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Marlborough region

Surface Water Zone: Opaoa River

The Opaoa River was known as the Opawa River until its name was officially changed in 2014.  The Opaoa  includes the Omaka and Taylor Rivers as major tributaries, as well as the rivers flowing through the  Benmorven, Brancott and Omaka aquifers. 

Opaoa River

The Opaoa River crosses the Wairau Plains and has been highly modified by river engineering works for flood control. It can be considered in three distinct sections:

  • The Upper Opaoa, a 13 km stretch from Renwick to Roses Overflow. Along the way it receives winter baseflow from the Omaka and Fairhall Rivers, diversions from the Wairau and Waihopai Rivers via Gibsons Creek, and some water from springs in the lower reaches. Flood flows from the Upper Opaoa are diverted away from Blenheim via Roses Overflow.
  • The Opaoa Loop, a 3km  floodgate-controlled section through east Blenheim.
  • The Lower Opaoa starts where residual flows from the Opaoa Loop join the Taylor River downstream from Riverside Park in central Blenheim. The Lower Opaoa meanders down a low gradient, tidal channel for about 15 km to join the Wairau River near the Cloudy Bay coast.

It is challenging to quantifying water flows and assess water quality trends in this changing mix of direct runoff, spring inputs and diverted water.

The contributing catchments to the Opaoa River are the dry Southern Valleys where annual rainfall can be as low as 600mm. Most of the tributaries are perennial in their upper reaches but only flow intermittently in their middle reaches before springs rejuvenate the flow in the lower reaches. The two largest contributing catchments are the Omaka and Taylor Rivers.

Omaka River

The Omaka is the largest of the dry Southern Valleys catchments to the south-west of Blenheim.  The Omaka flows generally northwards from ranges more than 1600 metres high. After leaving the confines of the hills the Omaka flows through a broad valley landscape to Renwick where it joins an old channel of the Wairau to become the Opaoa River.

The hill country catchment of the Omaka River is about 90 km2  and comprises two sub-catchments about the same size: the Omaka to the east and the Dillon to the west.  Once it leaves the hill country it flows about 20 km to Renwick.  For significant periods of the year the lower 3-5 km of the river is dry, with all water lost to natural groundwater recharge.


Water Use
Surface Water in this Zone

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


Rainfall {{waterAvailable.rainfall}} Runoff to sea {{waterAvailable.runoff}} Surface Water available: {{waterSource.availableToAllocate}} Irrigation
Town supply
  • How much surface water is there in this zone?

    Rainfall and flow in this surface water zone

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    Rainfall and runoff

    Relative breakdown Source Volume
    Rainfall total:
    {{waterAvailable.rainfall }}
    rainfall Rainfall Total {{waterAvailable.rainfall}}
    Runoff total:
    {{waterAvailable.runoff }}
    runoff Runoff to sea {{waterAvailable.runoff}}

    The table above shows the average amount of rainfall the water management zone receives each year and how much of that flows out to sea. These are approximate figures only.

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

    Surface water available to consent

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    Consented water in this surface water 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

    Comparing consents and use
    Amount available to consent In this surface water management zone:
    {{}} {{}}
    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 {{}} {{}} {{}}
    Total consented {{}} {{}} {{}} {{}}
    Total consented and measured {{}} {{}} {{}} {{}}
    Total measured amount used {{}} {{}} {{}}
    Total measured volume used {{}} {{}}

    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 in this zone are combined and displayed in the Omaka river and Taylor groundwater zones.

  • Water consents: How is consented water used?

    Consents by use in this surface water zone

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    Consented water

    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 {{}}% {{}} m3 {{}}

    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

    It excludes stock water as the taking of stock water in Marlborough is a permitted activity and a resource consent is not required or issued for this activity.

    Water use in this zone combined and displayed in the Omaka river and Taylor groundwater zones.

    The town supply activity total includes council operated schemes in both urban and rural settings as well as private communal rural schemes.


Monitored sites in this Zone

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