title: Monitoring and hydrodynamic modelling of groundwater inflows into Lake Rotokakahi, New Zealand

authors: Noakes, Katie

subjects: Groundwater

abstract: Lake Rotokakahi is located 10 km south of Rotorua and is of immense cultural importance to the local iwi. The lake also has significant historical and recreational values, which prompted iwi to make the lake private in 1996. Lake Rotokakahi is one of several Rotorua/ Te Arawa lakes. Several of these lakes have become eutrophic and some have declining water quality. This study was prompted by declining water quality of Lake Rotokakahi and the need to identify potential sources of nutrients to the lake, particularly groundwater inflows.

The interaction between groundwater and surface water has a major influence on the trophic status of lakes, particularly those that are predominantly or solely groundwater fed systems. Lake Rotokakahi has one small spring-fed surface water inflow and one outflow, the Te Wairoa stream. Thus the lake is predominantly groundwater fed. The main objective of this thesis was to quantify the contribution of groundwater and surface water to Lake Rotokakahi and to examine interactions of the groundwater system with the lake, in order to provide a basis to improve lake management practices. Multiple monitoring sites were established around the perimeter of the lake to determine the spatial and temporal variation of groundwater inputs, as well as the groundwater nutrient dynamics. A three-dimensional hydrodynamic lake model was set up and simulations were used to examine how groundwater and surface water inflows were dispersed within the lake upon entry.

Monitoring of the shallow groundwater system took place from 1 January to 1 July 2016. Three separate storm events were monitored at high frequency within this monitoring period. The monitoring results showed the groundwater system varied significantly both spatially and temporally and also contributed a high proportion of the total nutrient load to the lake. Groundwater discharge and nutrient concentrations generally increased in association with or immediately following high rainfall events.
 
The three-dimensional model ELCOM was set up using hydrological data for the catchment, meteorological data from a nearby station and bathymetry of the lake. Simulations were based upon different methods of calculating groundwater inflows. Simulation 1 was based upon the common water balance equation method. Simulation 2 used constant groundwater inflow and outflow volumes as determined by a groundwater flow model, MODFLOW, which had been applied to the catchment by White et al., (2015). Simulation 3 combined MODLFOW values and measured groundwater levels to create a varying inflow volume based on water level. The three simulations accurately captured surface and bottom temperatures and had varying lake water levels. Only simulation 3 accurately captured the presence of the groundwater spring near the lake shore and was concluded the more accurate method of groundwater inflow calculation.

text: Monitoring and hydrodynamic modelling of groundwater inflows into Lake Rotokakahi, New Zealand Lake Rotokakahi is located 10 km south of Rotorua and is of immense cultural importance to the local iwi. The lake also has significant historical and recreational values, which prompted iwi to make the lake private in 1996. Lake Rotokakahi is one of several Rotorua/ Te Arawa lakes. Several of these lakes have become eutrophic and some have declining water quality. This study was prompted by declining water quality of Lake Rotokakahi and the need to identify potential sources of nutrients to the lake, particularly groundwater inflows.

The interaction between groundwater and surface water has a major influence on the trophic status of lakes, particularly those that are predominantly or solely groundwater fed systems. Lake Rotokakahi has one small spring-fed surface water inflow and one outflow, the Te Wairoa stream. Thus the lake is predominantly groundwater fed. The main objective of this thesis was to quantify the contribution of groundwater and surface water to Lake Rotokakahi and to examine interactions of the groundwater system with the lake, in order to provide a basis to improve lake management practices. Multiple monitoring sites were established around the perimeter of the lake to determine the spatial and temporal variation of groundwater inputs, as well as the groundwater nutrient dynamics. A three-dimensional hydrodynamic lake model was set up and simulations were used to examine how groundwater and surface water inflows were dispersed within the lake upon entry.

Monitoring of the shallow groundwater system took place from 1 January to 1 July 2016. Three separate storm events were monitored at high frequency within this monitoring period. The monitoring results showed the groundwater system varied significantly both spatially and temporally and also contributed a high proportion of the total nutrient load to the lake. Groundwater discharge and nutrient concentrations generally increased in association with or immediately following high rainfall events.
 
The three-dimensional model ELCOM was set up using hydrological data for the catchment, meteorological data from a nearby station and bathymetry of the lake. Simulations were based upon different methods of calculating groundwater inflows. Simulation 1 was based upon the common water balance equation method. Simulation 2 used constant groundwater inflow and outflow volumes as determined by a groundwater flow model, MODFLOW, which had been applied to the catchment by White et al., (2015). Simulation 3 combined MODLFOW values and measured groundwater levels to create a varying inflow volume based on water level. The three simulations accurately captured surface and bottom temperatures and had varying lake water levels. Only simulation 3 accurately captured the presence of the groundwater spring near the lake shore and was concluded the more accurate method of groundwater inflow calculation.

year: 2016

title: The reform of Maori land tenure and the quest for sustainability in New Zealand

authors: Jay, Grace Mairi M.

subjects: geography

abstract: Many of the countries of the Pacific region (including Australia and New Zealand) have a British colonial legacy. This history has had wide implications for the development of the region: economically, politically and socially. The cadastral (property based) systems in these countries have been influenced by British land conveyance and registration practices, and by colonial history. To date, Australia and new Zealand are still trying to resolve land tenure and information problems which are steeped in historical and ethnic dimensions. Land is the single most important factor for Maori development in New Zealand, and has great implications for the development of this country.

text: The reform of Maori land tenure and the quest for sustainability in New Zealand Many of the countries of the Pacific region (including Australia and New Zealand) have a British colonial legacy. This history has had wide implications for the development of the region: economically, politically and socially. The cadastral (property based) systems in these countries have been influenced by British land conveyance and registration practices, and by colonial history. To date, Australia and new Zealand are still trying to resolve land tenure and information problems which are steeped in historical and ethnic dimensions. Land is the single most important factor for Maori development in New Zealand, and has great implications for the development of this country.

year: 1997

title: Future research

authors: Holm, Nils G.

subjects: natural system

abstract: What field studies need to be carried out in order to test the hydrotherrnal model for the origin of life? This question was already raised in 1989 by the workshop in Prague on 'Chemical Evolution and Neo-Abiogenesis in Marine Hydrothermal Systems' (Holm, 1990). The full range and diversity of hydrothermal environments can only be revealed if more exploration work is carried out on a world-wide basis. Much progress has been made in understanding the controls on the hydrothermal fluids of individual areas, but extension to a global context remains difficult (cf. Von Datum, 1990). In Chapter 2 off-axis hydrothermal systems are discussed, pointing out that only minor surveys have been directed towards this type of hydrothermal activity, even though the amount of water which circulates through off-axis systems is estimated to exceed that of on-axis systems by a factor of between 20 and 25.

text: Future research What field studies need to be carried out in order to test the hydrotherrnal model for the origin of life? This question was already raised in 1989 by the workshop in Prague on 'Chemical Evolution and Neo-Abiogenesis in Marine Hydrothermal Systems' (Holm, 1990). The full range and diversity of hydrothermal environments can only be revealed if more exploration work is carried out on a world-wide basis. Much progress has been made in understanding the controls on the hydrothermal fluids of individual areas, but extension to a global context remains difficult (cf. Von Datum, 1990). In Chapter 2 off-axis hydrothermal systems are discussed, pointing out that only minor surveys have been directed towards this type of hydrothermal activity, even though the amount of water which circulates through off-axis systems is estimated to exceed that of on-axis systems by a factor of between 20 and 25.

year: 1992