Estimating flash flood discharge in an ungauged mountain catchment with 2D hydraulic models and dendrogeomorphic palaeostage indicators

摘要

There is still wide uncertainty about past flash-flood processes in mountain regions owing to the lack of systematic databasesnon former events. This paper presents a methodology to reconstruct peak discharge of flash floods and illustrates a case innan ungauged catchment in the Spanish Central System. The use of dendrogeomorphic evidence (i.e. scars on trees) togethernwith the combined use of a two-dimensional (2D) numerical hydraulic model and a terrestrial laser scan (TLS) has allowednestimation of peak discharge of a recent flash flood. The size and height distribution of scars observed in the field havenbeen used to define three hypothetical scenarios (Smin or minimum scenario; Smed or medium scenario; and Smax or maximumnscenario), thus illustrating the uncertainty involved in peak-discharge estimation of flash floods in ungauged torrents.nAll scars analysed with dendrogeomorphic techniques stem from a large flash flood which took place on 17 December 1997.nOn the basis of the scenarios, peak discharge is estimated to 79 š 14 m3 su00011. The average deviation obtained between floodnstage and expected scar height was u00010D09 š 0D53 m. From the data, it becomes obvious that the geomorphic position of treesnis the main factor controlling deviation rate. In this sense, scars with minimum deviation were located on trees growing innexposed locations, especially on unruffled bedrock where the model predicts higher specific kinetic energy. The approach usednin this study demonstrates the potential of tree-ring analysis in palaeohydrology and for flood-risk assessment in catchmentsnwith vulnerable goods and infrastructure.