Masters Thesis Abstract: Philip Mathewson
Evaluating the shoreline protection responses to widespread erosion around Lake Pukaki’s shoreline
The completion of the Pukaki High Dam in 1976 raised the surface water level of Lake Pukaki by more than 20 m, from a mean of around 493 m to a minimum of 518.2 m above mean sea level (amsl). The newly formed lake is subject to annual operational fluctuations of 14.8 m (i.e. maximum level 532 m amsl). The initial raising of the water level and fluctuation of the water surface caused widespread erosion of the surrounding shore and a net landward retreat of the shoreline. Since 1988 shoreline erosion control structures (i.e. rock revetments, gabion baskets and groynes) have been constructed and maintained in an effort to protect sections of road and other assets from further encroachment of the lake shoreline. These works have varied in the degree of success as shore protection structures, with many requiring repair, and some failing completely. Ongoing erosion in the vicinity of existing structures presents a practical problem for the managers of the lakeshore environment.
Figure 1 Rock revetment backed by a gabion wall, located on the southern shore of Lake Pukaki. State Highway 8 is to the left of the frame.
My research aims to provide an assessment of the current shoreline protection structures used to combat the ongoing erosion along the shoreline of Lake Pukaki. This will include considering the effectiveness of these protection schemes during times of variation in lake levels and storm events, and their ongoing effectiveness as the surrounding shore continues to adjust to the lake level and wave processes.
Figure 2 Weather station on the eastern shore. Mt Cook is in the background.
The wind wave regime will be examined around the lake as wind-driven wave action is the most significant natural erosive force acting on the shoreline. Two automatic weather stations will be set up on the eastern (Figure 2) and southern shores to measure wind speed, direction and duration. Wave heights and wave periods will be measured during predicted strong wind events using a RBR XR-620 pressure transducer and a WG-30 wave capacitance staff. The objective is to correlate measured wave statistics against modelled wave statistics to determine the accuracy of using wind data for wave hindcasting. Several shore profiles will be surveyed (Figure 3) around the lake to determine the slope angle of the shore. Knowledge of the shorelines geometry will be used to calculate wave run-up elevations, i.e. the maximum height waves can act on the shoreline.
Figure 3 Sokkia total station used to survey the shore profile adjacent to the eastern weather station.
For further details contact Philip on:
Email: philip.mathewson@pg.canterbury.ac.nz
Phone office: +64 3 3642987 x7910