7 October 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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The TANK Group focused on sediment on 20 September (meeting 23), discussing different ways to reduce sediment and erosion in lower parts of the Tutaekurī and Ngaruroro rivers, and in some tributaries. Sediment getting into main rivers is likely to be affecting bug and insect levels – which is a measure of river health.

A presentation on the Waitangi estuary showed the general state of the estuary environment.While the council doesn’t have a long record of science data for this estuary, scientists have compared the estuary state with national data and also the state and trends of other estuaries in Hawke’s Bay. Fine sediment build-up in Waitangi Estuary shows negative trends that are affecting ecosystem health. A measure of this is fewer bugs and insects in the water over time. There are concerns that a high rate of sediment is going to the coast with resulting effects on marine life, but the council has very little data to help understand this.

A frequently asked question is “isn’t erosion a natural process?”  The answer of course, is yes, but we also need to understand the difference between what is natural, what is accelerated as a result of land uses, and what that might mean for our freshwater ecosystems.

The natural environment can cope with a certain amount of sediment, but not if the rate of soil loss or deposit is too high.  This shows up in environmental monitoring as reduced MCI (bug and insect) scores and high rates of mud accumulation in the estuary. 

The other effect of accelerated erosion is loss of production for landowners.  When valuable topsoil is lost, there’s less opportunity for pasture growth. Erosion, particularly slips, can also damage roads and tracks. It can result in stock losses and cover productive flat pastures.
Council has carried out Sed-Net (sediment network) modelling of TANK catchments to identify areas most likely at high risk of sediment loss, including streambank erosion. SedNet predicts annual sediment losses and gives an idea where the most sediment is likely to come from in a catchment. 

Sediment yield by sub-catchment.  (Negative numbers indicate sediment accumulation)

SedNet will help TANK Group to:
  • Identify sediment sources
  • Calculate the areas of land vulnerable to sediment generation, and how much comes from these
  • Calculate how much comes from catchments, sub catchments and even farms
  • Predict sediment particle size, and
  • Predict what happens when stock are excluded.
Erosion types and their contribution to total predicted sediment loss

The SedNet model shows the effect of excluding stock from stream banks. If stock were excluded from the whole catchment, sediment loss could reduce by 77% of the total generated from stream-bank erosion.   

The Group asked for more information about sediment sources, possible mitigation measures and their effectiveness at reducing erosion.

The TANK group also heard that reducing sediment can reduce dissolved inorganic phosphorus (DIP) because phosphorus binds to sediment. Though some parts of the catchment have naturally higher levels of phosphorous due to underlying geology. 

There were questions about the SedNet model’s accuracy and usefulness, its calibration and whether it has been used elsewhere. That said, SedNet will help decision-making, allowing comparisons between different management methods.
TANK Member Profile:
Vaughan Cooper
Forest and Bird

Water quality and river flows have been a focus for the organisation I represent - the Forest & Bird Protection Society. For the last 6 years I have been involved in HBRC Plan changes (Regional Policy Statement and Tukituki plus the Board of Inquiry). These Plan Change processes have been combative, time-consuming and not always well supported. The TANK process - using a more collaborative way of working - should produce a better result because of the significant number of vitally interested parties involved.
Besides representing Forest & Bird on TANK etc., I have owned and operated businesses in the primary sector areas of livestock farming, vineyard and mixed orchard. I’ve also been a Management and Technical consultant and learnt to attend long meetings listening to others’ point of view. 
Mana Whenua Working Group
There was great interest from TANK Group members in the working group’s delivery of Mana Whenua values and attributes for the Ngaruroro River.
A comprehensive presentation explained the Te Ao Māori world view to incorporate the Resource Management Act. The working group introduced the five values of Uu, Waimāori, Mauri, Kaitiakitanga, and Whakapapa/ Ki Uta, Ki Tai. An abridged presentation is available online. Finally, a waananga (workshop) was offered to TANK Group members to help communicate more fully the Mana Whenua values-based perspective and further explore how his might be incorporated into the TANK process.
More Info
The TANK Group also considered ways to encourage wider community involvement in this water and land management work.  They voiced a need to share more of the information being considered as part of this plan change process, to also gain wider buy-in to the decisions they make.

As a result, TANK meeting notes will now be publicly available alongside presentations made to each meeting.  See the, search: #tankresources for more details.
NOTE: we want profiles for each newsletter - email a brief bio and photo to to help us show the varied perspectives of TANK Group. 
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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