The project aims to resolve flooding issues currently affecting the lower reaches of the Tangaroa catchment, as well as improve water quality, restore native fish habitat and biodiversity, and return mauri to an awa (river) of cultural significance. The work takes a holistic approach to stormwater management, with restoration across a range of land ownership within the awa corridor. The land within the catchment is either Māori land, or owned by Ministry of Education or NPDC.
Within the Tangaroa catchment there are buildings at risk of flooding during significant flood events. This flood risk is the result of overflows from the Tangaroa Stream flowing through private property, as well as several dwellings located in low-lying land relative to the Waitara River that cannot drain when the river is in flood.
There is risk of damage to private property and Council infrastructure during floods. High-velocity overflows from the Tangaroa Stream onto North Street can affect the stability of foundations and poles through scouring, are a danger to personal safety, can cause structural damage to buildings and roads, and affect flood evacuation and emergency routes.
During small to medium-sized rainfall, there is extensive surface ponding on Princess Street and surrounding roads, resulting in health and safety concerns for residents. Some of these roads do not have kerb and channel or modern drainage. These cannot be installed because currently there is not a proper outfall for the flows into the Waitara River, and the additional runoff would exacerbate the flood risk downstream.
Unfortunately, water quality, mauri and stream health have degraded over time. As a result, the connection of the local community with the stream, as well as an understanding of the Tangaroa’s significance, have deteriorated.
Intensification of urban land use has led to piping significant portions of the waterway. Of note, more than 100m is piped through Owae Marae adjacent to the historic Manukorihi pā. The waterway is also redirected to a 150m piped section below North Street, cutting off the original outlet to the river.
Several sections of the waterway are overwhelmed by invasive vegetation which results in stagnant and decreased water flows and loss of biodiversity. Invasive species prevent the natural regeneration of the native riparian and wetland ecosystems.
Water quality is poor in terms of E-coli and nitrogen when compared to freshwater bathing standards.
There are several barriers to fish passage including the piped section on North Street. Upstream of the pipe, only longfin eels and triplefins were observed in 2020 NIWA survey. Downstream of the pipe and on comparable streams, banded kōkopu, bully, inanga, short fin eel and other species are present, suggesting that the barriers significantly affect fish biodiversity and density upstream.
Clean, clear and flowing/running
Tangaroa used to be a healthy open stream and the reinstatement of that continuous and clean flow is important for the reconnection of the community to the stream.
These upgrades will be the backbone of the stormwater network that the catchment currently lacks, to deal with existing flooding issues.
The pipe along North Street that conveys the water to the Waitara River is undersized, and will be upgraded to convey the flows from a one in 100 year rainfall event (1% AEP with climate change allowance). The inlet and outlet of that pipe will also be upgraded.
A flood diversion structure will be created at the top of North Street to ensure that only high flows during significant rainfall get into the pipeline, while the normal flow will be maintained within the stream. This will reinstate the Tangaroa’s original connection with the Waitara River.
An additional section of pipe will connect the North Street diversion structure with Princess Street, along Richmond Street. This will allow an outlet for future improvements in the Princess Street stormwater network, although these are not part of the Tangaroa project.
This part of the works will recognise and provide for sites of cultural significance, improve water quality and habitat biodiversity, and enhance the mauri (life force/essence) to an awa of cultural significance. Restoration works will include:
The delivery timeframe of Tangaroa Restoration is five years, from 2021 to 2026. The first year (2021/22) has been focused on design and consultation. The project has been co-designed in partnership through the Waitara Stormwater Working Party, formed by NPDC staff and representatives of hapū and iwi.
Physical works start in 2022/23, beginning with the construction of the first section of pipeline at Richmond Street, between the marae entrance and Princess Street.
The project budget is $5.8m, with NPDC contributing $4m from the Waitara Stormwater Programme and the the Ministry for the Environment contributing $1.8m through the Freshwater Improvement Funds programme. The majority of the NPDC contribution is going towards the stormwater infrastructure upgrades.
The MfE contribution to the project is to fund the restoration work, and it is linked to the achievement of specific objectives, related to the empowerment of the local community to exercise kaitiakitanga of the stream, creation of employment and education opportunities, and restoration of the cultural and ecological values of the awa.
Tangaroa was the name given to a channel near the Waitara River mouth and served as a tauranga waka (mooring site) for waka arriving at Manukorihi Pā, a 12-acre fortified complex located on a headland bounded by the Waitara River and overlooking the river mouth.
Tangaroa is a name also given to a freshwater stream that emerged from a puna (spring) at the south-eastern point of Manukorihi Pā and flowed in a north-westerly arc down the western headlands to Tangaroa harbour.
The Tangaroa Stream formed a natural boundary for Manukorihi Pā and was crucial to the safe and favourable living conditions of many generations. The puna and upper course was a site for ritual activity.
Tangaroa supported an ecosystem of indigenous flora and fauna. It also sustained the abundant wetlands at Manukorihi Pā where harakeke and raupo were grown and harvested for a wide variety of uses, and was home to numerous fish and insect species and a feeding ground for birds – the name ‘Manukorihi’ referring to their morning chorus, ‘a place where birds sing’.
Tangaroa Stream irrigated the extensive cultivations on the sheltered alluvial terrace below Owae Marae, which stretched down to the canoe harbour and were capable of supporting large gatherings in times of peace and war. In times of war, Tangaroa contributed to the impregnable defence system of Manukorihi Pā. The stream and wetlands provided a natural obstacle in front of the palisade line connected by a chain of east-facing defence forts. Tangaroa was also the primary source of freshwater, used to raise fish stocks and process various foods.
In the 1820s, during the sustained war with Waikato Māori, Manukorihi Pā was depopulated with the Tangaroa wetlands serving as a repository for the famed whakairo produced at Wharekura Marae within the Manukorihi Pā complex.
Manukorihi rose again in the late 1840s as a centre of resistance against land sales to the British Crown. Our opposition led to the outbreak of war with the Crown between 1860/61, which resulted in wholesale land confiscation under the 1863 New Zealand Settlements Act.
In 1883, The West Coast Reserves Settlement Commission allocated the 25-acre Manukorihi Block, which enabled Manukorihi Hapu to resettle in Waitara. Designated as a ‘native reserve’ vested with the Public Trustee, the Manukorihi Block included the central section of the Tangaroa watercourse. The puna, upper section and lower section of the waterway lay outside the Crown Grant area and were converted to individual land titles for residential and rural purposes.
From 1883, the Tangaroa water system ceased to be regarded as a whole entity and was subjected to despoliation by adjoining landowners.
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Page last updated: 09:51AM Thu 26 January 2023