Historical flash floods retromodelling in the Ondara River in Tàrrega (NE Iberian Peninsula)

Flash floods in the Ondara River have caused many fatalities and damages in the town of Tàrrega in the last 400 yr. Unfortunately, no flow records are available. However, floods can sometimes be reconstructed thanks to available historical information: limnimarks, written accounts and archaeological surveys. Indeed, from these data and using the retromodelling method on three different scenarios to take into account morphology changes, the peak flows of the seven greatest floods occurred in Tàrrega since the 17th century were estimated. The results showed that the heaviest flood's specific peak flow (10.7 m3 s 1 km 2) ranks among the highest ever modelled or measured in similar-sized catchments in the Western Mediterranean region. The results pointed out, as well, that the changes in channel's morphology (mainly, the disappearance of a mediaeval bridge under sediment) caused by one of the floods increased the hydraulic capacity of a crucial cross-section. All this resulted in modest floods invading the town less often, but with much faster and, thus, more destructive flows. A preliminary estimation of the results' uncertainty was 4% for great floods and 18% for modest floods. The reconstructed peak flows will be introduced in a database for a future use in climatic and hydrological studies.