title: The Sediment Dynamics of Ahuriri Estuary, Napier, New Zealand

authors: Eyre, Tracey Michelle

subjects: Ahuriri

abstract: Ahuriri Estuary is a shallow, microtidal estuary located in Hawke's Bay, New Zealand. Sediment transport pathways and areas of potential erosion and accretion of Ahuriri Estuary are identified to enhance the understanding of the fate of contaminants entering the estuary and to provide a basis for future large-scale modelling applications. Fine sediments have a high adsorption capacity for heavy metals and nutrients, which may result in the accumulation of contaminants in estuarine environments. Extensive land claim of previously inundated areas uplifted by the 1931 Napier earthquake for industrial, urban and agricultural expansion has led to an increase in heavy metal and nutrient runoff into the estuary. Characterising the hydrodynamics and sediment transport of the estuary is imperative for the prediction and mitigation of sedimentation and contaminant accumulation.
A combination of hydrodynamic and sediment transport modelling using the DHI MIKE 21 suite was used to run a series of scenarios of sediment release into the estuary and subsequent dispersal. The MIKE 21 Flow model was calibrated and validated using field data from two field deployments conducted during a spring and neap tide. The hydrodynamic model predicted current direction and velocity patterns in concurrence with measured data. Residual circulation patterns in Ahuriri Estuary were ebb-dominated, indicating a likely net downstream movement in sediment. Flow was highly channelised within the middle - lower estuary, with a low energy regime in the upper estuary. This suggested that sediment introduced into the estuary from the Taipo Stream is likely to be flushed from the estuary if it reached the middle estuary. However, flow velocities and lack of residual currents in the upper estuary resulted in a large proportion of sediment introduced during storm runoff settling out of suspension, resulting in net deposition in close proximity to the source. 
Sediment grain-size and consequently the settling velocity were found to be the main contributing factor to sediment dispersal. Fine silts were found to be transported the furthest downstream with a large proportion being transported from the estuary mouth and the model domain, respectively. A large proportion of coarser silts and fine sands were found to settle out of suspension in close proximity to the sediment source. An increased settling velocity resulted in an increased influence of the simulation conditions at the time of sediment release, as it was the initial transport of coarser grain-sizes which determined their ultimate depositional location. Sediment deposition was greatest in close proximity to the source and in upper intertidal regions, which are a major sink for suspended sediments due to their sheltered nature. This was correlated with greater organic carbon content and finer grain-sizes in these areas, suggesting a depositional environment. A general trend of fining of grain-size from high energy to low energy environments was identified. In these areas, sediment reworking due to tidal action and wave-related processes was limited.

text: The Sediment Dynamics of Ahuriri Estuary, Napier, New Zealand Ahuriri Estuary is a shallow, microtidal estuary located in Hawke's Bay, New Zealand. Sediment transport pathways and areas of potential erosion and accretion of Ahuriri Estuary are identified to enhance the understanding of the fate of contaminants entering the estuary and to provide a basis for future large-scale modelling applications. Fine sediments have a high adsorption capacity for heavy metals and nutrients, which may result in the accumulation of contaminants in estuarine environments. Extensive land claim of previously inundated areas uplifted by the 1931 Napier earthquake for industrial, urban and agricultural expansion has led to an increase in heavy metal and nutrient runoff into the estuary. Characterising the hydrodynamics and sediment transport of the estuary is imperative for the prediction and mitigation of sedimentation and contaminant accumulation.
A combination of hydrodynamic and sediment transport modelling using the DHI MIKE 21 suite was used to run a series of scenarios of sediment release into the estuary and subsequent dispersal. The MIKE 21 Flow model was calibrated and validated using field data from two field deployments conducted during a spring and neap tide. The hydrodynamic model predicted current direction and velocity patterns in concurrence with measured data. Residual circulation patterns in Ahuriri Estuary were ebb-dominated, indicating a likely net downstream movement in sediment. Flow was highly channelised within the middle - lower estuary, with a low energy regime in the upper estuary. This suggested that sediment introduced into the estuary from the Taipo Stream is likely to be flushed from the estuary if it reached the middle estuary. However, flow velocities and lack of residual currents in the upper estuary resulted in a large proportion of sediment introduced during storm runoff settling out of suspension, resulting in net deposition in close proximity to the source. 
Sediment grain-size and consequently the settling velocity were found to be the main contributing factor to sediment dispersal. Fine silts were found to be transported the furthest downstream with a large proportion being transported from the estuary mouth and the model domain, respectively. A large proportion of coarser silts and fine sands were found to settle out of suspension in close proximity to the sediment source. An increased settling velocity resulted in an increased influence of the simulation conditions at the time of sediment release, as it was the initial transport of coarser grain-sizes which determined their ultimate depositional location. Sediment deposition was greatest in close proximity to the source and in upper intertidal regions, which are a major sink for suspended sediments due to their sheltered nature. This was correlated with greater organic carbon content and finer grain-sizes in these areas, suggesting a depositional environment. A general trend of fining of grain-size from high energy to low energy environments was identified. In these areas, sediment reworking due to tidal action and wave-related processes was limited.

year: 2009

title: Lake Tutira: historic water quality, monitoring recommendations and management options

authors: Abell, Jonathan Michael

abstract: Lake Tutira is located 30 km north of Napier and is an important recreational resource for the Hawke's Bay region. The lake has an area of 1.74 km², mean depth of 21 m and maximum depth of 42 m. It has a recent history of poor water quality, and over 2011 and 2012 there were severe blooms of blue-green algae (cyanobacteria), which detracted from the ecological and aesthetic value of the lake, and impacted on its suitability for recreational use.
We analysed the recently-available (2009-2012) monitoring data for Lake Tutira, which included periods of regular (c. monthly) water quality monitoring measurements, as well as data from an automated high-frequency monitoring buoy. Poor water quality in Lake Tutira is not a recent problem and TLI values in the 1960s and 1970s were higher than those for the analysis period. High-frequency buoy data demonstrated that high-intensity rainfall events produced rapid increases in water level and increased turbidity. Increases in chlorophyll fluorescence a few days after major rainfall events indicate that rainfall events may also stimulate increases in phytoplankton biomass in the lake via increased nutrient inputs associated with stormflows.
Grass carp were introduced into Lake Tutira in 2008 to control the invasive weed Hydrilla which had been present in the lake for some decades. There has been a rapid reduction in Hydrilla beds in the lake following the grass carp introduction. We recommend that the impact of grass carp on Lake Tutira be evaluated from an ecosystem perspective, given some marked changes in other components of the lake ecosystem since the introduction.
We evaluated the suitability of Lake Tutira for application of an ecological model to assist with consideration of management options to improve lake water quality. Lake Tutira is a suitable candidate lake for both one-dimensional (1-D; vertically resolved) and three-dimensional (3-D) ecological model applications to represent the vertical variations and whole-lake water column variations, respectively. A comprehensive ecological model of Lake Tutira could be used to simulate the outcomes of various lake restoration strategies, thus acting as a decision support tool for proposed lake management actions. The likely performance of a model application and hence its value for informing management decisions could be improved considerably with substantial additional data collection (e.g. inflow water quality), as well as continuation of the current lake monitoring. A number of potential management options were considered for Lake Tutira and we recommend that these options be considered further with the 1-D and/or 3-D models in order to fully assess their feasibility, effectiveness and value for money.

text: Lake Tutira: historic water quality, monitoring recommendations and management options Lake Tutira is located 30 km north of Napier and is an important recreational resource for the Hawke's Bay region. The lake has an area of 1.74 km², mean depth of 21 m and maximum depth of 42 m. It has a recent history of poor water quality, and over 2011 and 2012 there were severe blooms of blue-green algae (cyanobacteria), which detracted from the ecological and aesthetic value of the lake, and impacted on its suitability for recreational use.
We analysed the recently-available (2009-2012) monitoring data for Lake Tutira, which included periods of regular (c. monthly) water quality monitoring measurements, as well as data from an automated high-frequency monitoring buoy. Poor water quality in Lake Tutira is not a recent problem and TLI values in the 1960s and 1970s were higher than those for the analysis period. High-frequency buoy data demonstrated that high-intensity rainfall events produced rapid increases in water level and increased turbidity. Increases in chlorophyll fluorescence a few days after major rainfall events indicate that rainfall events may also stimulate increases in phytoplankton biomass in the lake via increased nutrient inputs associated with stormflows.
Grass carp were introduced into Lake Tutira in 2008 to control the invasive weed Hydrilla which had been present in the lake for some decades. There has been a rapid reduction in Hydrilla beds in the lake following the grass carp introduction. We recommend that the impact of grass carp on Lake Tutira be evaluated from an ecosystem perspective, given some marked changes in other components of the lake ecosystem since the introduction.
We evaluated the suitability of Lake Tutira for application of an ecological model to assist with consideration of management options to improve lake water quality. Lake Tutira is a suitable candidate lake for both one-dimensional (1-D; vertically resolved) and three-dimensional (3-D) ecological model applications to represent the vertical variations and whole-lake water column variations, respectively. A comprehensive ecological model of Lake Tutira could be used to simulate the outcomes of various lake restoration strategies, thus acting as a decision support tool for proposed lake management actions. The likely performance of a model application and hence its value for informing management decisions could be improved considerably with substantial additional data collection (e.g. inflow water quality), as well as continuation of the current lake monitoring. A number of potential management options were considered for Lake Tutira and we recommend that these options be considered further with the 1-D and/or 3-D models in order to fully assess their feasibility, effectiveness and value for money.

year: 2013

title: Matariki, commodity culture, and multiple identities

authors: Hardy, Ann

subjects: Matariki

abstract: The event known as Matariki, the rising of the Pleiades in winter, which Māori take as the mark of the beginning of a new year, was not a strong feature of the wider public sphere for most of the 20th century. Since 2001, however, when Te Taura Whiri, the Māori Language Commission, published an explanatory booklet with the aim of reviving interest in Matariki as an aide to the maintenance of te reo, it has been promoted by several quasi-governmental institutions, especially the national museum, Te Papa, as a winter festival for all New Zealanders. Its main public presence to date has been through media products: posters, banners, websites, television programmes, newspaper features, calendars, some theatrical performances and physical commemoration ceremonies.

The larger project, of which this paper represents an initial descriptive and positioning phase, is a continuation of the researcher's long-standing interest in the intersections of religiosity, culture, and media as they are active in the environment of Aotearoa New Zealand. It assumes, building on theorists such as Bellah and Lundby that the creation of such festivals is an act of 'civil religiosity' that attempts to create and strengthen national community around a set of numinous symbols.
However, the development of an enterprise such as Matariki is pursued in a complex political field, where broad agreement across various factions is needed before the festival can take on an enduring material and symbolic existence. In investigating the factors that will determine the future of Matariki it is relevant to consider the interaction of three factors in particular: the ethno-political history of New Zealand; the characteristics of contemporary reflexive spirituality, which are intertwined with commodificatory tendencies and thirdly, the impacts of increasing globalisation on the parameters of identity-formation for citizens in late-modern societies.

text: Matariki, commodity culture, and multiple identities The event known as Matariki, the rising of the Pleiades in winter, which Māori take as the mark of the beginning of a new year, was not a strong feature of the wider public sphere for most of the 20th century. Since 2001, however, when Te Taura Whiri, the Māori Language Commission, published an explanatory booklet with the aim of reviving interest in Matariki as an aide to the maintenance of te reo, it has been promoted by several quasi-governmental institutions, especially the national museum, Te Papa, as a winter festival for all New Zealanders. Its main public presence to date has been through media products: posters, banners, websites, television programmes, newspaper features, calendars, some theatrical performances and physical commemoration ceremonies.

The larger project, of which this paper represents an initial descriptive and positioning phase, is a continuation of the researcher's long-standing interest in the intersections of religiosity, culture, and media as they are active in the environment of Aotearoa New Zealand. It assumes, building on theorists such as Bellah and Lundby that the creation of such festivals is an act of 'civil religiosity' that attempts to create and strengthen national community around a set of numinous symbols.
However, the development of an enterprise such as Matariki is pursued in a complex political field, where broad agreement across various factions is needed before the festival can take on an enduring material and symbolic existence. In investigating the factors that will determine the future of Matariki it is relevant to consider the interaction of three factors in particular: the ethno-political history of New Zealand; the characteristics of contemporary reflexive spirituality, which are intertwined with commodificatory tendencies and thirdly, the impacts of increasing globalisation on the parameters of identity-formation for citizens in late-modern societies.

year: 2011