title: Reduction of water and bed levels in the lower Waikato River

authors: Wo, You Gu

subjects: Waikato River

abstract: The major aims of this thesis are to determine the historical qualitative and quantitative reduction in water and bed levels of the lower Waikato River, to identify probable factors influencing the reduction, and to predict the future water and bed levels at Huntly in relation to the Huntly Power Station management
Sediments in the Waikato River are composed of gravelly pumiceous sands. In terms of the mean and median grain sizes, generally sands dominate the lower river b~ from the river mouth to the cross section at about 100 km upstream of the mouth, while gravels dominate the bed upstream onward. A hiatus in the longitudinal mean and median grain size distributions from sand to gravel is apparent around Horotiu. In the Waipa River, the texture of bed materials was found to be similar but probably finer to those in the lower parts of the Waikato River.
On the basis that ∂n / ∂Q= ∂W/ ∂Q =∂S / ∂Q=0, where n, W, S and Q are, respectively, Manning's coefficient, width, energy slope and discharge, water level of each gauging can be adjusted to one for an index flow of 350 m³/s ( WLQ₌₃₅₀ ). Further assuming that ∂n / ∂T = ∂W / ∂T = ∂S / ∂T=0 where T is time, variations in the time series of WLQ₌₃₅₀ represent the mean bed level changes over time. These assumptions seem to be acceptable for those gauging data within a certain range of discharges in the lower Waikato River.
A quantitative analysis of the available river survey data, water level profile measurements, and gauging records has indicated that, in general, there was a continuous trend of reduction in water and bed levels on the lower Waikato River since the 1960s. The reasons for these reductions likely include sand mining operation along the river, consequent disturbance of the river bed surface, long term sand extraction around Mercer and further downstream, upstream effects of the significant bed level lowering at Mercer, and downstream effects of the 1947 Karapiro Dam closure.
Analysis of river bulk volume changes suggested that the amount of bedload transported into the river downstream of Ngaruawahia was about 160 000±24 000 m3/yr between 1964-1989. Nearly two-thirds of this was contributed by the bed materials stored in the upstream Waikato River course by an analysis of data from 1974-1989, and the remainder by the Waipa River and the catchment yield from the Hamilton basin.
Two disparate time scales for water and bedload movements in practice result in singularperturbation characteristics of the system. With a quasi-steady flow approach, linearization of the water and bedload movement system produces a hyperbolic equation or even a parabolic equation (uniform flow). The parabolic equation is a good approximation of the hyperbolic equation under the condition of large values of time or a large distance from the original disturbance. Variations along the Waikato River of an average mean bed level within a certain length of channel are expected to be small. Therefore the linear models can be applied. In the domain between 48.25-94.45 km upstream of the Waikato River mouth, the parabolic model has been used numerically to predict the future bed levels at Huntly in December 2040 for different scenarios. Potential effects on operation of the present cooling water system have been assessed for given discharges at that time.
The ratio of river width to water depth for the formation of alternate bars at the Huntly Railway Bridge has been found to be exceeding 100 by an analysis of the gauging data at this site and at the Ngaruawahia Cableway. This critical width-depth ratio, 100, is much bigger than those suggested in the literature. The corresponding conditions of discharge and mean water depth are, respectively, less than about 350 m³/s and 2.30 m. However further research is required to confirm these conclusions.

text: Reduction of water and bed levels in the lower Waikato River The major aims of this thesis are to determine the historical qualitative and quantitative reduction in water and bed levels of the lower Waikato River, to identify probable factors influencing the reduction, and to predict the future water and bed levels at Huntly in relation to the Huntly Power Station management
Sediments in the Waikato River are composed of gravelly pumiceous sands. In terms of the mean and median grain sizes, generally sands dominate the lower river b~ from the river mouth to the cross section at about 100 km upstream of the mouth, while gravels dominate the bed upstream onward. A hiatus in the longitudinal mean and median grain size distributions from sand to gravel is apparent around Horotiu. In the Waipa River, the texture of bed materials was found to be similar but probably finer to those in the lower parts of the Waikato River.
On the basis that ∂n / ∂Q= ∂W/ ∂Q =∂S / ∂Q=0, where n, W, S and Q are, respectively, Manning's coefficient, width, energy slope and discharge, water level of each gauging can be adjusted to one for an index flow of 350 m³/s ( WLQ₌₃₅₀ ). Further assuming that ∂n / ∂T = ∂W / ∂T = ∂S / ∂T=0 where T is time, variations in the time series of WLQ₌₃₅₀ represent the mean bed level changes over time. These assumptions seem to be acceptable for those gauging data within a certain range of discharges in the lower Waikato River.
A quantitative analysis of the available river survey data, water level profile measurements, and gauging records has indicated that, in general, there was a continuous trend of reduction in water and bed levels on the lower Waikato River since the 1960s. The reasons for these reductions likely include sand mining operation along the river, consequent disturbance of the river bed surface, long term sand extraction around Mercer and further downstream, upstream effects of the significant bed level lowering at Mercer, and downstream effects of the 1947 Karapiro Dam closure.
Analysis of river bulk volume changes suggested that the amount of bedload transported into the river downstream of Ngaruawahia was about 160 000±24 000 m3/yr between 1964-1989. Nearly two-thirds of this was contributed by the bed materials stored in the upstream Waikato River course by an analysis of data from 1974-1989, and the remainder by the Waipa River and the catchment yield from the Hamilton basin.
Two disparate time scales for water and bedload movements in practice result in singularperturbation characteristics of the system. With a quasi-steady flow approach, linearization of the water and bedload movement system produces a hyperbolic equation or even a parabolic equation (uniform flow). The parabolic equation is a good approximation of the hyperbolic equation under the condition of large values of time or a large distance from the original disturbance. Variations along the Waikato River of an average mean bed level within a certain length of channel are expected to be small. Therefore the linear models can be applied. In the domain between 48.25-94.45 km upstream of the Waikato River mouth, the parabolic model has been used numerically to predict the future bed levels at Huntly in December 2040 for different scenarios. Potential effects on operation of the present cooling water system have been assessed for given discharges at that time.
The ratio of river width to water depth for the formation of alternate bars at the Huntly Railway Bridge has been found to be exceeding 100 by an analysis of the gauging data at this site and at the Ngaruawahia Cableway. This critical width-depth ratio, 100, is much bigger than those suggested in the literature. The corresponding conditions of discharge and mean water depth are, respectively, less than about 350 m³/s and 2.30 m. However further research is required to confirm these conclusions.

year: 1994

title: New Zealand

authors: Moffat, Kirstine

subjects: New Zealand

abstract: 2009 was a particularly rich and diverse year for New Zealand literature, with the publication of significant works by many established authors and the emergence of several new and promising voices. Experimentation with form and a joyful celebration of the act of creation are a hallmark of much of this year’s bibliography. The first decade of the twenty-first century continues to be distinguished by a range of genres and forms – realist, mythic, fantastical and historical modes remain particularly popular – and, in some authors’ work, by a movement away from New Zealand settings to other, actual or imagined, locations.

text: New Zealand 2009 was a particularly rich and diverse year for New Zealand literature, with the publication of significant works by many established authors and the emergence of several new and promising voices. Experimentation with form and a joyful celebration of the act of creation are a hallmark of much of this year’s bibliography. The first decade of the twenty-first century continues to be distinguished by a range of genres and forms – realist, mythic, fantastical and historical modes remain particularly popular – and, in some authors’ work, by a movement away from New Zealand settings to other, actual or imagined, locations.

year: 2010

title: The biology and general ecology of the Koaro (Galaxias brevipinnis) in some tributary streams of Lake Taupo

authors: Kusabs, Ian Andrew

abstract: The ecology and general biology of Galaxias brevipinnis were studied in three tributary streams of Lake Taupo between May 1988 and April 1989. Adult koaro were found in relatively high densities in the Waipehi and Omori streams but in low densities in the larger Waiotaka stream. The results of population estimation studies suggest that the distribution and abundance of koaro is negatively correlated with that of trout. There was a general decline in the population density of stream-resident koaro in the winter months. Juvenile koaro were found to migrate into the tributaries from August to December, with migrations being at a peak in October and November.

Population length-frequency distributions and otoliths used to age koaro indicated that there were up to 5 age classes. Growth was allometric and was adequately described by the von Bertalanffy equation after the first year of life. Koaro were found to be in best condition in the Spring and lowest in Winter.

Spawning appeared to occur from December through to April peaking in late Summer to early in the Waipehi Stream was Autumn. The mean fecundity of koaro approximately 5500. A sex-ratio of approximately 1:1 (males: females) were found in the koaro populations in the Omori and Waipehi streams, but during spawning there were always more ripe males than gravid females.

There was considerable overlap in the diets of both koaro and juvenile rainbow trout in the Waipehi and Omori streams, with invertebrates being consumed according to their relative abundance in the benthos. Ephemeroptera larvae were numerically the most important food item in the diet of both species. However, by weight, fish (juvenile koaro) were the most important food · item in the diet of koaro and rainbow trout in the Waipehi stream. In the Omori stream in Winter, trout eggs were the most important food item in terms of weight. Terrestrial prey was found to be of relatively minor importance in the diets of koaro and rainbow trout in the Waipehi and Omori streams.

text: The biology and general ecology of the Koaro (Galaxias brevipinnis) in some tributary streams of Lake Taupo The ecology and general biology of Galaxias brevipinnis were studied in three tributary streams of Lake Taupo between May 1988 and April 1989. Adult koaro were found in relatively high densities in the Waipehi and Omori streams but in low densities in the larger Waiotaka stream. The results of population estimation studies suggest that the distribution and abundance of koaro is negatively correlated with that of trout. There was a general decline in the population density of stream-resident koaro in the winter months. Juvenile koaro were found to migrate into the tributaries from August to December, with migrations being at a peak in October and November.

Population length-frequency distributions and otoliths used to age koaro indicated that there were up to 5 age classes. Growth was allometric and was adequately described by the von Bertalanffy equation after the first year of life. Koaro were found to be in best condition in the Spring and lowest in Winter.

Spawning appeared to occur from December through to April peaking in late Summer to early in the Waipehi Stream was Autumn. The mean fecundity of koaro approximately 5500. A sex-ratio of approximately 1:1 (males: females) were found in the koaro populations in the Omori and Waipehi streams, but during spawning there were always more ripe males than gravid females.

There was considerable overlap in the diets of both koaro and juvenile rainbow trout in the Waipehi and Omori streams, with invertebrates being consumed according to their relative abundance in the benthos. Ephemeroptera larvae were numerically the most important food item in the diet of both species. However, by weight, fish (juvenile koaro) were the most important food · item in the diet of koaro and rainbow trout in the Waipehi stream. In the Omori stream in Winter, trout eggs were the most important food item in terms of weight. Terrestrial prey was found to be of relatively minor importance in the diets of koaro and rainbow trout in the Waipehi and Omori streams.

year: 1989