Braided river dynamics determined using satellite imagery — Upper Rakaia River, Canterbury, New Zealand

Abstract

The Rakaia River and its tributaries have their source high in the Southern Alps but soon flow through broad valleys and then onto the Canterbury Plains. In these wide valleys the river channel is constantly changing as more rock is weathered and eroded from the mountains to maintain the supply of gravels to the system. Beginning with a Landsat TM image from 1989 a succession of satellite images (ASTER, SPOT and Worldview 2) has been analyzed to provide quantitative data that can be interpreted in terms of river dynamics. Within the permanent, well-defined high banks, the river channel, gravels and more persistent islands have been identified for different reaches in the Upper Rakaia. Changes in the distribution of the gravels within these various reaches have been related to the geomorphologic characteristics of the associated sub-catchments.