The lacustrine geomorphology of Lakes Manapouri and Te Anau [article]

R. A. Pickrill, University Of Canterbury
2011
This thesis studies the lacustrine geomorphology of Lakes Manapouri and Te Anau. The shorelines of the two lakes are described and mapped. The type of shoreline produced is a product of the local geology and the effects of subaerial and lacustrine processes. Approximately three quarters of the shorelines are hard rock walls the remainder being deltaic and morainic pavements and beaches, arm head beaches and pocket sand beaches. Low lake levels have resulted in beach slumping and degradation, on
more » ... and degradation, on the pocket sand beaches where surficial sediments are thin and beach basement materials fundamentally different from the surficial deposits. The beach and nearshore relief may be likened to an ideal wave worked continental shelf in terms of both profile geometry and shore normal sediment distribution. The wind and wave climates are described and wave forecast curves prepared; the low energy and narrow range of wave forms restricts the range of morphologies produced. Both lakes have a wide natural range of lake levels ensuring that lake levels control the elevation at which an extremely limited energy resource is dissipated on the beach face. The distinctive shelf profile has been formed during low levels when wave action is highly effective in disturbing material on the outer shelf. Since the lakes have come under control the natural range of levels has been reduced and lake levels lowered, wave effectiveness on the outer shelf has been increased accordingly. The wakes produced by passing launches modify the natural wave climate particularly at beaches exposed to short fetch lengths. The magnitude, frequency and direction of wave approach are all adversely affected. The discussion of beach morphology shows the profile form of the beaches to be in equilibrium with energy and level conditions; only minor shore normal transfers of sediment are required to maintain this balance. On beaches exposed to a wide range of wave approach directions and particularly those confined by well defined barriers changes in both the profile fo [...]
doi:10.26021/9225 fatcat:zcztc4urnff4ljmptfgyqrskye