Water quality maps and information, July to September 2013

River water temperatures and visual clarity of rivers.

River water temperatures (JAS)

Winter river water temperatures were mostly in the range 4-12oC in both islands and a little higher in the north and east of North Island. There are weak trends of decreasing temperature moving south (increasingly latitude), and decreasing temperature with increasing altitude (moving into mountainous areas) as is typical. The temperature anomaly map shows that river temperatures were normal or somewhat higher than normal for winter, particularly in lower North Island and large parts of South Island. The Waipaoa River (East Cape, North island) was unusually cool, and the upper Taieri River (Otago) unusually warm. 

Visual clarity of rivers (JAS)

Visual clarity of rivers over winter ranged widely (from <0.2m to >6 m). This visual clarity range reflects the wide range of soil and rock types and vegetation cover in New Zealand, with rivers draining livestock pasture being characteristically less clear than rivers in forest catchments. The clarity ranking map shows that many rivers deviated appreciably from typical visual clarity. There was little regional pattern, although rivers in Bay of Plenty and elsewhere in central North Island tended to be unusually clear. The departures from normality usually reflect flow conditions, since rivers are comparatively clear at low flow. 

Temperature, July to Septermber 2013. [NIWA]