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Introduction to Physiographics

Physiographic zones help us to better understand how contaminants move through the landscape. Each zone has common attributes that influence water quality, such as climate, topography, geology and soil type.

What are the zones?

There are nine physiographic zones for Southland:

Want an explanation from a scientist?

Hear Dr Clint Rissmann speak about the different physiographic zones on our YouTube channel.

Zones and contaminants

Zones differ in the way sediment, microbes, and nutrients (such as nitrogen and phosphorus) build up and move through the soil, through areas of groundwater, and into our rivers and streams.

For example, high levels of nitrogen in groundwater are a problem in some areas but not others. The science behind physiographic zones helps to explain why.

How do contaminants move?

Contaminants can move from the land to waterways via:

  1. overland flow (or surface runoff)
  2. artificial drainage – e.g. tile drains and mole pipe drainage
  3. deep drainage (or leaching) - of either nitrogen or phosphorus to groundwater
  4. lateral drainage (or horizontal movement through soil) - of phosphorus and microbes

These key transport pathways for contaminants differ for each physiographic zone. For example in Old Mataura it’s deep drainage, and in Alpine it’s overland flow.

Variants – what are they?

Some zones have more than one main transport pathway. These areas are called ‘variants’.

There are two types of variants:

  1. Overland flow (o) – in areas that tend to have steeper slopes
  2. Artificial drainage (a) – in areas that have artificial drainage

For example, the Bedrock/Hill Country zone has an overland flow variant and artificial drainage variant (see below).

Why are variants important?

Variants have an impact on which good management practices you’ll need to consider as part of your farm environmental management plan.

Find out more about Good management practices and see our range of factsheets.

Find out more about the proposed Southland Water and Land Plan.

What zones have variants?

The physiographic zones with variants are:

  • Bedrock/Hill Country – (o) and (a) variants;
  • Gleyed – (o) variant;
  • Lignite/Marine Terraces – (o) and (a) variants;
  • Oxidising – (o) and (a) variants;
  • Riverine – (o) variant.

View variants on our map

You can view variants on our physiographic zones map.

Variants are shown as lighter and darker shades of their physiographic zone colour. For example, Lignite/Marine Terraces is purple, the (a) variant is lighter purple, and the (o) variant is darker purple.