Wairoa River Research Articles

A high-resolution 3D sediment-dynamics model of a morphologically complex mesotidal estuarine river system (New Zealand): insights from model calibration and validation

Land use change and the associated change in sediment runoff to the receiving environment is a topic of concern for estuarine and coastal governing agencies around the world. Fine sediments can enter the receiving environment and have a plethora of potential negative impacts (e.g., ecological, and recreational) and present no real opportunities or positive impacts. In the present study, a Delft3D numerical model is presented. The model has been calibrated considering water levels, currents, temperature, salinity, and Suspended Sediment Concentrations (SSC). Delft3D-Wave was also coupled to the hydrodynamic model to investigate the role of wave related fine sediment resuspension due to wave bed shear stresses. The extent of this model covered the Wairoa River and estuary, just south of Auckland, New Zealand. The motivation for this study was to produce a method that could link the upstream SSC contribution to the subsequent distribution in the receiving environment. From there it can readily be used as input to a regional scale model to investigate and understand the fate of sediments in the Hauraki Strait. As part of an ongoing research programme, the present study formed part of an extensive measurement campaign. Measurement instruments and results are presented alongside numerical model sensitivity analyses. The model performance is discussed, and the physical dynamics are described via extensive tables and summarising plots.

The health of cultural values and mahinga kai in the Te Wairoa-Hōpūpū-Hōnengenenge-Mātangirau, Wairoa river catchment and the impacts of sediment

ABSTRACT Te Wairoa Hōpūpū Hōnengenenge Mātangirau (Wairoa River) and its tributaries are significant to the iwi and hapū of Te Rohe o Te Wairoa in Wairoa, an area spanning northern Hawke’s Bay and southern Gisborne located on the Eastern side of Aotearoa-New Zealand’s (A-NZ) North Island. The Wairoa River is valued ecologically and for recreation and mahinga kai (food and resource gathering). The river is also affected by excess sediments. In this paper we present a cultural values framework developed in Wairoa and adapted to focus on the awa (river). Ninety two cultural value assessments were conducted with 55 people along reaches of the Wairoa river and the Waiau, its principal tributary. The data reveal considerable spatial and temporal variability in cultural health and add to knowledge of the direct and indirect impacts of sediment on cultural values. Furthermore, the data highlight the resiliency of cultural values of connectedness despite degradation to the environment, and that a range of methods can be employed to support or enhance the health of cultural values to complement water quality improvements. The use of this framework responds to the increasingly recognised need to include diverse perspectives in monitoring programmes and demonstrates that Māori-led cultural monitoring is a means to produce credible, relevant and legitimate information to support policy and planning.

Sediment dynamics of an artificially deepened mesotidal coastal lagoon: An environmental magnetic investigation of Tauranga Harbour, New Zealand

Tauranga Harbour, New Zealand's largest barrier-enclosed coastal lagoon, comprises two sub-basins with separate catchments, inlets and tidal channel systems. This study sets out to assess and investigate the sediment dispersal system of Tauranga Harbour using standard environmental magnetic and sedimentological methods. Compilations of rock magnetic and grain size data of surficial sediments collected from inflowing rivers, various estuarine environments (estuaries, tidal flats and tidal channels) and the adjacent nearshore mirror the net and differential sediment fluxes into and through the two sub-basins of this lagoon. For all studied depositional environments, the magnetogranulometric ratios SIRM/κ and ARM/κ are positively correlated with magnetic mineral content (SIRM, ARM, χ) in the sense that larger magnetic particles are associated with higher magnetic enrichment. Grain-size analyses show that magnetic enrichment during particle transport and deposition can result from grain-size as well as from grain-density fractionation. The periodically changing accumulation/erosion conditions provide for a selective retention of specific grain sizes and an enhancement of the heavier magnetic mineral particles. Magnetic crystal size and clastic grain size correlate poorly over the whole study area, but group within similar depositional environments. Coarser magnetic and clastic grain sizes and higher magnetite enrichment in the southern sub-basin can be reconciled with episodic flood runoff of the Wairoa River and a much larger, artificially deepened southern tidal inlet which likely enables higher tidal current velocities. Our approach of combining magnetic and clastic grain-size could be successfully implemented to establish a conceptual model of sediment dynamics and gravitational sorting within Tauranga Harbour.

Mercury distribution and mobility at the abandoned Puhipuhi mercury mine, Northland, New Zealand

The United Nations 2013 Minamata Convention advocates for updated environmental assessments of potential point-source sites of mercury contamination, including historic closed or abandoned mines. The Puhipuhi mercury mine (Northland), a historic and abandoned mine site, is located near one of the headwaters of the Wairoa River. In this study, total mercury levels in soils and sediments (37.8–1748 µg g−1), total and methylated mercury in waters (69.6–240 ng L−1 and 0.637–1.95 ng L−1, respectively), and elemental mercury in air (0.06–0.5 ng m−3) were measured to assess the probability and form of mercury release from the site to the surrounding natural environment. Results showed that mercury concentrations at the site are elevated compared to regional backgrounds and further work is necessary to determine how mercury may be transported from the site.

Use of one-dimensional modelling in estuary management: sediment source

This paper identifies the coastal and river borne sediment sources and serves as a background for future work that serve to investigate possible coastal prevention strategies to limit the amount of sediment influx towards the entrance of Wairoa River, thus promoting its stability. The Wairoa River, a barrier enclosed estuary situated in Hawke’s Bay, New Zealand was modelled using a one-dimensional hydrodynamic model – DYNLET. The potential rate of transport for silt, sand and gravel were investigated for both a flood flow and a median flow using the method devised by Van Rijn (J Hydraul Eng, 133(6):649–667, 2007a and J Hydraul Eng, 133(6):668–689, 2007b). The gravel found deposited at the entrance was deemed to have originated from a coastal source whereas the silt and sand were found to be a result of fluvial processes.

The hydrodynamics of the southern basin of Tauranga Harbour

The circulation of the southern basin of Tauranga Harbour was simulated using a 3-D hydrodynamic model ELCOM. A 9-day field campaign in 1999 provided data on current velocity, temperature and salinity profiles at three stations within the main basin. The tidal wave changed most in amplitude and speed in the constricted entrances to channels, for example the M2 tide attenuated by 10% over 500 m at the main entrance, and only an additional 17% over the 15 km to the top of the southern basin. The modelled temperature was sensitive to wind mixing, particularly in tidal flat regions. Residence times ranged from 3 to 8 days, with higher residence times occurring in sub-estuaries with constricted mouths. The typical annual storm events were predicted to reduce the residence times by 24%–39% depending on season. Model scenarios of storm discharge events in the Wairoa River varying from 41.69 m3/s to 175.9 m3/s show that these events can cause salinity gradients across the harbour of up to 4 PSU.

Use of one-dimensional modelling in estuary management: entrance depth –– model calibration

The Wairoa River, a barrier enclosed estuary situated in Hawke’s Bay, New Zealand was modelled using a one-dimensional hydrodynamic model. Water level data obtained during a flood and a bathymetric survey were available but the entrance cross-section had not been surveyed. This paper describes the calibration of the model to jointly optimise the selection of the Manning coefficient and the depth of the estuary entrance.

Holocene sediments and vertical tectonic downwarping near Wairoa, Northern Hawke's Bay, New Zealand

Abstract Depositional environments for Holocene terrestrial, estuarine, and marine sediments on the Wairoa River floodplain at Wairoa and coastal plain east of Wairoa, were determined from an analysis of stratigraphy, lithologies, and diatom assemblages obtained from auger holes and foundation and water-well drillholes. The sediments were deposited during the postglacial sea-level rise which started sometime prior to c. 9200 years ago and ended at c. 4000 years ago, when the shoreline was at least 2 km landward of the present position, and a ria-like morphology had developed at the innermost edge of the present-day coastal plain. The postglacial marine sediments usually occur slightly below the present sea level (down to -4 m a.m.s.l.) indicating net tectonic subsidence during the Holocene. Other evidence suggests that this tectonic subsidence may extend back into the middle Pleistocene.

230Th-238U age of Rotoehu Ash and its implications for marine terrace chronology of eastern Bay of Plenty, New Zealand

Abstract Rotoehu Ash, from the Wairoa River mouth, is dated at 71 000 ± 6000 years by the 230Th-238U radioactive disequilibrium system. The age is significantly older than the commonly quoted 14C age of 41700 ± 3500 years B.P. Marine deposits of Te Papa Terrace in the Bay of Plenty area, younger than Otamaroa Terrace of the last interglacial maximum (stage 5e), are usually conformably overlain by Rotoehu Ash. Thus, Te Papa Terrace, which emerged prior to the deposition of Rotoehu Ash, was probably formed during a global high sea-level stand at c. 85 ka. Some locations of Te Papa Terrace, however, may have been cut during an older high sea-level stand at c. 107 ka, because a peat layer occurs between marine deposits and Rotoehu Ash. Te Papa Terrace should be subdivided into two terraces which represent two successive relative high sea levels following the major high sea level of the last interglacial.

Input of river-derived sediment to the New Zealand continental shelf: II mineralogy and composition

Clay mineralogies and elemental compositions of river-borne sediments from New Zealand were examined as indicators of likely sources of the lithogenous component of sediments on the continental shelf. Relative occurrences of kaolin and smectite enabled the rivers to be fitted into three main groups. These correspond closely with geography as follows: (1) most of the rivers from North Island; (2) all the rivers from the north-east coast of South Island; (3) most of the rivers from the remainder of South Island. Elemental analyses of their sediments also led to a geographical grouping of rivers. Six main groups resulted from a Q-mode cluster analysis of elemental compositions. These were: the northernmost river (Wairoa River); the east coast of North Island; the west coast of North Island; the east coast of South Island; the south-east and west coasts of South Island; the west coast of South Island. There is substantial overlap between the groupings by clay mineralogy and by composition. The results can be interpreted mainly in terms of the geologies of source areas. Exceptions to regional trends reflect either an unusual geology in the source areas or low sediment loads, where soils contribute significantly to the sediments. The terrigenous component of offshore sediments and New Zealand riverine sediments have similar compositions, suggesting that the former are derived in a relatively unmodified form from riverine sediments.

Tereingaornis moisleyi— A new Pliocene penguin

Abstract A new genus and species of penguin, Tereingaornis moisleyi, is described from the Waipipian (mid-Pliocene) beds near Te Reinga Falls, Wairoa River, Hawke's Bay, North Island, New Zealand.

Compaction properties of bay of plenty volcanic soils, New Zealand : Parton, I M; Olsen, A J Proc 3rd Australia-New Zealand Conference on Geomechanics, Wellington, 12–16 May 1980, V1, P165–169. Publ Wellington: New Zealand Institution of Engineers, 1980

The extraordinary physical properties of soils of volcanic origin were significant in the construction of a 3.3 km earthlined headworks canal for the 20 MW Ruahihi hydro-electric power project. The scheme is the final stage of hydro-electric development on the Wairoa River for the Tauranga Joint Generation Committee. Soils at the site were found to have high natural water content, high plasticity, high sensitivity and low bulk density. These physical properties gave rise to problems during earthworks construction; namely, difficulties in excavation and compaction. These problems have since been attributed to the presence of the clay mineral allophane; similar difficulties have been reported by Northey and Schafer (1974). Perhaps the most perplexing property is that the soils undergo irreversible changes on drying. Hence compaction control values were found to lie dependent on the treatment of the soils before testing. This paper describes the engineering characteristics of the soils encountered at the site and the work carried out to establish parameters for compaction control. A range of laboratory tests were carried out to investigate the effects of pre-treatment of the soils encountered.

Mortality estimates for the rock lobster,Jasus edwardsii, near Gisborne, New Zealand

The instantaneous total (Z) and fishing (F) mortality rates were estimated for the New Zealand rock lobster, Jasus edwardsii (Hutton), along the east coast of the North Island from the Wairoa River to East Cape. Estimates of Z were made from the seasonal size‐frequency distributions (SFDs) of rock lobsters landed from five separate fishing areas for up to five fishing seasons using three different methods. Z and F were also estimated from the rate of return of tagged rock lobsters released in four of the five areas. The best estimates of Z and F for each area were considered to be estimates of F based on tag returns grouped quarterly and taken over an 8 or 9 month fishing season; estimates of Z based on these estimates of F from tag returns, with the addition of an assumed value for the annual instantaneous natural mortality rate of 0.10; and estimates of Z from the SFD analyses. These estimates were more consistent with the estimated lifespans in the fishery than were the estimates of Z derived from tag ...

Nitrate levels in subsurface waters of the Waimea Plain, Nelson

Abstract In 1969–72, nitrate determinations were made on waters from 122 wells on the Waimea Plain, Nelson, South Island, New Zealand. Four wells showed values above 30 mg NO3‐N/litre with a maximum of 50 mg/litre in one well, fifteen were in the 30–20 mg/litre range, forty‐six were between 20 mg and 10 mg/litre; fifty‐seven were below 10 mg/litre, and in only four wells was the nitrate concentration below 1.0 mg NO3‐N/litre. Where it entered the plain, the Wairoa River usually contained about 0.07 mg NO3‐N/litre, whereas the Waiiti River contained from 0.5 to 2.0 mg NO3‐N/litre. Mapping of gradients of nitrate level indicated that these might contribute to aquifer definition and to sources of replenishing waters.

Biostratigraphy and structure of Richmond Group rocks in the Wairoa River-Mount Heslington area, Nelson

Abstract A map of the Wairoa River—Mount Heslington area is presented, in which Garden Formation (new formation), Poblematica Shellbed (new fomation name), Max Sandstone (new formation), Heslington Conglomerate (new formation), Mount Wellington Sandstone, and Richmondiana Shellbed (new formation name) are shown as formations within Richmond Group, Murihiku Supergroup. The formations comprise 610 m of siltstone, sandstone, conglomerate, shellbed, and tuff exposed in sections along Wairoa River and on the slopes of Mount Heslington. The succession is repeated in the limbs of the isoclinal Heslington Syncline which appears to be non-plunging. The syncline lies north-west of Eighty-eight Fault and is itself faulted. Faunas allow recognition of Oretian, Otamitan, and Warepan stages (Upper Triassic). Stages in the evolutionary development of athyridid and spiriferinide brachiopods and the occurrence of gregarious bivalves allow refined correlation with formational units in sequences in the Southland and Kawhia synclines. Heslington Syncline appears to have an extended sequence for part of late Otamitan time. Comments on the nature and location of early fossil collections are included in an appendix.

Biostratigraphy and structure of Richmond group rocks in the Rairoa River—mount Heslington area, Nelson

Abstract A map of the Wairoa River—Mount Heslington area is presented, in which Garden Formation (new formation), Poblematica Shellbed (new fomation name), Max Sandstone (new formation), Heslington Conglomerate (new formation), Mount Wellington Sandstone, and Richmondiana Shellbed (new formation name) are shown as formations within Richmond Group, Murihiku Supergroup. The formations comprise 610 m of siltstone, sandstone, conglomerate, shellbed, and tuff exposed in sections along Wairoa River and on the slopes of Mount Heslington. The succession is repeated in the limbs of the isoclinal Heslington Syncline which appears to be non-plunging. The syncline lies north-west of Eighty-eight Fault and is itself faulted. Faunas allow recognition of Oretian, Otamitan, and Warepan stages (Upper Triassic). Stages in the evolutionary development of athyridid and spiriferinide brachiopods and the occurrence of gregarious bivalves allow refined correlation with formational units in sequences in the Southland and Kawhia ...