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Ruataniwha Inlet

Ruataniwha Inlet is a moderately large-sized (~850 ha), macrotidal (3.66 m spring tidal range), shallow (mean depth ~1-2 m at high water), well-flushed (<1 day residence time). It has a single wide tidal opening (1.6 km), one large basin, and several narrow upper estuary tidal arms (largely confined within river banks), several small causeways, and extensive areas of shoreline armouring. 

The catchment (767 km2) is dominated by native forest and scrub (80%) and high producing pasture (10%), with much of the immediate estuary margin directly bordered by developed pasture /rural land, roads, causeways and seawalls. 

The estuary contains a wide variety of intertidal habitats due, in part, to the strong influence of the Aorere River which enters the estuary in the south west and where extensive cobble, gravel, sand, and biogenic (cockle, mussel, tubeworm) habitats are located in the well flushed lower reaches of the estuary.

The estuary is dominated by intertidal sand and mudflats (firm mud sands (~200 ha), firm sands (~200 ha), soft muds (~90 ha)), as well as saltmarsh (~130 ha), seagrass (~12 ha), and cobble and gravel fields (~85 ha). Historical loss of high value saltmarsh habitat is likely to have been very high. Most saltmarsh modification is likely to have occurred prior to 1950. The loss of saltmarsh habitat will primarily have been due to reclamation and drainage around margin areas.

Shoreline modification (e.g. seawalls, bunds, roads) is expected to greatly limit natural saltmarsh expansion and restrict its capacity to migrate inland in response to predicted sea level rise. Thus under predicted scenarios of increasing sea level, saltmarsh is expected to become progressively displaced in the future.

The current major estuary stressors are considered to be: disease risk for contact recreation and shellfish gathering, habitat loss, increased muddiness, and changes in biota as a result of climate change.

Broad-scale mapping using the National Estuary Monitoring protocol was conducted in 2002 and 2015 and a fine-scale survey in 2002.

Estuary summary

What makes my estuary unique?

Explore the characteristics of this estuary

Overview

Estuary characteristics

  • Total area
    ~850 hectares
  • Tide
    3.66 m spring tidal range
  • Flushing time
    <1 day

What's happening upstream?

See results from monitored river quality sites influencing this estuary

River quality

What's happening upstream?

The physical characteristics and health of estuaries are influenced by the rivers and streams flowing into them. For instance, when it rains the mud and contaminants generated on land can be washed into rivers and eventually flow into the estuary. The health of our rivers and streams can therefore be very important for Estuary Health, and understanding the upstream pressures can help with interpreting estuary monitoring data. Monitoring is undertaken for a range of river health indicators (e.g., water quality and ecology) in many catchments across the region. Where there are monitored river catchments that influence this estuary, these are shown below. You can click through to view monitoring results from these River Quality sites to see current state and how health has changed over time.

What surrounds my estuary?

See land cover information from monitored catchments that surround this estuary

Land cover

What surrounds my estuary?

The physical characteristics and health of estuaries are influenced by local geography and the way we use our land. This is because estuaries are the receiving environments for many of our land use activities. Land cover information can be used as an indicator of land use, therefore knowing the surrounding land cover can help us understand which pressures might be affecting Estuary Health. For example, the sandflats of estuaries surrounded by rural areas will typically contain contaminants related to rural activities (e.g., cadmium from crop fertilisers and copper from fungicides), whereas those surrounded by urban areas are more likely to contain contaminants associated with cities (e.g., zinc and lead from roads and building materials). Where there is land cover information available for nearby catchments, these are listed below. These figures show the types of vegetation and built or natural features that surround the estuary margins and the rivers that flow into this estuary. You can click through to the Land Cover topic to see these land cover classes broken down into further detail, and view changes over time.

Aorere

What do the Broad Land Cover Classes mean?

Land cover information on LAWA is grouped into land cover classes at two levels of detail – broad and medium. For this overview we are showing the six broad-level classes for the catchment.

  • Forest

    Inclusive of; indigenous and exotic forest.

  • Scrub / shrubland

    Inclusive of; indigenous and exotic scrub / shrubland.

  • Grassland / other herbaceous vegetation

    Inclusive of; tussock and exotic grassland and other herbaceous vegetation.

  • Cropland

    Inclusive of; cropping / horticulture.

  • Urban / bare / lightly-vegetated surfaces

    Inclusive of; natural bare/lightly-vegetated and artificial bare surfaces, and urban area

  • Water bodies
Monitored sites 4

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