NZ Estuarine Environment Classification
About the classification
NZ estuary classification.
Banks classification.
Coromandel classification.
The Estuary Environment Classification (Hume et al. 2007; 2003) provides a framework for classifying New Zealand’s estuaries. This controlling factors classification is based on broad scale physical components of the landscape or ‘controlling factors’ such as climate, oceanic and riverine conditions, and catchment characteristics that cause or ‘control’ differences and similarities in the physical and biological characteristics of estuaries. The classification differentiates estuaries at 3 levels of detail. Level 1 differentiates global scale variation based on differences in climatic and oceanic processes, which are discriminated by the factors: latitude, oceanic basins and large landmasses. Level 2 differentiates estuaries into 8 categories (or estuary types ) on the basis of variation in estuary hydrodynamic processes, which are discriminated by estuary basin morphometry, river and oceanic forcing. Level 3 differentiates variation among estuaries that are due to catchment processes, which are discriminated by catchment geology and catchment land cover.
Estuaries are assigned class membership at each level of the classification by applying criteria in the form of decision rules to the database of assignment characteristics. GIS is then used to map the estuaries with classes being defined by colour at any level of the classification. The resulting map showing the distribution of various classes of estuaries around New Zealand provides a multi-scale spatial framework that is suitable for many environmental or conservation management applications.
A hydrodynamic classification of New Zealand’s estuaries (Source: Hume et al. 2007).
A hydrodynamic classification of estuaries on the Coromandel Peninsula and Banks Peninsula. New Zealand (Source: Hume et al. 2007).
Methodology and data sources
The classification was derived from a database populated with physical variables descriptive of climate, oceanic water mass, basin morphometry, oceanic forcing (tides), river forcing (freshwater inflow), characteristics of the contributing catchment (including topography, geology and land cover), and factors that vary within an estuary including depth, tidal currents, and wind waves. The database has over 50,000 cells relating to 440 estuaries. Data mining and computation using numerical and analytical models and GIS was used to derive the database. Variables were derived from various sources including NIWA’s DEM (30 m cell size) of New Zealand, the 1:50,000 Digital Topographic Database, New Zealand Land Resource Inventory (NZLRI), the New Zealand EEZ Tidal Model (Walters et al. 2001), digital files of the RNZN hydrographic charts, and various publications and reports.
Application of the classification
The classification uses a broad definition for estuaries to include the many different types of coastal water bodies that need to be managed. It follows Day’s (1981) variation of Pritchard’s (1967) definition and defines an estuary as: “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”. This definition includes estuary types and coastal water bodies described in other New Zealand classifications (e.g., Healy and Kirk 1982, Hume and Herdendorf 1986, 1993) as drowned river valleys, lagoons, coastal lakes, fjords, and river mouths. It includes features variously named on the NZMS 1:50,000 topographic maps as estuary, creek, firth, inlet, gulf, cove, river, bay, lagoon, harbour, stream, fjord, sound, port, arm, small craft retreat, haven, and basin.
The classification can be used to simplify the complexity of estuaries, so that differences and similarities can be characterised and ordered systematically and thereby providing an objective basis for treating different locations in a similar manner, extrapolating the results of studies between estuaries, and stratifying environments on the basis of their susceptibility and vulnerability to effects of development.
Further reading
Day JH. (ed) 1981. Estuarine ecology with particular reference to southern Africa. A.A. Balkema, Cape Town, 1981. 411pp.
Healy TR, Kirk RM. 1982. Coasts. Pp. 81-104 in Soons JM, Selby MJ, editors. Landforms of New Zealand. Longman Paul, Auckland, 1982. 402pp.
Hume TM, Herdendorf CE. 1993. On the use of empirical stability relationships for characterising inlets. Journal of Coastal Research 1993; 9: 413-422.
Hume TM, Herdendorf CE. 1988. A geomorphic classification of estuaries and its application to coastal resource management - A New Zealand example. Journal of Ocean and Shoreline Management 1988; 11: 249-274.
Hume T, Snelder T, Weatherhead M, Liefting R, Shankar U, Hicks M. 2003. A new approach to classifying New Zealand’s estuaries. Paper No. 66 in Kench P. and Hume T. (eds) Proceedings of Coasts & Ports Australasian Conference 2003, Auckland, New Zealand. 9p. CDRom ISBN 0-473-09832-6.
Hume T, Snelder T, Weatherhead M, Liefting R. 2007. A controlling factor approach to estuary classification. Journal of Ocean and Coastal Management. Volume 50, Issues 11-12, Pages 905-929. http://dx.doi.org/10.1016/j.ocecoaman.2007.05.009
Pritchard DW. 1967. Observation of circulation in coastal plain estuaries. In: Lauff GH, editor. Estuaries, Washington, DC: American Association for the Advancement of Science, 1967. p.3-5.
Walters RA, Goring DG, Bell RG. 2001. Ocean tides around New Zealand. New Zealand Journal of Marine & Freshwater Research 2001; 35: 567-779.