H.L. MacMurray, T.R. Davies, and S. Ruddenklau (New Zealand)
Hydrological and Hydraulic Systems, Modelling and Simulation, Extreme Events
The Kawarau River, which drains Lake Wakatipu, is constricted by the major inflow of sediment from the Shotover River, a short distance downstream of the lake outlet. Long term records show that the water level differential across the lake outlet has reduced over the last century, which suggests that the constriction due to the Shotover River sediment is becoming more severe. Long term records also show that the annual maximum level of Lake Wakatipu is gradually rising. This is attributed to climate change, which has made the south western areas of New Zealand significantly wetter. Queenstown is a major tourist centre on the shores of Lake Wakatipu which has been flooded by high lake levels three times in recent years. Other settlements on the shores of the lake are also affected. This paper describes an investigation into management of the Shotover delta and the alluvial reach of the Kawarau River downstream of the delta, using a mobile bed physical model, and numerical hydraulic and morphological models. The models successfully reproduced the three historical flood events, and showed that in those events the system behaved in such a way as to minimise flood levels upstream of the Shotover delta.
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