James Palmer: Beneath the surface of our water debate

James Palmer

Right now there's a great deal of interest in Heretaunga's water resources. These resources are the lifeblood of our region. They need our care and attention.

Some of us think of the Heretaunga Plains aquifer as one big underground lake, or bucket, that we draw from.

But the 'aquifer' is really a network of underground rivers moving slowly along ancient gravel riverbeds. As far as aquifers go Heretaunga is quite fast moving, water travelling more than 100 metres a day in places.

Our challenge is that this underground river network is intimately connected with the rivers and streams above ground. In places, positive pressure pushes water up to springs that add to streams, such as the Karamū and Raupare.

In other areas our rivers and streams lose water to the gravels below - most significantly in Ngaruroro River, which loses around 5000 litres every second.

Over time we have been taking more and more water from this system for our use. Today there are 1780 consented bores drawing about 80-90 million cubic metres of water annually from beneath the Heretaunga Plains.

Industrial demand for water in Hawke's Bay was significant 30 to 40 years ago, but relatively static this century. Town water supplies have been fairly static for 40 years, but irrigation demand has grown at around 10 million cubic metres per decade for the last 30 years.

Because the water above and below ground is connected, the overall impact during hot Hawke's Bay summers is low stream flows, less oxygen for fish, high water temperatures and contaminant concentrations, all harming aquatic life.

To be clear, we're not running out of water. An estimated 3.4 billion cubic metres flows into and through the Heretaunga aquifer each year. About 5 per cent of this is consented for use, with about half of that actually taken.

The challenge we all share is the sensitivity of our bucket to change - most acutely in summer when water demand is highest. While there is a lot more water allocated than used, there is a natural limit to what land people hold and what they can grow.

The council has signalled that future allocation for existing users is likely to be based on historic use.

Until very recently we haven't had the supporting science to tell us exactly what effect groundwater use is having on surface water supply and water quality. With a big investment by ratepayers in the council's state-of-the-art Heretaunga Plains Groundwater Model, we now know just how inter-connected this surface and groundwater is.

Every drop of water we take below ground takes away some water from the environment above ground.

The regional council has been reviewing water rules for the Heretaunga Plains with the collaborative TANK Group (Tutaekuri, Ahuriri, Ngaruroro and Karamū). The council has spent over $3 million on TANK science over the last three years and this is now informing the group's decisions. The TANK Group recently agreed that the effects of water takes on our lowland streams and rivers are at their limit, and no further degradation must occur.

While the TANK Group develops future rules for water use, including a priority for water uses, it hasunanimously supported the council in putting a halt on further Heretaunga water allocation.

In fairness to recent investment decisions relying on water to be available, the council will still process consent applications with evidence that investment decisions were made on the basis of availability of water.

Given recent developments some people have asked why the regional council is not supporting a Water Conservation Order on the Ngaruroro and Clive rivers. We believe the TANK Group process should have a chance to finish its work, given the enormous ratepayer and community investment to date, and the preference for local, community-led decision-making.

We also believe a Water Conservation Order is not the appropriate tool to manage a highly modified catchment. It is inflexible, doesn't account for all values and uses, and does not enable the integrated management of land and water. Water Conservation Orders are best at protecting mostly unmodified lakes and rivers, like Mohaka River, not those that supply a large population and underpin a regional economy.

As summer approaches regional council staff and our community partners are working hard to apply the science to consents management, policy and planning, and to promote water-use efficiency with all users.

Now that we know every drop of water we use in summer takes water away from our streams and rivers, we know we're all in this together and all part of the solution.

James Palmer is the Chief Executive of the Hawke's Bay Regional Council.
All opinions are the writer's and not those of Hawke's Bay Today.