Lake Roxburgh is situated in the southern lakes area of the Southern Island and is used primarily for hydroelectric power generation. Roxburgh Dam was built in the 1950’s and the resulting siltation has been monitored since that time by surveying 85 cross-section profiles established at nominal 450 metre intervals along the length of the lake. The lake and gorge on the Clutha River total 31 km in length and vary in width from 50 metres to 400 metres and with a fall of some 2.5 metres during normal flows.
The river and gorge are prone to flooding during intense periods of rainfall which can cause damage to the town of Alexandra. It was proposed to flush the river and transport sediment through the gorge to the lake proper during these flooding periods by managing the lake levels. This would, over time, deepen the river, increase the hydraulic efficiency and reduce any flooding effects. The rugged nature of the canyon or gorge limits the propagation of telementry for receiving real time correction of the GPS receivers and the available satellites in view.
The full article will show how heights were obtained from GPS observation of normal-orthometric control marks to calculate a site calibration for the hydrographic project. To view the full article please see the link below.
Article: Profiling Lake Roxburgh,This article first appeared in the NZIS publication Survey Quarterly June 2013 Issue 74