We present a modelling approach for analysis of historic and future planform changes in braided rivers. We focus on two contrasting case studies: the Lower Waitaki River and the Waimakariri River. Floods in the Lower Waitaki are naturally damped by the large lakes in its headwaters, and the flow regime is further modified by the Waitaki Power Scheme. In contrast the Waimakariri is steeper and more flashy, with frequent floods. The Waitaki River is unable to clear vegetation efficiently and this, along with agricultural encroachment, has promoted a shift towards a single-thread morphology. In contrast, the more active Waimakariri River, despite having been subjected to similar vegetation, retains a largely unvegetated channel due to its ability to naturally clear vegetation. We use the model to simulate multi-decadal planform change in the two rivers, validating the model’s capability to predict the different river trajectories.
Gu (Guglielmo) Stecca and Richard Measures are scientists in NIWA’s Sediment Processes group, based in Christchurch. Gu has more than 10 years’ experience in applied mathematics, numerical modelling and river geomorphology. His key expertise is in improving, building and applying numerical models to predict the morphological evolution of river systems. Richard has 15 years’ experience in hydraulics and geomorphology related research and consulting. His current research interests are hāpua hydraulics and morphology, morphological modelling of gravel-bed rivers, surface water groundwater connections under braided rivers, flushing flow design and flood forecasting. Richard is also on the Rivers Group Committee.