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Human activities alter the natural flows in our water bodies

Taking water, creating diversions, dams, and bores, and using land are human activities that influence water flows. We use water for farming (irrigation and stock drinking water), power generation, drinking water, and industry. In some instances, our activities provide benefits in addition to the supply of water – for example, artificial lakes created by dams have the potential to create new recreation opportunities.

Flow regime influences a river’s physical form by affecting how sediment is transported and deposited. A flow regime is important because flow combines with river topography to influence the habitat available for freshwater species. Although ecological processes are affected by many factors, flow is important because it influences food delivery, nutrient transport, and channel connectivity. It has been argued that freshwater species have evolved their life cycles in response to natural flow regimes (Bunn & Arthington, 2002). However, examples where changes to natural flow regimes have maintained, or even improved, in-stream values in some New Zealand rivers have also been reported (Jowett & Biggs, 2008). Altered flows can potentially influence fish abundance (Jowett et al, 2005), fish migration (Boubée et al, 2001), fish spawning (McDowall, 1990), the availability of physical habitat for fish (Jowett & Richardson, 1995), and invertebrate communities (Greenwood & Booker, 2014). If the flushing flows of rivers are reduced, algae and fine sediment can build up, reducing amenity and recreation values and degrading the habitat of freshwater species (Biggs, 2000). Māori assert their tribal identity in relation to water bodies, with each water body having its own mauri. Altered flows and water levels can degrade the mauri and mahinga kai values of water bodies (Tipa & Teirney, 2006).

Hydroelectricity and irrigation are the largest consented uses of freshwater takes

For more than a century, we have been using water resources for public use and agriculture, and to produce energy. The number of water takes, together with their position in the river network, rate of take, and timing, combine to determine the impact on flow regimes. Larger impacts on flow occur when larger volumes of water are taken for consumption (meaning the water is used and not returned to the site where the water was taken) from multiple locations, particularly in dry periods.

Water can be taken directly from surface water or from the groundwater system by pumping. Surface water and groundwater are often connected, so taking water from one affects both. However, quantifying the timing and extent of connection between groundwater takes and river flow depletion can be difficult. Resource consent data from all 16 regional and unitary councils show that groundwater takes are particularly common in Canterbury, which accounts for 56 percent of total consented groundwater volume (Booker et al, 2016a).

Hydroelectricity generation and irrigation are our largest consented uses of fresh water, with the remainder allocated for industrial, drinking, stock water, and other minor purposes (Booker et al, 2016a). Irrigation in New Zealand has allowed for the significant expansion of a range of farming systems (New Zealand Institute of Economic Research (NZIER) & AgFirst Consultants NZ, 2014). Irrigation gives a greater reliability of production, increased yields, and improved quality of production (NZIER & AgFirst Consultants NZ, 2014).

Water taken for hydroelectricity production is generally non-consumptive, meaning the water is returned to downstream water bodies after use (two notable exceptions are the South Island’s Manapouri Power Station, which discharges directly to the ocean in Doubtful Sound Fiordland, and augmentation of the Waikato River from adjacent catchments in the North Island). However, water for hydroelectricity production is often stored behind dams, which alter river flow patterns downstream (Duncan & Woods, 2004).

The hydroelectric potential of New Zealand was recognised in the early 1900s, when construction of the first government scheme was completed in 1914 (Young et al, 2004). New Zealand relies on a plentiful supply of water for its energy supply. Hydroelectricity is our main source of renewable energy, accounting for more than 56 percent of electricity generation in 2015, returning $586 million to hydroelectricity operators (Stats NZ, 2017).

Water consented for irrigation varies by region, with Canterbury accounting for nearly 65 percent of the total consented volume of water nationally (see figure 21). A further 9 percent of the consented volume is in Marlborough, followed by 7 percent in Otago (although 53 percent of surface water consents in Otago had missing values for consented volume, so Otago consented volumes may account for a higher proportion than is expressed here) (Booker et al, 2016a).

Figure 21

number of consented freshwater takes by region and volume of consented freshwater takes by region for 2013–14
Click here to enlarge view

This graph shows number of consented freshwater takes by region and volume of consented freshwater takes by region for 2013–14. Visit the MfE data service for the full breakdown of the data.

For more detail see Environmental indicators Te taiao AotearoaValue of water resources used for hydroelectric generation [Stats NZ] and Consented freshwater takes [Stats NZ].

We do not know our actual water use but irrigation has the greatest potential to alter river flows

The Resource Management (Measurement and Reporting of Water Takes) Regulations 2010 (the Regulations) requires holders of consents for water takes over five litres per second to install meters and provide a continuous record of water takes, annually, to their regional council.

Takes of less than five litres per second are not covered by the Regulations. Many water takes for permitted activities do not require a resource consent, such as taking water for domestic use, firefighting, and stock drinking. Regional councils use various models and methods for estimating permitted takes, but further work is needed to build a consistent approach for robust national estimates.

Implementing the Regulations varied across New Zealand. In some regions, installing and verifying meters took longer than expected, primarily due to a shortage of accredited providers. Where this is an issue, regional councils used accredited providers from neighbouring regions. The Regulations were implemented in a staged way, with the final stage (takes of 5–10 litres per second) required since November 2016. Data quality and completeness are therefore currently mixed across the regions, meaning we cannot report on actual metered water takes at a national scale in this report (see Water availability in Canterbury for a case study on actual water use).

Due to inconsistent data on actual water takes nationally, we rely on consented water takes to indicate the potential impacts of freshwater takes on our rivers. The potential impact on river flows as a result of all upstream consented takes was calculated by summing the consented rates of all upstream consented takes and then dividing by the estimated long-term natural median flow (Booker et al, 2016a).

The cumulative effect of consented water takes on downstream river flows showed that water takes for irrigation have the highest potential to cause widespread reductions in downstream river flows, compared with other water uses (see figure 22 and figure 23) (Booker et al, 2016a). This is especially noticeable in Canterbury and Hawke’s Bay where many consents are from groundwater as well as surface water. Note that estimating river flow depletion resulting from groundwater takes is uncertain. Limited evidence also suggests that not all consents are used to their full allocation, and many consents include rules to limit the rate of take during low-flow periods. The figures presented here show a worst-case scenario for river-flow depletion.

Water consented for hydroelectricity, industrial, and drinking uses may also have impacts on downstream flows, but these are concentrated in a few catchments. For example, Auckland experienced temporary drinking-water shortages in the past, and as its population continues to grow, new sources of water are needed (Auckland Council, 2013).

Demand for irrigation is higher in summer and in drought years (Woodward et al, 2001), which can exacerbate water availability issues. To protect the environment during periods of naturally low flow and when there is the greatest demand for water, many councils have restricted consents so that water cannot be taken when river flow at a control site falls below a certain flow rate. These restrictions are complex, and are not accounted for in our estimates of the impact of water takes on river flows. The natural timing of low flows also does not always coincide with peak water demand – freezing creates low flows in winter for cold catchments (eg Poyck et al, 2011).

Water availability in Canterbury

The quality and quantity of data describing actual water use are improving following recent changes to legislation. Canterbury is one region that has some data available on actual water use. For the 2013–14 water year (July to June), their data showed large differences between consented takes (how much water a user is allowed to take) and recorded takes (how much water the user actually took). This indicated that users who supplied records did not use their full allocation, particularly in early and late summer. However, in late February recorded use was near the maximum allowable use (Environment Canterbury puts restrictions on use when flows drop below a certain level). A large proportion of the consents had no associated records, so for many users, we do not know how much water they took.

The available data on water use suggested many water-user behaviours. Some records indicated they took consistently far less than their consented values even after restrictions were applied – they complied, but also had ‘headroom’ (ie more water allocated than used) within their consents. Some users had occasional recorded takes that exceeded their consented or restricted takes – they complied on average, occasionally were non-compliant, but still had some ‘headroom’. Other records showed users consistently had recorded takes that met or exceeded their consented or restricted takes – they were consistently non-compliant and had no ‘headroom’ within their current consent conditions (except perhaps in mid-winter). For a few users, recorded values indicated consistently greater takes than their consented or restricted takes – they appeared to be consistently non-compliant and had no ‘headroom’ within their current consents, potentially denying other users of the opportunity to take water.

Source: Booker et al, 2017

For more detail see Environmental indicators Te taiao AotearoaConsented freshwater takes [Stats NZ].

Figure 22

shows the estimated potential flow reduction as a proportion of the natural median flow as a result of all upstream consented water takes for 2013–14
Click to enlarge view

This map shows the estimated potential flow reduction as a proportion of the natural median flow as a result of all upstream consented water takes for 2013–14. Visit the MfE data service for the full breakdown of the data.

Note: Positive values indicate the potential flow depletion resulting from upstream consented takes, while negative values indicate flow augmentation (eg consents for hydroelectricity that return water to a location different from where it was originally taken from). These maps represent a worst-case-scenario of river flow depletion because they do not take into account restrictions on water takes and all groundwater takes were assumed to eventually result in river flow depletion. The median flow refers to modelled naturalised median flows, rather than actual flows. The effects of 53 percent of Otago consents are not included because they had missing values.

Figure 23

four maps; one for all surface water takes, one for irrigation surface water takes, one for all groundwater takes, and one for groundwater irrigation takes
Click to enlarge view
 

This figure shows four maps; one for all surface water takes, one for irrigation surface water takes, one for all groundwater takes, and one for groundwater irrigation takes. All four maps show the estimated potential flow reduction as a proportion of the natural median flow as a results of all upstream consented water takes for 2013–14. Visit the MfE data service for the full breakdown of the data.

Note: Positive values indicate the potential flow depletion resulting from upstream consented takes, while negative values indicate flow augmentation (eg consents for hydroelectricity that return water to a location different from where it was originally taken from). These maps represent a worst-case-scenario of river flow depletion because they do not take into account restrictions on water takes and all groundwater takes were assumed to eventually result in river flow depletion. The median flow refers to modelled naturalised median flows, rather than actual flows. The effects of 53 percent of Otago consents are not included because they had missing values.