origin (inlet widths >5 km). Explosion craters are of volcanic origin, while glacial estuaries are of a glacial origin. Compound estuaries are formed from two or more of the basic types. Relationships between inlet throat dimensions and tidal prism support the scheme structure.