Assessment of channel changes in a Mediterranean ephemeral stream since the early twentieth century. The Rambla de Cervera, eastern Spain

- Aerial photographs and GIS were used to quantify changes in stream corridor.
- The Rambla de Cervera channel losts width (68.5%) and surface area (45.7%).
- The incision processes occurred along the study reach at an average depth of 3.5 m.
- Land use changes and gravel mining are the causal factors of the corridor changes.
- Changes are forced by randomness in flood frequency.

An analysis of morphological changes during the last six decades is presented for a 16.5-km reach of the Rambla de Cervera, a Mediterranean ephemeral stream located in eastern Spain. Channel changes were analysed through a range of techniques, specifically the analysis of aerial photographs with geographical information systems (GIS) and comparison of topographic surveys. The gravel channel underwent a general decline over the study period, losing width (68.5%) and surface area (45.7%) caused by the development of established islands frequently attached to the floodplain. These morphological changes exhibit an interesting temporal variability, with a maximum decrease of the gravel channel in the period 1946-1956 and another narrowing stage between 1977 and 1991. Two periods (1956-1977 and 1991-2006) also had mixed performance. In addition, incision processes occurred along the entire study reach at an average depth of 3.5 m. Natural and human-induced factors producing contradictory effects are considered responsible for changes in the Rambla de Cervera.