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 Wairau River, can be divided into smaller sub-catchments, which usually represent the tributaries.
Groundwater and aquifers are an important part of the Marlborough hydrological process. The 2011 book “Groundwaters of Marlborough”, published by MDC is a compilation of extensive research into the community knowledge of groundwater resources at the time. With a focus on aquifer science and hydrology, this was an update on the 1988 version which was similarly extensive and part of a series dedicated to underground water. The book continues to be a valuable resource and is available in full on the this website:
Go to the Reports and Special Investigations page
Surface Water Quality
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 Wairau, 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, 17 of which are in the Wairau 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 SOE monitoring programme below:
Go to the State of the Environment Reporting page
The graphs on this page show the various waterways and their historic WQI, which are varied across all the monitoring sites.
We can see a number of monitoring sites show decreases in WQI over this time. Decreases of note include the Upper Wairau (top graph), Wairau Diversion and Tuamarina River (middle graph), and Doctor’s Creek (bottom graph). The 2016 Surface Water State of the Environment Surface Water Quality Monitoring Report discusses these trends and results for the wider Wairau area as below:
“The Water Quality Index for the Upper Wairau River had been in the good category in the past but has declined considerably in recent years. Analysis in an earlier report showed that the increase of turbidity is a result of higher flows during sampling. A similar phenomenon was also identified for the Branch River. Unlike Water Quality Index data, the data used for trend analysis is flow adjusted. Trend analysis, done as part of this report, identified an increasing trend for turbidity in the Branch River, but not the Upper Wairau River. This indicates that some of the increases in the Branch River are not flow related. Recent harvesting of production forestry in the catchment is a possible source of additional fine sediment in this waterway.”
“Analysis of nitrate data revealed an increasing trend over the last five years for a number of sites north of the Wairau River. The wide range of this phenomenon indicates that a change in rainfall patterns is the most likely explanation. Most spring-fed streams show a significant decrease in nitrate concentrations, which can be linked to the widespread conversion of pastures into vineyards in the lower Wairau catchment.”
“Turbidity is also the most significant parameter influencing the Water Quality Index [for specific monitoring sites]… High turbidity in the Tuamarina River was the result of exceptionally large floods in 2013, causing extensive scouring and bank erosion in the lower reaches.”
“E. coli data were also analysed for trends and results show increases in concentrations for a number of sites, including the Taylor River … mid Ōpaoa, Spring Creek … and the Wairau Diversion. Investigations of the Taylor River have linked the faecal contamination to ducks, dogs and recently also to human sewage entering the river due to infrastructure damaged by recent earthquakes. For the other waterways investigation similar to those undertaken in the Taylor River would be needed to identify the causes of increased E. coli concentrations.”
You can read the 2016 SOE report in full below:
Go to SOE Surface Water Quality Monitoring Report 2016
Wairau FMU SOE surface water monitoring sites – historic quality measures | ||||||
|---|---|---|---|---|---|---|
Monitoring site | 2007-2009 | 2010-2012 | 2011-2013 | 2012-2014 | 2014-2016 | 2016-2018 |
Branch River | N/A | Fair | Fair | Fair | Good | Good |
Upper Wairau | Good | Good | Good | Fair | Fair | Fair |
Mill Creek | N/A | Marginal | Marginal | Marginal | Marginal | Marginal |
Lower Waihopai | Marginal | Marginal | Marginal | Marginal | Marginal | Marginal |
Mid Waihopai | N/A | Marginal | Marginal | Marginal | Fair | Marginal |
Ohinemahuta River | Good | Fair | Fair | Fair | Fair | Fair |
Spring Creek | Fair | Fair | Fair | Fair | Fair | Fair |
Lower Wairau | Fair | Fair | Fair | Fair | Fair | Fair |
Are Are Creek | N/A | Marginal | Marginal | Marginal | Fair | Fair |
Tuamarina River | Marginal | Marginal | Marginal | Marginal | Marginal | Marginal |
Wairau Diversion | N/A | Marginal | Poor | Poor | Fair | Marginal |
Lower Ōpaoa | Marginal | Fair | Fair | Marginal | Marginal | Marginal |
Mid Ōpaoa | Marginal | Fair | Marginal | Marginal | Marginal | Fair |
Omaka River | Fair | Fair | Marginal | Marginal | Good | Fair |
Taylor River | Poor | Marginal | Marginal | Marginal | Marginal | Fair |
Murphys Creek | N/A | Marginal | Marginal | Marginal | Fair | Fair |
Doctors Creek | N/A | Marginal | Marginal | Marginal | Marginal | Marginal |
The historic water quality measures in the above table are summarised across all years and for all three sites into the below chart. We can see from the chart that the majority of the WQI measures are either fair or marginal, with a small number of good and poor measures. The latest WQI summary up to 2022 is in the Wairau Current Freshwater State page.
Recreational Water Quality
The recreational water quality programme evaluates the health risk to swimmers at 16 popular swimming location within the region, 8 of which are river sites, through the monitoring of Enterococci and E. coli levels. To assess the risk to water users, the council collects weekly water samples from the most frequented beaches and river sites during the summer months. Measuring the concentrations of all harmful microorganisms, or pathogens, in these samples is both complicated and costly. Instead, samples are analysed for indicator bacteria, which are easier to measure and typically coexist with harmful microorganisms. E. coli serves as the indicator bacteria for river samples. The results are reported each year and provide quality trends over time.
Today, two types of reporting are used for recreational water quality monitoring: NPS-FM 2020 attribute bands and Suitability for Contact Recreation Grades (SFR grades). Prior to the NPS-FM 2020, only SFR grades were used. Determining the SFR Grade for a swimming site is done in two parts. The first part is an assessment of the health risk from all potential faecal sources within the catchment. Based on the assessment, sites are assigned one of five Sanitary Inspection Categories, SICs. The second part of the SFR grading is the Microbiological Assessment Category (MAC). The MAC is calculated from bacteria concentrations in samples taken at a site over a period of five years. You can read more about the process for SFR grades below:
Go to the Recreational Water Quality Reports page
The grades can be summarised as follows:
The map right shows the recreational monitoring sites for the whole region.
To the bottom half of the map are the Wairau FMU monitoring sites, which are:
12. Ohinemahuta River at Onamalutu Domain
13. Wairau River at Ferry Bridge
14. Wairau River at Blenheim Rowing Club (BRC)
15. Taylor River at Riverside
16. Waihopai at Craiglochart
These are all river sites. There are not any coastal sites in this FMU.
Historical SFR grades in this FMU back to the start of the monitoring programme are summarised below:
Historic SFR grades for Wairau FMU river monitoring sites, by summer season | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
Monitoring site | 09/10 | 2010/11 | 2011/12 | 2012/13 | 2013/14 | 2014/15 | 2015/16 | 2016/17 | 2017/18 | 2018/19 |
Ohinemahuta | N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A* |
Wairau at Ferry | Fair | Fair | Fair | Fair | Fair | Fair | Fair | Fair | Fair | Fair |
Wairau at BRC | Fair | Good | Fair | Good | Good | Good | Good | Fair | Fair | Fair |
Waihopai | Poor | Poor | Poor | Fair | Fair | Fair | Poor | Poor | Fair | Fair |
Taylor at Riverside | Very Poor | Very Poor | Very Poor | Very Poor | Very Poor | Very Poor | Very Poor | Very Poor | Very Poor | Very Poor |
The above table and chart show mixed results for SFR grades over the decade. Some results are clear, such as the continued very poor SFR grade for the Taylor River at Riverside. High E. Coli concentrations noted during dry weather conditions from monitoring work at the Taylor River led to the 2013 “Investigation into High E. Coli Concentrations in the Taylor River during Low Flows” report. The report aimed to determine the possible sources of contamination during the low flows and concluded that the main sources were likely wildfowl and dog faeces, though human sewerage contamination was also noted. This report led to an ongoing work programme related to improving overall water quality in the Taylor River.
The Recreational Water Quality Reports available on the council website provide discussion around the historical SFR trends. One clear trend is that rainfall has a direct impact on E. Coli concentrations and therefore the quality of the site for recreational use. Generally, the highest E. Coli readings occur in the days after the highest rainfall events. Accordingly, the ‘unsafe’ concentrations were usually caused by runoff because of rainfall.
More recent SFR grades are discussed in the following current water quality section below.
* Ohinemahuta River site was first monitored at this time but there was insufficient data to derive and report a trend until 2021/2022 summer.
Catchment studies
Where State of the Environment monitoring has shown that water quality is degraded, catchment studies are carried out. These studies provide insight into the causes of poor water quality. Using the information from catchment studies council can work with landowners to address problems and improve water quality. The catchment reports are linked below.
Mill Stream 2009
This catchment study was undertaken over the course of 2008 to investigate the water quality of Mill Stream and to establish ongoing surface water quality monitoring. Prior to the study, the water quality was coming under scrutiny for perceived deterioration and subsequent problems with use.
The study established 15 monthly monitoring sites, which found that water quality was poor in relation to 6 out of 10 parameters measured. Suspended solids, turbidity, E. Coli, and nitrate in particular were of concern. Actions such as removing stock from waterways, riparian planting, stabilising banks and soil, and overall reducing erosion were identified as being required. Land use practises outside of the immediate catchment were also likely having an impact on water quality. A permanent SOE monitoring site was established from this study which continues to be monitored as part of the programme, discussed above.
Are Are Creek 2015
Are Are Creek flows through the Kaituna valley and is a tributary of the Wairau River. Monthly State of the Environment monitoring at the bottom of the catchment has shown that water quality is poor. In order to find the causes, a total of 24 sites located throughout the catchment were sampled on 6 occasions in 2013 and 2014. A number of physical and chemical parameters were measured at each site including E. coli, nutrient concentrations, turbidity, water temperature, pH and Dissolved Oxygen saturation. Parameters exceeded guideline values for the protection of ecological and recreational values at the majority of sites monitored. The site with the worst water quality was located on a small tributary in the mid catchment. Further investigations revealed direct discharge of sewage, together with effluent discharges and silage leachate was causing the deterioration in water quality. Remediation works were initiated and are on-going. At the majority of the other sites direct livestock access and lack of shading by tall bank vegetation were key contributors to poor water quality. Additionally, nitrate leachate from pastoral land use into subsurface flow and groundwater entering Are Are Creek in the mid and lower reaches caused elevated Soluble Inorganic Nitrogen concentrations.
Doctors Creek 2015
Doctors Creek is a tributary of the Taylor River, which flows through central Blenheim. In the 2013 Surface Water Quality - SoE Report, Doctors Creek ranked in the bottom five of the 34 sites monitored. During base-flow, Doctors Creek supplies a significant portion of surface flow to the lower reaches of the Taylor River. The banks of the Taylor River are part of a popular recreational area for walking, running, cycling and rafting. In some areas the river is also used for swimming.
A report was prepared as a result of a substantial investigation into the water quality of Doctors Creek carried out in 2013 and 2014. This was an extensive catchment characterisation of Doctors Creek, combining Hydrological, Geological, Soil and Land use information as well as the monitoring results.
Ground Water Quality
Groundwater quality in the district is measured through three programmes:
- State of the Environment Groundwater Quality Programme, measured quarterly through 23 wells.
- Coastal sentinel wells on the eastern coastline at Rārangi. Five wells sampled over the summertime.
- National pesticide monitoring measured 4 yearly from 20 wells nationally.
The Wairau FMU is home to the largest quantity of groundwater in the district. Ground water is comprised in aquifers, unique to the Wairau area due to the geology and geography of the landscape which permits this type of water movement and retention. There are eight major aquifers on the lower Wairau plains as shown on the map below.
Map of groundwater quality monitoring wells – Wairau FMU in pink
The largest aquifer is the Wairau Aquifer, which underlies most of the northern Wairau Plain. This aquifer does and has received the greatest focus in the region as most of the water used by Blenheim and its hinterland for agricultural irrigation, industrial processing, and municipal and stock supplies are sourced from this aquifer. There are more than 20 other identified aquifers in the FMU. Some of these are riparian aquifers, such as the Are Are Creek gravels and the Waikakaho River gravels, which eventually feed into the Wairau River system. Other aquifers have been identified as being separate to the Wairau Aquifer and include the Benmovern, Brancott, Omaka, Omaka River and Taylor River Aquifers. Towards the coast, there are the Coastal Wairau Plain aquifers, Riverlands, and the Rārangi Shallow Aquifer. Due to the location of these aquifers adjacent to the coast, abstraction of water from these aquifers creates the potential for seawater intrusion and as such is closely monitored – through the sentinel well network discussed below. Many of these aquifers are also the source of water supply for the local communities with domestic water supplied from shallow wells.
State of the Environment groundwater quality monitoring
The quality of groundwater is monitored by the Council through several programmes. Every quarter, State of the Environment sampling is carried out in 23 wells across the area and measures a range of chemical and physical parameters. Some of these sites are also sampled annually for microbes, isotopes and pesticides. Other groundwater systems exist but have no formal name yet, such as those linked to the Rai/Te Hoiere/Pelorus River system and beneath Havelock or Picton.
Unlike the surface water SOE monitoring, the groundwater monitoring is not combined into a single quality measure (like the WQI) which can be compared across the 23 sites. Likewise, some groundwater reporting combines quality and quantity, and separate aquifers from time to time are subject to more intensive monitoring and review rather than a set reporting programme, such as that for surface water.
Further details can be found on the Council’s website for groundwater reports and special investigations pages below:
Location of Rārangi Shallow Aquifer and Coastal Sentinel Wells
Coastal sentinel wells
MDC maintains a network of groundwater monitoring wells along the Rārangi coastline, pictured below.
The main purpose of the monitoring network is to provide early warning of seawater intrusion. The monitoring wells record continuous water level and conductivity data for the Rārangi Shallow Aquifer (RSA). The monitoring occurs every summer.
This work is important for maintaining potable supply for domestic and irrigation needs, particularly in the light of rising sea levels and potential for increased salinity in the wells.
The network has provided important conclusions about the RSA, for example that peak conductivity values in the aquifer are caused by natural leaching of wind-blown sea-salts transported by spring rains. Therefore, the background seasonal variation in salinity in the unconfined aquifer is driven in most seasons by natural processes independent of pumping.
Read more about the sentinel well programme below:
National pesticide monitoring
Every four years, since the early 1990s, the Council has participated in the National Pesticide Survey co-ordinated by the Institute of Environmental Science and Research (ESR). This involves testing 20 sites nationally for 58 herbicides, fungicides, and insecticides. This ongoing study has detected very few pesticides, and all below maximum allowable values in the Drinking Water Standards for NZ (2005/2018). The next round of sampling will be in late 2022 and will including PFAS monitoring. There has also been some monitoring of aquifer invertebrates to characterise the biological communities that inhabit aquifers, but this is still in its infancy.
As part of the 1994 national survey there were 4 wells in Marlborough where pesticides were detected. Several of the wells sampled were near known contaminated sites however. Between 1998 and 2006 the wells surveyed were more representative of general land use and there was a pattern of generally decreasing pesticide levels. For the 2010 and 2014 surveys there were no pesticides detected at any of the wells sampled.
Nationally, there was a slight decrease in pesticide concentration in groundwater between 1990 and 2010. Considering all national surveys, pesticide levels across the country were very low at that time with most concentrations being less than 1% of the maximum allowable value of the drinking water standard.
Water quantity
Surface water quantity
The Wairau FMU has a significant amount of water use for a range of activities including irrigation, private domestic supply, reticulated town supply, industrial processing, and stock water.
The upper mountainous part of the Wairau River has no surface or groundwater takes and is in a highly natural state. Most surface water takes are between the Branch River confluence and the State Highway 6 bridge, as well as the lower reaches of the Waihopai River catchment. Between the Waihopai River confluence and Wratts Road, there are also major losses to groundwater, the consequence of which is low river flows at State Highway 1 in dry seasons.
Two hydroelectric power schemes also affect water quantity in the FMU, located on the Branch and Waihopai Rivers. The Branch Power scheme located on the lower Branch River diverts water from the river and into Lake Argyle, before passing through two power houses. Water then discharges into the Wairau River about seven kilometres from the Branch River confluence. This causes significant variations in the Wairau River flow of up to 20% either side of daily mean flow.
Surface water quantity is measured through river flow rates (m3/sec) which are measured continuously. In the Wairau FMU, this has been measured at a number of locations across various lengths of time. The main sites are summarised in the table below.
Wairau 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 |
Wairau River | 3,430 km² | 100 m3/sec | 8 m3/sec | 1,700 m3/sec | 2.25 m3/sec | 2,921 m3/sec |
Branch River | 551 km² | 19.62 m3/sec | 3.01 m3/sec | 428.98 m3/sec | 2.49 m3/sec | 925.35 m3/sec |
Omaka River | 91 km² | 1.14 m3/sec | 0.15 m3/sec | 40 m3/sec | 0.07 m3/sec | 253 m3/sec |
Taylor River | 65 km² | 0.69 m3/sec | 0.04 m3/sec | 45 m3/sec | 0.01 m3/sec | 197 m3/sec |
The mean flow at the Wairau River, Tuamarina site is 100 m³/sec, which is a mean over the entire time the site has been measured. Comparison of the mean flows in the above table highlight the significantly larger volume of water in the Wairau, further supported by comparison with other waterways regionally, such as the Rai River (Te Hoiere/Pelorus) at 11.4 m³/sec or the Awatere at 14 m³/sec.
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.
Ground water quantity
Most of the water used on the lower Wairau Plains area is taken from the multiple aquifers in the region and primarily the Wairau Aquifer. Council maintains 30 wells as part of Council’s groundwater quantity network which record aquifer levels, water temperature and electrical conductivity for some wells near the coast.
Abstraction of water in the region is strictly controlled through pMEP rules. Small water takes for domestic and other uses are permitted activities as long as they do not exceed certain volumes in a particular period and meet applicable standards defined in the pMEP. Council consents are required for greater quantities, and there are detailed rules relating to specific aquifers for allocation volumes, flows and levels which must be maintained. These controls and rules have been in place for around 30 years and have assisted to prevent over allocation of most of the aquifers. As further science is undertaken, our knowledge and understanding of these aquifers continues to increase and, in the future, this may result in changes to allocation regimes.
Groundwater quantity SOE well network
Groundwater quantity is measured through the State of the Environment programme, using a well network across the lower plains developed for this use. Some wells in the programme have been monitored for over 50 years but the SOE groundwater quantity has been reported since 2010. The map right shows the Wairau Plain and Lower Wairau Valley including the location of these monitoring sites labelled with their MDC identification number. The groundwater quality monitoring network is more extensive.
The groundwater quantity report purpose is to review the effect of both permitted and consented groundwater use during the previous summer season, and to describe the state of the main aquifer systems leading into the next summer, the time of highest water demand. It is effectively the natural resource equivalent of a set of accounts or in other words a water budget for the coming season, and the balance for the previous summer season.
The earliest records for aquifers and trends prior to 2010 are summarised in the first report, released that year. The Wairau aquifer is summarised below; the balance can be viewed in the report itself (link below). More current trends to 2023 are discussed in the following sections.
