Current Freshwater State
Water quality
Current SOE monitoring – NPS-FM attribute measures
The MDC surface water quality monitoring network was updated in 2020 to better align with the requirements of the NPS-FM. Where possible, this included having one river water quality site per FMU for efficiency and clarity purposes. For the Te Hoiere/Pelorus FMU, this is the “Rai River at Rai Falls” site, which has been monitored in various capacities since 1979.
The below tables detail the most recent results from the 2020 and 2023 State of the Environment Reports for seven surface water attributes currently monitored and their results in terms of NPS-FM classification. This classification is in ‘bands’ from A-E, which the A-band representing healthy ecosystems, while attribute states in the D and E bands are considered ‘below the national bottom line’. Unless caused by natural sources, attributes below the national bottom line are considered unacceptable.
Te Hoiere/Pelorus NPSFM monitoring results, State of the Environment Report 2020 | |||||||
|---|---|---|---|---|---|---|---|
River | Periphyton | Ammonia | Nitrate | E-Coli | MCI1 | APSM2 | DRP3 |
Ronga | A | A | A | B | C | B | B |
Opouri | B | A | A | A | B | B | B |
Rai | N/A | A | A | A | C | B | A |
Upper Pelorus | N/A | A | A | A | B | B | A |
Lower Pelorus | N/A | A | A | A | C | C | A |
Wakamarina | N/A | A | A | A | B | B | B |
Kaituna | B | A | A | B | C | B | B |
Te Hoiere/Pelorus NPSFM monitoring results, State of the Environment Report 2023 | |||||||
|---|---|---|---|---|---|---|---|
River | Periphyton | Ammonia | Nitrate | E-Coli | MCI* | APSM** | DRP*** |
Ronga | B | A | A | D | B | B | B |
Opouri | N/A | A | A | C | B | B | B |
Rai | C | A | A | D | C | B | B |
Upper Pelorus | N/A | A | A | A | B | B | A |
Lower Pelorus | N/A | A | A | B | C | B | A |
Wakamarina | N/A | A | A | A | B | B | B |
Kaituna | B | A | A | D | C | B | B |
* Macroinvertebrate Community Index – NPS-FM State 1
** Macroinvertebrate Average Score Per Metric – NPS-FM State 2
*** Dissolved Reactive Phosphorus
The NPSFM attributes from both the 2020 and 2023 reports show generally good results for the Te Hoiere/Pelorus FMU. The key change noted is a decline in E. Coli attributes from only A or B band scores at the 2020 report to much more varied results at 2023, including D band results. This is further discussed below. Most of the other attributes are more stable, with limited band movement. The other key change is the Periphyton attribute, which has declined overall to B/C bands rather than A/B bands.
The Te Hoiere Project is aiming to improve overall river health in the catchment which will subsequently also result in lower E. coli concentrations. E. coli concentrations in natural conditions are typically low, with occasional spikes observed during rainfall runoff events. Comparatively low E. coli levels are noted in several waterways including the Upper Te Hoiere/Pelorus River. At most sites regionally, the highest E. coli concentrations are generally associated with rainfall. Streams in high rainfall areas in the north of the region experience more surface runoff events, resulting in consequently lower NPS-FM states. Significant rainfall events occurred over the time of the data set used for the 2023 report, which was 2018-2022.
At the 2020 report, the poorest NPS-FM attribute in this FMU was the Macroinvertebrate Community Index (MCI). This is an important measure of overall stream health. Macroinvertebrates are aquatic insects and other soft-bodied animals that can be seen with the naked eye. Some sensitive species will not be present in streams with degraded water quality. A pollution index has been developed based on the number of macroinvertebrates from different species found in a sample. This index is the ‘MCI’. The higher the MCI score, the better the water quality. We can see there are C band MCI results. These are generally in rivers with catchment areas that have more intensive farm uses than the A band catchment areas. Accordingly, the C band sites are a focus of the Te Hoiere/Pelorus project.
Current SOE monitoring – Water Quality Index
As discussed above, the monitoring network measures nine State of the Environment surface water quality parameters to form the Water Quality Index for each site. The most recent two years’ reporting is shown below:
Te Hoiere/Pelorus SOE monitoring sites – current WQI measures | |||
|---|---|---|---|
Monitoring site | WQI 2018-2020 | WQI 2019-2021 | WQI 2020-2022 |
Ronga | Marginal | Marginal | Marginal |
Opouri | Marginal | Marginal | Fair |
Rai | Marginal | Marginal | Fair |
Upper Pelorus | Fair | Fair | Fair |
Lower Pelorus | Fair | Fair | Fair |
Wakamarina | Good | Fair | Fair |
Kaituna | Fair | Marginal | Fair |
The WQI indexes in this area are mainly marginal or fair, which leaves room for improvement in this FMU. The parameters contributing to these indexes are more varied in this FMU compared to other areas. E. Coli and Dissolved Inorganic Nitrogen (DIN) had a greater contribution than other parameters. E. Coli is discussed more thoroughly in the Recreational Water Quality section; DIN is discussed in more detail below.
There was a decline in one waterway with the Wakamarina River moving from ‘Good’ to ‘Fair’. This was due to an increase in dissolved nitrogen concentrations, which was a trend noted in other FMU waterways. Most of these nitrogen increases were caused by the higher-than-average rainfall experienced over the year, which resulted in greater leaching losses. Although the WQI moved down a grade, the reduction was numerically minor as previously the Wakamarina River had only ‘just’ qualified for a ‘Good’ grade.
Nitrate, Ammoniacal nitrogen and Nitrite are soluble forms of nitrogen that are easily taken up by plants. They are collectively referred to as ‘Dissolved Inorganic Nitrogen’, abbreviated as DIN. High DIN concentrations can cause excessive growth of aquatic plants such as algae. This is not only visually unpleasing, but the algae smother available habitat for many aquatic insects, which in turn are a food source for fish. This can cause a significant reduction in biodiversity. Naturally, DIN concentrations are low. This can be seen in catchments that remain almost entirely covered in native vegetation, such as the Upper Te Hoiere/Pelorus River.
Cattle urine is one of the main sources of nitrogen leaching. It is therefore not surprising that some of the dairy catchments have generally higher DIN concentrations. The highest values are observed in the Ronga, Rai and Kaituna rivers in this FMU. The ongoing work by landowners and the wider community through the Te Hoiere/Pelorus project to reduce nitrogen leaching is crucial work in this FMU for improved water quality. It is noted however that the NPS-FM attributes for Nitrate discussed below are A band for this area.
Recreational water quality monitoring
The three recreational water quality monitoring sites in this FMU produce results at opposite ends of the spectrum in the most recent 2022/2023 report, in line with previous years. As has been observed in previous seasons, the lowest E. coli concentrations were measured at the Pelorus Bridge, while the Rai Falls registered the highest bacteria levels. The elevated E. coli concentrations in the Rai River result in higher levels at Totara Flat, located downstream of the confluence of the Te Hoiere/Pelorus and Rai Rivers.
The Suitability for Recreation Grade (SFR) for the Te Hoiere/Pelorus River at Pelorus Bridge has remained 'Good' for a decade, making it the river site with the region's best recreational water quality. In contrast, Totara Flat and Rai Falls each hold an SFR Grade of 'Poor'. Trend analysis reveals little change in E. coli concentrations at the two Te Hoiere/Pelorus River sites, but a noticeable increase at Rai Falls over the last 10 years.
Similarly, the 2021/2022 report states that the Pelorus River site at the Pelorus Bridge has the best water quality of all the sites monitored and an NPS-FM state of “Good”. In contrast, downstream in the same river at Totara Flat, the NPS-FM state is “Poor”. Unfortunately, the third site on the Rai River at Rai Falls had not been re-operational for long enough to provide sufficient data for a grading. However, the testing indicated that the site will most likely be graded “Poor” too, due to the site having the poorest water quality samples of all eight sites across 2021/2022.
NPS-FM states of E. Coli concentrations for river monitoring sites, by summer season | |||
|---|---|---|---|
Monitoring site | 2020/2021 | 2021/2022 | 2022/2023 |
Rai River at Rai Falls | Insufficient data | Insufficient data | Poor |
Te Hoiere/Pelorus at Pelorus Bridge | Good | Good | Good |
Te Hoiere/Pelorus at Totara Flat | Poor | Poor | Poor |
Groundwater quality
There is one groundwater quality monitoring well at “10323 Rai Valley” in this FMU. The five-year median monitoring result is shown below:
Rai Valley Groundwater quality monitoring site #10323 | ||
Quality indicators | 5-year median | Comment |
Chloride | 8.5mg/L | Concentrations are overall increasing. |
Dissolved reactive phosphorus (DRP) | 0.01mg/L | Concentrations are overall falling, a gradual trend. |
Electrical conductivity | 151µS/cm | A measure which reflects the dissolved salt content (natural and human derived) and therefore how dilute the water is. Groundwater at this well has a significant range in values over time. |
Nitrate nitrogen | 4.6mg/L | Long term levels are within human health threshold but relatively high in ecological terms. |
Records at the monitoring well so far record the following information and trends to April 2023:
- The annual seasonal variation in stage (level of water in the well) is normally 1 metre but can be up to 1.5 metres in some years.
- Interestingly, there were virtually no E. Coli microbes present in the groundwater at this well despite an underlying intensive land use and high E. Coli at the Rai Falls surface water monitoring site.
- High magnesium and iron concentrations in the groundwater at this well compared to the rest of the SOE groundwater monitoring network are in part due to the mineral belt which naturally occurs in the western side of the catchment.
Municipal supply
The most significant urban water use is Havelock municipal water supply. This is a reticulated, council owned scheme servicing residential properties in the township. It is supplied from two bores adjacent to the Kaituna River. Chlorine is added to the water at the pump station, then the water is pumped to a new steel service reservoir, built in 2010.
Water quantity and use
In June 2023, the Te Hoiere/Pelorus FMU rivers (Rai, Pelorus, and Kaituna) all had mean flows around 50% of their long-term means. This was predominantly due to low rainfall during the month. All three rivers have significant flow records dating back to the 1970s-80s, so their long term mean flows are well established.
Individual Resource Consents
Generally, this FMU is considerably less irrigated than the Wairau plain and is predominantly dairy farm platform irrigation and accordingly a lower quantity of water is used for this purpose. There are considerably fewer water take resource consents than the Awatere or Wairau FMU despite the larger amount of surface water available.
The number of water take Resource Consents (RC) in this FMU are shown in the table below. An additional 5 water take RCs exist in the Wakamarina area which is not included on the Appendix 6 allocation table. The numbers are correct as at October 2023.
Quantity allocations for water takes | ||||
|---|---|---|---|---|
| Go to Appendix 6 Schedule 3 pMEP | ||||
Freshwater management unit | Class | Allocation Cubic metres/day | Allocation Cubic metres/year | No. of take Resource Consents |
Kaituna | Municipal Supply A B | 2,000 83,250 219,790 | N/A N/A N/A | 7 (aggregated) |
Opouri | A B | 10,195 17,280 | N/A N/A | 4 (aggregated) |
Pelorus – Lower | A B | 45,000 45,000 | N/A | 14 (aggregated) |
Pelorus – Upper | N/A | 0 | N/A | 0 |
Rai | A B | 29,635 60,480 | N/A | 17 (aggregated) |
Ronga | A B | 4,665 8,640 | N/A | 3 (aggregated) |
Tunakino | A B | 4,752 8,640 | N/A | 1 (aggregated) |
With the lack of significant groundwater aquifers in Te Hoiere/Pelorus, water abstractions come directly from rivers or shallow wells and infiltration galleries alongside the river. Water takes are controlled by MDC and daily allocation limits placed on municipal water supplies as well as other takes. Where allocations are not specified, controls are placed on takes relating to the river’s mean flow levels. There are also cut off levels for different classes of takes. This is shown in the table below.
As discussed above, irrigation water is classed with different rationing and cut off flows for each class. C class is taken for placing into water storage, generally during periods of high flow – as shown by the higher rationing and restriction flow cut offs. When the flow levels are recorded as falling below the rationing or restriction amounts, associated steps are taken by water users to comply with this management.
Minimum flows and levels for water takes | ||||
|---|---|---|---|---|
| Go to Appendix 6 Schedule 3 pMEP | ||||
Freshwater Management Unit | Class | Minimum flow or level (purpose) | Monitoring site | Management flow or level (method) |
Kaituna | A | Minimum of 0.275m3/s at outlet to sea | Reader’s Road Bridge | Fully restricted below 0.275m3/s |
B | Fully restricted below 0.4m3/s | |||
Opouri | A | Minimum of 1.0m3/s at Rai River | Rai River at Rai Falls | Fully restricted below 1.0m3/s |
B | Fully restricted below 1.25m3/s | |||
Rai (total including Opouri, Tunakino and Ronga) | A | Minimum of 1.0m3/s at Rai River | Rai River at Rai Falls | Fully restricted below 1.0m3/s |
B | Fully restricted below 1.50m3/s | |||
Pelorus including tributaries (excluding Rai) | A | Minimum of 3.75 m3/s at Fishermans Flat | Totara Flat | Rationed below 3.15 m3/s Fully restricted below 2.69 m3/s |
B | Rationed below 3.6 m3/s Fully restricted below 3.2 m3/s | |||
Ronga | A | Minimum of 1.0m3/s at Rai River | Rai River at Rai Falls | Fully restricted below 1.0m3/s |
B | Fully restricted below 1.25m3/s | |||
Te Hoiere Restoration Project
Within the Te Hoiere/Pelorus FMU, the Te Hoiere catchment has been identified as an exemplar catchment as part of the Ministry for the Environment’s At Risk Catchments’ programme and by the Department of Conservation (DOC) as one of its Ngā Awa rivers. This project seeks to bring people together to carry out landscape-scale restorative actions to increase catchment health and put measures in place to prevent further degradation. You can discover more about the project below:
