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December 2016
TANK newsletter/ panui on the collaborative group developing a Regional Plan to manage land and water in the Tutaekuri, Ahuriri, Ngaruroro and Karamu catchments - TANK.
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Think TANK VI

Meeting 25                                                                                         
The TANK Group navigated an agenda packed with findings from HBRC’s science team and well-informed Group discussion. Beginning with the Karamū catchment and options to manage its water quality, talk then shifted to a demonstration of HBRC’s new Surface-Groundwater model for the Heretaunga system, ending with water allocation scenarios for the Tutaekurī and Ngaruroro Rivers - it was a full meeting.

The Group started by voicing appreciation for being able to see the Ngaruroro River first-hand on the 20 November jet boat trip – many thanks to the organisers for a unique day.      
 

KARAMŪ | water quality - ecology
The Group looked first at Karamū Stream ecosystem needs, then the flood management and drainage values that this catchment caters for.
“In the Karamū catchment we’ve got the poorest quality health in any of TANK’s catchment areas – waterways that are effectively drains. So do we or should we treat different ‘waterways’ differently?”
- Bruce Mackay
“Even drains are waterways. They hold water that needs to be managed for water quality and ecology. All water in a natural state must be managed outside of a pipe, drain or cistern.”
- Mary-Anne Baker
The Group had different views of drains and streams, looking for some definition to help future decision-making. In some places streams are natural waterways; in others modified water-courses draining water from productive land. Streams either convey water through a location, or drain water from it noting that many landowners have, over time, created new drains or streams to carry water. The Group discussed that where water flow is present, it must be managed for an acceptable level of water quality.  

HBRC Scientist Sandy Haidekker outlined the lack of various sensitive bugs and insects in the Karamū catchment - indicating poor ecosystem health. This is due to many inter-dependent factors putting stress on the water environment: low levels of dissolved oxygen, high summer water temperatures, poor habitat, elevated nutrient levels, prolific aquatic weed growth, low flows and water volume. These all create habitat which is unsuitable for aquatic life to survive and thrive.
  Te Waikaha Stream at Mutiny Road has good health                                     Awanui Stream at Turamoe Road has poor health


Nutrients generally enter waterways as a ‘non-point source’, as runoff from land or leaching via groundwater, but tile drains can be a ‘point source’ for nitrogen in rain events. Another point source of contaminants comes from stormwater runoff - especially the urban areas of Havelock North and Hastings. Streams in Karamū catchment have typically little shade or streamside planting.

The main factors affecting ecological health are low dissolved oxygen and high temperature.  Dissolved oxygen is especially affected by nuisance aquatic plant growth.  Both temperature and oxygen levels can be improved by streamside planting – offering shade to reduce weed growth.  Other management options to control plant growth include using targeted herbicides, the potential for grass carp introduction, dredging or increasing the flow to remove macrophytes and possibly the management of nutrients. Appropriate streamside planting will reduce water temperature, reduce nuisance plant growth, help to retain oxygen and better support a habitable aquatic environment.

The science is not clear about how much effect nutrient management will have. Current evidence points to riparian shading as being the best management approach.  However, nutrient inputs into the estuary must be considered and any moves to reduce nutrients in the Karamū catchment will be of benefit to the wetlands at Waitangi Regional Park and the coastal environment beyond.
KARAMŪ | minimum flows
“Other ways to protect fish, etc. than just minimum flows… Riparian planting and other measures may improve aquatic habitat in some waterways better than increasing minimum flows.”    TANK Group, May 2013

HBRC Scientist Thomas Wilding summarised how TANK Group decision-making would need to have considered the relationship between minimum flows and setting limits for oxygen in streams.

Physical limitations in low-gradient streams such as the Awanui, Irongate, Karamu, Karewarewa and Raupare could affect the ability to improve oxygen levels, i.e. there is simply not enough flow to begin with in these streams. That aside, the Group will still have to consider an appropriate dissolved oxygen objective.

While there are some native fish in streams, i.e. Raupare and Awanui, oxygen levels could be improved to better support native fish populations in the Karamū catchment.  Higher concentrations of oxygen - above what fish would need - may be required to provide the right conditions for bug and insect communities.
Dissolved oxygen levels are linked with flow and also affected by seasonal plant growth. Oxygen is more critical for the Karamū than water depth and flow. Comparatively, in the wider, gravel-bottomed Ngaruroro and Tutaekurī Rivers, water is constantly being aerated.   
Riparian ‘streamside’ shading (as above) is also recommended by water ecologists as a viable way to improve Karamū’s ecosystem. More shade means less weed and around 10-15% more oxygen supply and less demand from fish due to reduced water temperature.
KARAMŪ | drainage and flood management
“It is really valuable that we keep and hold water in the landscape. Need to think about how we drain and retain water in our land. Holding water up in the catchment solves a lot of problems downstream.” - Gary Clode

HBRC Engineer Gary Clode presented on drainage and flood control.

Karamū Stream and its tributaries are part of the Heretaunga Plains Flood Control Scheme (HPFCS), protecting people and property from floods and draining land to enable crop and food production. HPFCS services 138,000 (86%) of the region’s population, including the urban areas of Clive, Havelock North and Hastings.

The ‘old-days’ approach to flooding and drainage has given us a waterway network designed primarily for the efficient movement of water. Flooding in 1867 resulted in the original course of the Ngaruroro River shifting away from what is now the Karamū Stream in Havelock North. In 1934, the region’s Catchment Board started work on HPFCS, and further redirected the course of the Ngaruroro away from Clive River in 1969 to prevent future flooding in Clive.  If the TANK Group value ecosystem objectives above flood management, vegetation that creates shading may also reduce floodwater-carrying capacity. 

The Karamu drainage scheme includes 210km of waterways directly managed by HBRC and five Havelock streams managed by Hastings District Council. The remaining drainage network sits on private land. Works Group maintenance carried out by HBRC ensures the drainage network functions as expected. Key issues for the Council in administering the drainage scheme are maintenance access and riparian land management across private land, erosion and slumping, excessive weed growth and maintaining agreed levels of service relating to the drainage and flooding network.

HBRC has already recognised that the community seek for Karamū waterways to meet a wider set of management objectives than just flood and drainage management.  As of 2007, HPFCS included the Karamū Stream Enhancement Project to increase biodiversity with mainly native revegetation, over 30 km from Pakipaki to Clive. Community, marae, church and environmental groups, schools and some landowners adjacent to Karamū Stream have contributed to this enhancement work.

Biodiversity, flood and drainage objectives must now be considered along with management objectives for aquatic ecosystem values.  In most cases these objectives align with each other.  However, in some waterways, flood management requirements might influence options for riparian land management.
KARAMŪ – recommendations and next steps
In summary, the primary attributes for managing Karamū water quality are: dissolved oxygen, temperature and flow. The objectives the TANK Group wants to manage for are:
  • improve bug and insect life (macroinvertebrates, over the long term), and
  • improve values for fish (over the period of a 10 year/ Long Term Plan).
To meet these objectives, the Group will focus on improving dissolved oxygen and reducing temperatures using a riparian land management programme to increase shading of the water.

As a result of this meeting, Regional Council staff will:
  • develop options/ priorities for planting and stream redesign on public land and private land
  • report back on flow management
  • provide opportunity for more discussion and information on nutrient management particularly relating to their impact on estuary values
  • consider management opportunities in Pekapeka and Lake Poukawa wetlands to help manage water quality in the Karamu catchment.
HERETAUNGA | modelling to support TANK decision making
The Council has been working with experts to develop a comprehensive ground and surface water model. The model will help to understand how different water management approaches might affect the Heretaunga Plains and the Ngaruroro, Karamu and Tutaekuri rivers.  The TANK Group received a presentation from the modelling team to explain how the model was built, some detail about the groundwater component and how the model was calibrated. The team also demonstrated how closely the model results imitated already-measured data, comparing the model against actual spring flows and seasonal variation in groundwater levels.

Some preliminary results illustrated stream flow depletions and aquifer drawdown using current water use and also showing the result if maximum allocations were abstracted.  There was a draw down across the plains of about 1-2 metres using current abstraction compared with about a 5-metre drawdown using the maximum allocated amount.  The long term impact on groundwater levels under current abstraction appears to be stable, i.e. no declining trend in the long term. More analysis of the impact of water abstraction patterns on spring and river flows is needed.  The next step in developing the model is to better understand the groundwater takes that have an effect on stream flows.

Like all models, there are some uncertainties and limitations, such as confirming its reliability – where water meter data has not always been reliable, uncertainty about future climate change, limitations relating to scale and resolution.  However, the modelling team are confident in the model’s ability to predict changes in groundwater levels and river flows using different water management scenarios.

The MODFLOW and SOURCE computer programmes that make up the Heretaunga Plains model contain hundreds of model parameters and thousands of observations (data points).  This level of data complexity has required the processing power of Auckland University’s supercomputer. One instance of running a model scenario used 50,000 computer hours, comparable to 6 years of computing on one PC.

“It is significant to see the level of expertise that been brought to the table, the monitoring data that is being generated and the time being dedicated to delivering reliable and usable information.”
- Vaughan Cooper

“We need to know specifics of the timing of the water ban shutoffs, due to the effect on crops at times during January and February.”
- Ivan Knauf


HERETAUNGA | how to use the model
With the model now in place, it can be used to predict changes in the river and groundwater flows according to different management decisions.  The Group will develop different management scenarios. Staff will then use the surface/groundwater model to see what happens to river and spring flows and security of supply under different water use scenarios.
This might include:
  • staged reductions - users gradually reducing how much water they use
  • a ban on water takes – all users cease all takes
  • flow-sharing regimes – decreasing water use proportionally with decreasing river flows.
The group will pick minimum flow regimes according to different levels of protection for the ecosystem.
Again, it was a full meeting. Fortunately there will be a review of much of this work early in 2017 and a chance to consolidate the Group’s findings and discussions to date.

See www.hbrc.govt.nz, search #tankresources for more details.
Please pass this newsletter/ panui on to anyone you think might benefit from it.
Got any comments or questions about this newsletter? Email Mary-Anne Baker
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