skip to main content skip to main menu
Scroll

News
~ Ngā pānui

news

Making sense of Ngaruroro River science

TANK Group members today heard the latest science from Regional Council hydrologists about flow statistics for the Ngaruroro River, and it contained some surprises.

TANK is the name of a collaborative process being used to draft a Plan Change for catchments including Tutaekuri river, Ahuriri estuary, Ngaruroro river and Karamū stream.

Today’s science on river flows, plus new modelling about how ground and surface water abstraction affect the Ngaruroro River, will help decision-making about managing water in the TANK catchments.

Developing the Heretaunga Plains ground and surface water model included a data review to calculate flow statistics called Mean Annual Low Flow or MALF.  MALF is an average of the low flows observed in a river each year.  This information helps decide how to manage abstractions that affect river flows while protecting fishery and aquatic ecosystem health.  MALF is often used as a basis for informing the management of flow regimes, allocation limits and restrictions on abstraction. 

The TANK Group also learned in February that groundwater resources over the whole Heretaunga Plains are more closely linked than previously thought, meaning the previous approach to stream-depleting takes is likely to change substantially. 

To calculate MALF, abstractions of surface water and the stream depletion effects of ground water takes are added back into flow measurements so that the MALF reflects a natural or ‘naturalised’ flow. 

In working out the new MALF, the modelling team included new data from a groundwater recharge scheme that operated from the 1980s to early-2000s near Fernhill.  The most recent modelling is much more accurate as it includes the flow record from the recharge scheme and updated information about the effects of surfacewater-depleting groundwater takes.

This works shows that the MALF figure is higher than earlier science indicated and has risen from 4,500 to 4,700 litres per second at Fernhill.   This new flow with information about groundwater inter-connectivity will have significant implications for the flow management decision-making for Ngaruroro River and groundwater in the adjacent Plains.  However, the details are still to come as further modelling is carried out. When complete, the TANK Group will consider the impact of various flow and abstraction regimes.

The current restriction regime for irrigation takes includes a ban on water takes when Ngaruroro River flow reaches 2400 litres per second. New water management provisions for the Heretaunga Plains are likely to look substantially different. 

The TANK Group still has difficult technical details to consider before making its final recommendations, anticipated to be later this year. 

More information on the TANK project is at www.hbrc.govt.nz, search: #tank.

17 March 2017

Back to Latest News

843 page views for the last 30 days

Share with a friend  

Disclaimers and Copyright
While every endeavour has been taken by the Hawke's Bay Regional Council to ensure that the information on this website is accurate and up to date, Hawke's Bay Regional Council shall not be liable for any loss suffered through the use, directly or indirectly, of information on this website. Information contained has been assembled in good faith. Some of the information available in this site is from the New Zealand Public domain and supplied by relevant government agencies. Hawke's Bay Regional Council cannot accept any liability for its accuracy or content. Portions of the Hawke's Bay Regional Council information and material on this site, including data, pages, documents, online graphics and images are protected by copyright, unless specifically notified to the contrary. Externally sourced information or material is copyright to the respective provider.

© Hawke's Bay Regional Council - www.hbrc.govt.nz / +64 6 835 9200 / Fax: +64 6 835 3601