Autumn river water temperatures were mostly in the range 8-16 oC in the North Island and a little cooler in South Island (mostly below 12 oC and below 8 oC in some mountain-fed rivers). As is typical there was a weak trend of decreasing temperature moving south (increasingly latitude) and a stronger trend of decreasing temperature with increasing altitude. The temperature anomaly map for Autumn shows that river temperatures tended to be fairly typical over both islands, although rather warmer than typical in the South island. River temperatures were unusually warm in south Canterbury and in the Manawatu River, and unusually cold in the Ruamahanga River (southern North Island).
River water temperature, April - June 2015.
Temperature Anomaly, April - June 2015.
Visual clarity of rivers (April, May, June)
Characteristic visual clarity of New Zealand rivers ranges roughly 300-fold, reflecting the diversity of soil and rock types modified by land use and vegetation cover, while visual clarity in individual rivers varies widely with state-of-flow. Over the Autumn, rivers in New Zealand rivers ranged widely in clarity from <0.2 m (e.g. in the Waipaoa River in Gisborne district) to more than 6 m in several, mostly inland, high altitude, rivers in both main islands. The clarity ranking map shows that visual clarity was fairly typical in most rivers of the North Island. However, rivers in the NW and south of the South Island were unusually turbid, reflecting high flows, while rivers in south Canterbury were unusually clear (and warm) reflecting very low flows.