Geomorphological impacts of a flood event on ephemeral channels in SE Spain

A flood event occurred on 30 September 1997, in three catchments, Torrealvi lla, Salada and Nogalte, in SE Spain which were being monitored for morphol ogical change. Peak discharges were high in the Torrealvilla catchment, mod erate in the Salada and low in the Nogalte. Detailed topographic surveys we re made before and after the flood and from these DEMs of difference were c onstructed. The two sites with highest flow both underwent significant inci sion of the channel. At other sites, both scour and aggradation of the chan nel took place, with scour holes of up to 1 m depth eroded. Elsewhere, with in the channels major erosion took place downstream of tracks and structure s such as check dams that impeded sediment movement. The pattern and amount s of change show little relationship to independent factors, other than a s cale effect of peak discharge. Behaviour of channels is closely related to local sediment supply. Sediment flux calculated from changes in volumes at the site is comparable with the other figures produced for ephemeral channe ls and much higher than for perennially flowing streams. (C) 2000 Elsevier Science B.V. All rights reserved.