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Manawatu-Wanganui region

Groundwater Zone: Rangitikei Groundwater MZ

Extending from the hill country of the southern Kaimanawa Ranges to coastal dunes bounding the Tasman Sea, the Rangitikei GMZ covers 1,564 km2 of farmland and forestry, as well as the rural townships of Mangaweka, Hunterville, Marton and Bulls.  To the north of Marton, groundwater use is generally limited to shallow bores that draw water from river gravels, mainly for stock water and irrigation.  To the south west, the coastal area of the zone encompasses ancient sand dune complexes which support a number of regionally significant groundwater-dependant lakes, wetlands and lagoons.

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Around 18 million years ago, the Rangitikei area was submerged beneath the sea and formed part of a large sedimentary basin where layers of marine silt, mud and clay were deposited between layers of shellbed and sand. As the sediments were uplifted, the strata were tilted and fractured by large faults and folds, trapping discrete layers of water-bearing sandstone and shell-rock between thick layers of siltstone and mudstone.  Younger sediments were laid down as shallow marine or tidal deposits, and peat and organic layers are seen throughout the sequence -the remnants of ancient wetland and lagoons.

Groundwater is abundant in the upper part of the catchment throughout the Rangitikei valley and surrounding hill country however, much of this water is moving slowly through impermeable siltstone and mudstone, known as papa, and is not accessible for use.  Groundwater in this part of the region is generally drawn from gravels that have formed along the base of the valley.  Groundwater in these gravels readily mixes with water from Rangitikei River due to the strong connection between the gravel deposits and the bed of the river.

Toward the coast, the mudstones and siltstones seen to the north are buried beneath a thick sequence of younger sediments deposited during the last few hundred thousand years.  Here, water-bearing gravels and sands are layered with impermeable silts and clays to depths of hundreds of meters below surface.  The silt and clay layers restrict the flow of groundwater within the larger leaky aquifer system.  Productive water-bearing sediments are found at various depths, near surface to more than 200 m below surface, with further potential at greater depth.

Groundwater is in high demand in the coastal area of the Rangitikei GMZ.  Changing land use during the past decade has seen much of the existing exotic forestry and remnant dune farmland converted to grazed pasture and cropping for dairy farming and intensive sheep and beef.  Low summer rainfall is common, and land owners are increasingly looking to groundwater to secure reliable water supply of water for summer irrigation. 

Agriculture now accounts for 83% of consented water use in the Rangitikei GMZ.  Public and commercial water supply accounts for 10% of the current allocation, with the remaining 10% utilised for industry and commercial operations. The total allocated annual volume of 37 million cubic meters now exceeds the water demands of the Whanganui GMZ and has the second highest consented use in the Region, following the Manawatu GMZ.

In recent years, the increasing demand for water supply for pasture irrigation has contributed to a gradual decline in seasonal groundwater levels in a number of Horizons monitoring bores. Near the coast, the Rangitikei GMZ is home to a number of wetland and coastal lake ecosystems that rely on a consistent and stable supply of groundwater to sustain them.  To ensure these lakes and wetlands and protected for future generations, Horizons works closely with local water users, iwi and the wider community to ensure water use is managed sustainably.

Water Use
Groundwater in this zone

Regional councils collect information about how much water is available and manage resource consents for those wishing to take water from groundwater supplies. Use the buttons below to view regional information on: how much water is available, where it comes from and how its used.

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Groundwater available: {{waterSource.availableToAllocate}} Irrigation
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Industrial
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Stock
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Hydroelectrical
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Town supply
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  • Groundwater in this zone
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    Groundwater in this zone

    Accurately estimating the total amount of water available in a groundwater management zone is not currently possible. Regional Councils are working with the Ministry for the Environment on the best way to calculate this figure. We will include these figures on LAWA when they become available. In the meantime, for more information about a particular groundwater management zone, contact your regional council.

    Total allocation is calculated as Daily Max Volume over 100 days for irrigation takes and Max Daily Volume over 365 days for all other uses. Estimated Annual Allocated Volume (EAAV) is calculated to determine a conservative maximum usage that may occur in a dry year and assumes that (1) for consents authorising abstraction during the irrigation season the EAAV can be calculated by assuming that, on average over a year, water is used for 100 days at 80% of the maximum consented daily abstraction rate; and (2) for consents for full year abstractions, the EAAV can be calculated by assuming that, over a year, water is used for 365 days a year at 50% of the maximum volume.

  • Water consents: How much water is consented and used?

    Groundwater available to consent

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    Consented water in this groundwater zone

    Use the tables below to look at how much water is available compared with how much is actually consented within this water management zone. Click the plus to expand subzones where available

    {{item.zoneId}}
    Comparing consents and use
    Amount available to consent In this groundwater management zone:
    {{item.data.totalAvailableAmount}} {{item.data.totalAvailableUnits}}
    available to consent
    Amount consented
    measured and non measured
    Amount used (measured)
    Amount Units Consented or used as a percentage of available
    Total available to consent {{item.data.totalAvailableAmount}} {{item.data.totalAvailableAmount}} {{item.data.totalAvailableUnits}}
    Total consented {{item.data.totalConsented.amount}} {{item.data.totalConsented.amount}} {{item.data.totalAvailableUnits}} {{item.data.totalConsented.percentText}}
    Total consented and measured {{item.data.totalMeasured.amount}} {{item.data.totalMeasured.amount}} {{item.data.totalAvailableUnits}} {{item.data.totalMeasured.percentText}}
    Total measured amount used {{item.data.totalAmountUsed.amount}} {{item.data.totalAvailableUnits}} {{item.data.totalAmountUsed.percentText}}
    Total measured volume used {{item.data.totalAnnualVolumeUsed}} {{item.data.totalAnnualVolumeUnits}}

    The table above shows the amount of water that is available for use compared to the amount that has been consented. The ‘Total Consented’ and ‘Total Consented and Measured’ fields are based on percentages of the ‘Total available to Consent’ field. If this field is not populated no data will be displayed. Some consents require actual use to be monitored and this is presented as 'Total measured volume Used' where available.

  • Water consents: How is consented water used?

    Consents by use in this groundwater zone

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    Consented water in this zone

    Overall annual volume for {{waterAvailable.year}}
    Relative breakdown
    Activity Percentage of total consented Total volume Number of consents
    {{item.displayText}} {{item.displayText}} - - No data available {{item.breakdownPercentage}}% {{item.totalVolume}} m3 {{item.numberOfConsents}}
    Total {{waterUsage.total.percentageConsented}}% {{waterUsage.total.totalVolume}} m3 {{waterUsage.total.numberOfConsents}}

    The above table shows the proportion of water consented for irrigation, industrial, stock, town supply and other. It excludes hydro electricity. In this region/management zone {{hydroUsage.totalVolume}} m3/year is consented for hydro-electricity and makes up {{hydroUsage.percentageConsented}}% of the total water volume consented for this region/management zone

    Allocation for existing hydroelectricity generation is excluded because, while it is still part of the overall allocation framework, it sits outside of the core allocation limits (i.e. the core allocation limits were set after the existing hydroelectricity take volumes).

Sites

Monitored sites in this Zone

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