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Manawatū-Whanganui region

Groundwater Zone: Horowhenua Groundwater MZ

Covering 388 square km, the Horowhenua GMZ is the smallest of Horizons' groundwater management zones. Extending from the foothills of the Tararua Range to the coast, water enters the groundwater system by direct rainfall or by seepage from streams and rivers moving through alluvial gravels, sands and silts.  A key feature of the Horowhenua GMZ is the inter-related way in which groundwater and surface water interact in streams and rivers, and in the coastal lakes

 

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Lakes Horowhenua and Papiatonga are examples of groundwater dependant ecosystems in Horizons' Region that rely on subsurface flow to sustain flow and maintain their health.  While consented groundwater use is currently well below total available annual allocation for this groundwater management zone, concerns about poor water quality in lakes, streams and rivers in the Horowhenua GMZ have lead to a revision in the amount of groundwater available in certain parts of the zone.

As with the wider Manawatu-Whanganui Basin, the groundwater environment of the Horowhenua Lakes area is considered to be a connected, multi-layerd, leaky aquifer system which becomes progressively more confined with depth.  This means that groundwater flows through and across different strata, including leakage through less permeable clay sediments.

Close to the Tararua Ranges, groundwater migrates downward from surface into deeper gravel and sand layers. Some of this water is intercepted by groundwater bores for agricultural (62%) and horticultural (29%) irrigation and water supply.  The remaining 9% of consented groundwater is used for recreational irrigation and industrial use. Non-consented shallow groundwater is also extensively utilised for private supply and stock water supply. 

The remaining portion of groundwater flows in a general coast-ward direction and discharges to the Tasman Sea. In the vicinity of Lake Horowhenua however, groundwater flow is impeded by greywacke rock which is present close to the ground surface.  Greywacke is predominant rock that forms the Tararua Ranges and it does not transport groundwater easily due to its low permeability. As groundwater moves through the more permeable gravels and sands toward the greywacke the flow is forced upwards, and into, the base of Lake Horowhenua, providing an estimated 60-66% of the total inflow to the lake.

Lake Horowhenua has received significant attention in recent years, due to on-going and persistent water quality issues.  Understanding how groundwater moves into and out of streams and lakes and what effect this has on their water quality, is crucial to informing the most effective approaches for water management and improvement of the Lake and the wider catchment. Restoration of Lake Horowhenua is a key focus for local community groups, iwi, and the wider public. A key focus of the Lake Horowhenua Accord that seeks to improve the quality and health of the Lake by addressing a number of identified issues, including improvement of groundwater quality.

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
{{waterUsage.irrigationLabel}} Industrial
{{waterUsage.industrialLabel}} Stock
{{waterUsage.stockLabel}} Hydroelectrical
{{waterUsage.hydroLabel}} Town supply
{{waterUsage.drinkingLabel}}
  • 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

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