Flood processes and morphological changes in aggradational ephemeral rivers. Reconstruction of the October 1957 flood in the Rambla Castellarda (Spain)

Abstract

During the latter half of the twentieth century, Mediterranean ephemeral rivers underwent a profound metamorphosis. Fluvial adjustment processes narrowed the channels, simplified their planform pattern and notably reduced sediment availability. Today, this makes it extremely difficult to analyse the behaviour of this type of river in former aggradational contexts, such as those seen at the middle part of the twentieth century. For this reason, this paper addresses a reconstruction and analysis of the 1957 flood that occurred in the Rambla Castellarda, a tributary of the Turia river. The research is based, among other sources, on a series of extraordinary, high-precision aerial photographs carried out a few weeks after the flood. These images make it possible to recreate the processes observed in this ephemeral river and map the post-event river forms. Results show the behaviour of a Mediterranean aggradational ephemeral stream, very different from the current processes, and allows a comparative reflection to be made about flood processes in different sedimentary contexts. The study reveals that in-channel agricultural activity was, together with floods, the most relevant factor conditioning the river channel adjustment trajectory in that sedimentary context. Finally, the analysis of the impact of the flood in the Tura river highlights the importance of overflows – and therefore the connection between channel–floodplain – both for in-channel processes and in the lamination of floods.