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Estuary types

Estuary types are a way of classifying New Zealand's coastal waters based on the Estuary Environment Classification (EEC) system.

From here you can find out about different kinds of estuaries, where they are located, their key physical properties and how to use this information with Coastal Explorer. 

The Estuary Environment Classification 

The EEC uses an estuary definition of: "A partially enclosed coastal body of water that is either permanently or periodically open to the sea in which the aquatic ecosystem is affected by the physical and chemical characteristics of both runoff from the land and inflow from the sea" 1,7.

This definition includes coastal landforms such as drowned river valleys, lagoons, coastal lakes, fjords, and river mouths. It also includes features variously named on maps as creeks, firths, inlets, gulfs, coves, rivers, bays, lagoons, harbours, streams, fjords, sounds, ports, arms, small craft retreats, havens, basins, and of course estuaries.

The EEC is a based on 'controlling factors' such as climate, ocean and river conditions, and catchment characteristics that cause differences in the physical and biological characteristics of estuaries. A full classification for an individual estuary will describe its hydrodynamic processes, its catchment geology and land cover characteristics.

Find out more about the system in these references

How the EEC is applied in Coastal Explorer

Coastal Explorer shows where estuaries with different hydrodynamic processes occur in New Zealand. The EEC assigns estuaries to 8 different classes based on:

  • the shape and volume (morphometry) of the water body,
  • the quantity of river flow entering the estuary and
  • the quantity of exchange of seawater between the estuary and the ocean.

These factors combine to to produce different kinds of mixing, circulation, stratification, sedimentation, and flushing. These classes are:

You can click the links above to find out about each estuary type.

GIS and the classification database of estuary properties have been used to map where the different classes of estuaries occur around the New Zealand coast. The 8 classes are denoted by different coloured icons in the Coastal Explorer views.

Estuary report cards

Clicking on the coloured icons in Coastal Explorer brings up estuary report cards which provide information on individual estuaries. They display a hydrodynamic classification and summary of the general properties associated with that class, along with a schematic showing plan and elevation view and an image for that estuary type. They also provide frequently asked for statistics for the estuary, relating to size, shape, hydrodynamic and catchment properties. About 430 New Zealand estuaries are classified in the system. 

The Waitaki River mouth, just north of Oamaru, South Island. [NIWA]
EEC hydrodynamic classes mapped for New Zealand.
EEC mapped for Banks Peninsula showing hydrodynamic, geology and land cover classes and the full classification.
Screenshot of an estuary report card from Coastal Explorer.