Types of Rivers in Tasman

The Influence of Climate

In Tasman District most rivers are shaped by a ‘cool wet’ and ‘cool extremely-wet’ climate (45% of all rivers each, respectively). ‘Cool’ means mean annual temperatures less than 12oC, ‘wet’ means annual precipitation of 500-1500mm and ‘extremely wet’ is >1500mm annual precipitation. Small coastal streams between Richmond and Motueka are the only waterways in the district influenced by a ‘warm dry’ climate (2.5% of all streams). Inland from these streams in the Moutere Hill country, streams are described as being ‘cool and dry’ (about 3% of all streams). Several small coastal streams in Golden Bay are influenced by a ‘warm wet’ climate (3% of all streams).

The Influence of Source of Flow

Just over half the streams in the district are fed by hill country catchments, a quarter fed by mountainous areas (>1000m) and most of the remainder are lowland-fed with a few spring-fed streams. Hill-fed streams in the Moutere area tend to have intermittent or ephemeral flow.

There are a large number of karst springs in the district particularly in Mt Arthur marble country. Waikoropupu Springs is one of the world’s largest cold-water springs with a mean flow of 13.2 m3/sec with a stable mean temperature of 11.7oC. The spring arises from one of the most important karst aquifers in New Zealand in terms of volume of water storage, the Takaka Valley. The marble aquifer extents for 180m2 and is well over 500m thick. The average flow in the Takaka River is 16.1 m3/sec but it loses up to 10-11 m3/sec in its middle reaches. The river regularly dries up in summer in these mid reaches. Alluvial springs exist near the Takaka, Motueka and Waimea River deltas.

The Influence of Geology

Geology plays an important role in shaping aquatic communities, particularly in the upper Motueka catchment where there are high concentrations of the heavy metals iron, nickel and chromium in stream sediment. This is due to weathering of ultramafic rock in the Red Hills. This occurs to a lesser extent in other streams draining the Barnicoat and Bryant Rangess in the eastern part of the district. Rivers draining marble geology have substantial low flows compared to Moutere Gravels.

The Influence of Land Use

60% of streams in Tasman District are influenced primarily by catchments covered in indigenous forest. Almost two-thirds of the district is protected in conservation estate. This includes 9% of land covered in tussock and bare rock.  Of the ‘working lands’, 16% of streams are heavily influenced by pastoral land use and 9% by exotic forestry.