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Water quantity and flows

Top finding

More than half the water allocated (or consented) by councils is for irrigation, but we do not know how much of this is actually used.

What is happening?

Humans have been taking water and modifying water bodies for agriculture and urbanisation, and to produce energy and protect against flooding, which have resulted in altered flow regimes. The most widespread cause of altered river flow from water takes appears to be irrigation, although other uses such as hydroelectricity are important in some catchments. We currently do not have national-scale data on water use, and have relied on consented information for this analysis. Climate change is predicted to exacerbate pressures on water flows and the availability of water.

Why does it matter?

Flow reductions result in less water available for ecosystems and human use. Our current economic dependence on primary industries means we are relying on taking water for irrigation. Altered flows can negatively affect the health and mauri (life force) of freshwater ecosystems by negatively impacting on the habitats of freshwater species, landscape aesthetics, and the suitability of our freshwater environments for recreation.

Water quantity refers to the amount of water present in rivers, streams, lakes, wetlands, aquifers, and glaciers. Flow is the volume of water passing a point over a certain time, which indicates the availability of water for people and the environment. There needs to be a balance between providing water for public, industrial, and agricultural uses and ensuring the protection of freshwater ecosystem functions.

The timing and volume of water (also known as ‘flow regime’) are components of a healthy freshwater system and are linked to water quality. For example, if freshwater flows are low, little water is available to dilute nutrients and other contaminants that negatively affect water quality.

In this chapter we focus on how water flows are influenced by climate patterns. We also discuss some human activities that influence the flows in our water bodies. Changes in glacier volume will be covered in Our atmosphere and climate 2017, to be published in October 2017.

This chapter covers: