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Historic Freshwater State

Water quality

Surface Water Quality – WQI measures

Surface water, being above ground waterways, are easily recognizable across the Marlborough landscape – such as our iconic braided rivers. Surface water courses gain their flow through catchment areas as well as underground springs in some cases. A catchment is the area of land from which all rainfall and streams flows out into a river, a lake or the sea. The catchment of large rivers, such as the Awatere River, can be divided into smaller sub-catchments, which usually represent the tributaries.

The Surface Water Quality State of the Environment (SOE) monitoring has been operational in Marlborough since 2007. The programme measures 56 sites regionally, three of which are in the Awatere FMU.

The Water Quality Index (WQI) serves as a consolidated score reflecting the quality of river water. It is derived from nine chemical and physical parameters measured on a monthly basis. The WQI ranges from 0 to 100 with higher values indicating better water quality. The WQI simplifies comparisons of water quality across various waterways and serves as a valuable tool for identifying degraded waterways and prioritising improvement actions.

The five index classes represent water quality, with “marginal” and “poor” categories requiring improvement. The higher the index number, the better the water quality and accordingly the closer to “excellent” WQI rating. Read more about our surface water SOE monitoring programme below:

Go to the SOE monitoring programme page

WQI graph, South Marlborough 2007 - 2015

The table below shows the historical WQI indices for the Awatere FMU monitoring sites. This data is also shown on the graph to the right – please note this graph is historic; the Waima River and Flaxbourne River are not part of this FMU area. The WQI for the Black Birch, Mid Awatere and Lower Awatere monitoring sites are summarised into the chart.

We can see from the graph that the WQI at Black Birch site has remained unchanged or improving. In contrast, the mid and lower Awatere WQI indices gradually declined in the mid-2010s. We can also see from the below chart that a large proportion of the indices were in the ‘marginal’ or ‘poor’ categories.

The 2016 surface water SOE report provides insight as to the decline in water quality at the mid and lower Awatere monitoring sites at this time:

“Black Birch Stream flows into the Awatere River, which has substantially poorer water quality. However, the parameters which cause the greatest reduction in the Water Quality Index are elevated predominantly due to natural causes. High turbidity and pH values are the result of high mudstone and limestone content in the geology of the Awatere River catchment. Nevertheless, there is a large amount of infrastructure associated with irrigation water takes in the lower Awatere.

Maintenance of these intakes generally causes significant increases of turbidity during the work. Trend analysis shows a significant increase in turbidity for both sampling sites, however, which indicates that the source is likely to be located in the upper catchment. Since trend data is flow adjusted, the increase in turbidity is not a result of changes in flows during sampling. The majority of the upper catchment is extensively farmed pasture and it is unclear what is causing the increased turbidity, but greater erosion is the most likely explanation. The increase in turbidity caused a significant reduction in the Water Quality Indices for the two Awatere River sites, which have shifted from the marginal into the poor category.”

Awatere SOE monitoring sites – historic quality measures

Monitoring site

2007-2009

2010-2012

2011-2013

2012-2014

2014-2016

2016-2018

Black Birch

Not measured

Excellent

Good

Good

Good

Good

Lower Awatere (at River Mouth)

Marginal

Marginal

Poor

Poor

Poor

Poor

Mid Awatere (Medway confluence)

Marginal

Marginal

Marginal

Marginal

Poor

Poor

The historic quality measures in the above table are further summarised across all years and for all three sites into the below chart. We can see from the chart that the majority of WQI measures are either marginal or poor, with a small number of excellent or good measures. The latest WQI summary up to 2022 is in the Awatere Current Freshwater State page.

Go to the Awatere Current Freshwater State page

WQI chart summary, Awatere 2007-2018

Ground Water Quality

The impermeable nature of the local geology generally precludes high-yielding aquifers in the lower Awatere Valley. Groundwater is instead supplied from shallow wells in thin gravel beds overlying the distinctive mudstone papa which represents the base of the aquifer and doesn’t contain groundwater itself. Compared to the Wairau aquifer, well yields are low and rely on recharge from nearby streams.

Accordingly, there are no true groundwater aquifers in this FMU. For this reason, water quality is primarily monitored through the surface water monitoring network.

Water quantity

Due to the low amount of rainfall in the area, the associated mean flow in the Awatere River is considerably less than northern rivers despite having a much larger catchment size.

Historically, Awatere surface water was mainly used for domestic and stock water purposes. It was not used for large scale irrigation, frost fighting, or private damming until much more recently. The significant increases in irrigation quantity coincided with the rise in viticulture development.

Surface water quantity is measured through river flow rates (m3/sec) which are measured continuously. In the Awatere FMU, this has been measured at the Lower and Mid Awatere sites since 2020 and 1977 respectively. Given the length of recording, the Mid Awatere (Awatere at Awapiri) site gives an excellent representation of water quantity over time.

Awatere surface flow sites – water quantity

Monitoring site

Catchment area (monitoring site only)

Mean flow

7-day MALF (mean annual low flow)

Mean annual flood flow

Lowest recorded

Highest recorded

Mid Awatere

983 km²

14 m³/sec

3.06 m³/sec

180 m3/sec

1.49 m3/sec

500 m3/sec

The mean flow at the Mid Awatere site is 14 m³/sec, which is a mean over the entire time the site has been measured. When compared rivers further north in the region, the Awatere has a much lower mean flow – the Wairau at Tuamarina has a mean flow of 100 m³/sec, significantly higher than the Awatere. The Branch River at Weir Intake has mean flow of 19.6 m³/sec, also in the Wairau FMU. Interestingly, the Rai River is closer in terms of mean flow, being 11.4 m³/sec. These comparisons assist with considerations of scale, particularly in comparing the Awatere to the Wairau in terms of the volume of water in the river.

The 7 day mean annual low flow (MALF) is an important measure, as this shows the mean flow during an average summer dry period. Irrigators should consider this flow rate in the context of their irrigation consents and associated flow cut off conditions, as this flow rate is occurring during the summer days when irrigation requirements are high.

Group water schemes

Some of the large water use schemes in this FMU can be summarised below:

  • Awatere Water Supply (Birch Water Scheme) extension 1962
  • Blind River Irrigation Scheme commencement (BRIL) 2006
  • Awatere Irrigation Scheme commencement (AIL) 2009
  • Seddon Water Treatment Plant 2019

These are a mixture of private and council owned schemes.

Special investigation – Potential effects of Infiltration Galleries on the Awatere River 2016

Read the reports in full here

The Awatere River has a naturally elevated turbidity for much of the year due to fine suspended sediments, mainly derived from the highly erodible underlying geology of the mid-catchment.

High suspended sediment loads in the river cause problems for water abstractors. Fine sediment drawn into irrigation infrastructure can increase wear on pumps, block filters and irrigation drippers and so forth. Infiltration gallery intakes are perceived to offer a potential solution to these problems associated with fine sediment.

The 2016 report was commissioned to consider potential effects of instream works associated with infiltration gallery water takes in the Awatere River, including the possibility of cumulative effects arising from maintenance of multiple gallery intakes from the river.

Concerns were raised over the potential adverse ecological effects of instream works associated with the construction and maintenance of infiltration galleries in the Awatere River. In particular, the potential for cumulative effects resulting from maintenance of multiple galleries, such as habitat disturbance and interruption of spawning and fish passage. The 2016 report was commissioned to consider these potential effects.

The report produced several recommendations, including gathering more definitive data on instream gallery works, continuous turbidity monitoring, and sedimentation monitoring and control measures.

The completion of this report again highlighted the need for ongoing management of riverbed water intake structures. This conclusion supports the ongoing work of the Awatere Water Users Group (AWUG) who continue to work with the council and local experts to recognise ongoing improvements in techniques and technologies in riverbed activities by water users over time, the adaptive management of responding to changing environmental conditions, and future changes to the legal statutory requirements of waters users. The good management practices recommended are seen as an integrated package and not singular measures; these are contained in a continually updated document which has been in use since 2013.

The AWUG document does not replace the requirement for an appropriate resource consent for riverbed activities but does assist with informing water users with information and education for developing robust management strategies for their riverbed activities under a site specific management plan.

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