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The quantity of seasonal snow stored in the Lake Pukaki catchment, New Zealand has a significant impact on the country's economy through its influence on hydroelectricity generation, tourism, agriculture and conservation. SnowSim is a snow storage model developed for New Zealand conditions that may be used to quantify the catchment's frozen water resource and the melt water derived from that resource. Through implementation on a geographic information system, SnowSim has been applied and optimised to the Lake Pukaki catchment. The optimal parameters found were: temperature-elevation lapse rate of 0.005 ℃ m⁻¹, snow/rain temperature threshold of 2.5 ℃, and a melt to temperature relationship factor ranging from 1 to 6 mm ℃⁻¹ d⁻¹. The melt to temperature relationship factor is significantly reduced from that previously used for a New Zealand wide application of SnowSim. Use of a daily measured lapse rate was found to provide no improvement to the model, considered to be because of the spatial variability of lapse rates. Inclusion of a radiation component also provided no improvement in the model. This is contrary to the experience found in similar model applications in other regions of the world. The lower relative importance of radiation melt (with regard to total melt) in the region compared to continental l℃ations may explain this result. The use of a new precipitation distribution system did improve model results. Daily precipitation measurements were related to a new annual average precipitation surface prior to interpolating them across the region, without any elevation to precipitation relationship. Model free water results required an offset adjustment to bring them into line with measured lake inflows limiting the application of the model to estimation of seasonal variation, relative magnitudes and event frequencies of snow storage. Over four years of data a model output quality criterion of 0.61 (where a value of 1 is a perfect model) was returned. This increased to 0.76 for monthly values indicating a high quality of output at the seasonal scale. Model parameters and output quality are in line with those found using comparable models for various applications around the world. The variety of outputs available from the model provide a valuable resource for applications in the electricity, tourism, conservation and agriculture industries as well as for climate, glacier, snow and mountain research.

The quantity of seasonal snow stored in the Lake Pukaki catchment, New Zealand has a significant impact on the country's economy through its influence on hydroelectricity generation, tourism, agriculture and conservation. SnowSim is a snow storage model developed for New Zealand conditions that may be used to quantify the catchment's frozen water resource and the melt water derived from that resource. Through implementation on a geographic information system, SnowSim has been applied and optimised to the Lake Pukaki catchment. The optimal parameters found were: temperature-elevation lapse rate of 0.005 ℃ m⁻¹, snow/rain temperature threshold of 2.5 ℃, and a melt to temperature relationship factor ranging from 1 to 6 mm ℃⁻¹ d⁻¹. The melt to temperature relationship factor is significantly reduced from that previously used for a New Zealand wide application of SnowSim. Use of a daily measured lapse rate was found to provide no improvement to the model, considered to be because of the spatial variability of lapse rates. Inclusion of a radiation component also provided no improvement in the model. This is contrary to the experience found in similar model applications in other regions of the world. The lower relative importance of radiation melt (with regard to total melt) in the region compared to continental l℃ations may explain this result. The use of a new precipitation distribution system did improve model results. Daily precipitation measurements were related to a new annual average precipitation surface prior to interpolating them across the region, without any elevation to precipitation relationship. Model free water results required an offset adjustment to bring them into line with measured lake inflows limiting the application of the model to estimation of seasonal variation, relative magnitudes and event frequencies of snow storage. Over four years of data a model output quality criterion of 0.61 (where a value of 1 is a perfect model) was returned. This increased to 0.76 for monthly values indicating a high quality of output at the seasonal scale. Model parameters and output quality are in line with those found using comparable models for various applications around the world. The variety of outputs available from the model provide a valuable resource for applications in the electricity, tourism, conservation and agriculture industries as well as for climate, glacier, snow and mountain research.

Mountain precipitation, as a major component of global ecology and culture, requires diverse observation-based distribution studies to improve process characterisation and so enhance environmental management and understanding. Analysis of data from an array of precipitation gauges within the nationally important, and internationally extreme, mountainous Lake Pukaki catchment in New Zealand has been undertaken in an effort to provide such a study, while also improving local hydrological understanding. An objective observation based undercatch-corrected 1971-2000 average annual precipitation distribution has been prepared for the mountainous Lake Pukaki catchment, New Zealand. Precipitation records from 58 gauges at 51 sites, augmented with 10 new gauges, were used in preparation of the distribution. The assessed undercatch correction of 17 % across the catchment indicates that mountain hydrological investigations in New Zealand that use precipitation data and yet do not consider undercatch will be in considerable error. The average annual distribution confirms the existence of high precipitation magnitudes and horizontal gradients in the catchment in comparison with other mountain regions around the world. The high magnitude is unusual when its position in the lee of the principal orographic divide is considered indicating rare precipitation distribution processes occur in the region. Consideration of river flows, glacial change and evaporation led to a confirmation of the gauge derived average catchment precipitation. Precipitation to wind direction relationships identified the predominant westerly wind to be the primary precipitation generating direction with large magnitude events biased towards the northerly direction. All directions from the eastern side of the mountain divide had the lowest frequency and daily precipitation magnitude. Derivation of wind-classed precipitation distributions identified a distinctive south east to north west precipitation gradient for all wind directions, most severe for the north west direction and least severe for the easterly direction. Precipitation extent was greatest for the northerly direction and least for the south south westerly. The wind-classed distributions enable the estimation of daily precipitation likelihood and magnitude at any location in the catchment based on knowledge of the synoptic wind flow direction and precipitation at just one reference site. Improved river flow and lake inflow estimates resulted from the use of wind classed daily precipitation estimates validating the quality of the wind classed distributions. From 1939 to 2000 there has been no statistically significant trend in precipitation magnitudes, frequencies, or extremes in the catchment. At Aoraki/Mt Cook village, in the upper catchment, there have been significant increases in magnitude, frequency and extremes associated with the phase change of the Interdecadal Pacific Oscillation (IPO) in 1978. This change can be explained by the increase in strength of westerly winds for the different IPO phases but not by a change in frequency of different wind directions. In the lower catchment the IPO relationship is of an opposite sense to that observed in the upper catchment, indicating that the areas operate under two different climate regimes with different precipitation controls. The significant relationship to the IPO phase indicates that it is more important than climate warming in terms of future precipitation distribution in the Lake Pukaki catchment, and by extension the Southern Alps. The distributions prepared provide a valuable tool for operational and academic hydrological applications in the region. In addition, they provide a valuable characterisation of the precipitation in a Southern Hemisphere mid-latitude lee to predominant westerlies glacierized mountain catchment. From this standpoint they highlight the contrast to Northern Hemisphere mountain precipitation distributions commonly used in model validation studies, thereby providing an extension of locations with which to refine orographic precipitation process understanding.

Mountain precipitation, as a major component of global ecology and culture, requires diverse observation-based distribution studies to improve process characterisation and so enhance environmental management and understanding. Analysis of data from an array of precipitation gauges within the nationally important, and internationally extreme, mountainous Lake Pukaki catchment in New Zealand has been undertaken in an effort to provide such a study, while also improving local hydrological understanding. An objective observation based undercatch-corrected 1971-2000 average annual precipitation distribution has been prepared for the mountainous Lake Pukaki catchment, New Zealand. Precipitation records from 58 gauges at 51 sites, augmented with 10 new gauges, were used in preparation of the distribution. The assessed undercatch correction of 17 % across the catchment indicates that mountain hydrological investigations in New Zealand that use precipitation data and yet do not consider undercatch will be in considerable error. The average annual distribution confirms the existence of high precipitation magnitudes and horizontal gradients in the catchment in comparison with other mountain regions around the world. The high magnitude is unusual when its position in the lee of the principal orographic divide is considered indicating rare precipitation distribution processes occur in the region. Consideration of river flows, glacial change and evaporation led to a confirmation of the gauge derived average catchment precipitation. Precipitation to wind direction relationships identified the predominant westerly wind to be the primary precipitation generating direction with large magnitude events biased towards the northerly direction. All directions from the eastern side of the mountain divide had the lowest frequency and daily precipitation magnitude. Derivation of wind-classed precipitation distributions identified a distinctive south east to north west precipitation gradient for all wind directions, most severe for the north west direction and least severe for the easterly direction. Precipitation extent was greatest for the northerly direction and least for the south south westerly. The wind-classed distributions enable the estimation of daily precipitation likelihood and magnitude at any location in the catchment based on knowledge of the synoptic wind flow direction and precipitation at just one reference site. Improved river flow and lake inflow estimates resulted from the use of wind classed daily precipitation estimates validating the quality of the wind classed distributions. From 1939 to 2000 there has been no statistically significant trend in precipitation magnitudes, frequencies, or extremes in the catchment. At Aoraki/Mt Cook village, in the upper catchment, there have been significant increases in magnitude, frequency and extremes associated with the phase change of the Interdecadal Pacific Oscillation (IPO) in 1978. This change can be explained by the increase in strength of westerly winds for the different IPO phases but not by a change in frequency of different wind directions. In the lower catchment the IPO relationship is of an opposite sense to that observed in the upper catchment, indicating that the areas operate under two different climate regimes with different precipitation controls. The significant relationship to the IPO phase indicates that it is more important than climate warming in terms of future precipitation distribution in the Lake Pukaki catchment, and by extension the Southern Alps. The distributions prepared provide a valuable tool for operational and academic hydrological applications in the region. In addition, they provide a valuable characterisation of the precipitation in a Southern Hemisphere mid-latitude lee to predominant westerlies glacierized mountain catchment. From this standpoint they highlight the contrast to Northern Hemisphere mountain precipitation distributions commonly used in model validation studies, thereby providing an extension of locations with which to refine orographic precipitation process understanding.

This thesis investigates the shore processes of Lake Pukaki to assess the suitability and performance of existing and potential future options for management of shore hazards. Following two successive raisings of the water level in the past sixty years, Lake Pukaki’s shoreline has undergone extensive erosion. Since mid 1987 until early 1988, shoreline erosion control structures (i.e. rock revetments, gabion baskets and groynes) were constructed and maintained to protect sections of road and other assets from further encroachment of the lake shoreline. The use of the RBR XR-620 pressure sensor in this study marks the first occasion when wave statistics were measured via instrumentation at Lake Pukaki. The mean significant wave height (Hs) identified for this study was 0.53 m, while the maximum recorded wave height was 1.84 m. Similar to other alpine lakes, Lake Pukaki has characteristics of steep plunging waves. The LAKEWAVE wave hindcasting model is used to describe the wave environment about the Lake Pukaki shoreline in terms of its optimum energy potential. The maximum wave height and wave period values estimated by LAKEWAVE have been found to compare well with measured wave statistics. Under the current wave climate, experienced during this study period (July 2010 – February 2011), the majority of the assessed rock revetments seem to be performing well. The Hudson and Van der Meer formula seemed to predict respectable stability thresholds that agree with what was observed in the field. The revetment at Site 3 is the biggest concern in terms of performance based on field observations. The short-period high-magnitude storm events, eventuating from a strong north/northwest wind flow, that coincide with high lake levels tend to cause the most significant erosion along the shoreline at Lake Pukaki and have a major influence of riprap stability. Other environmental factors including the steep nearshore profile, the glacial till backshore, groundwater and precipitation were identified as controlling factors leading to the success or failure of the shore protection structures.