Hydrogeomorphic Impacts of Floods in a First-Order Catchment: Integrated Approach Based on Dendrogeomorphic Palaeostage Indicators, 2D Hydraulic Modelling and Sedimentological Parameters

Floods represent frequent hazards in both low- and first-order catchments; however, to date, the investigation of peak flow discharges in the latter catchments has been omitted due to the absence of gauging stations. The quantification of flood parameters in a first-order catchment (1.8 km2) was realised in the moderate relief of NE Czechia, where the last flash flood event in 2014 caused considerable damage to the infrastructure. We used an integrated approach that included the dendrogeomorphic reconstruction of past flood activity, hydraulic modelling of the 2014 flash flood parameters using a two-dimensional IBER model, and evaluation of the channel stability using sedimentological parameters. Based on 115 flood scars, we identified 13 flood events during the period of 1955 to 2018, with the strongest signals recorded in 2014, 2009 and 1977. The modelled peak flow discharge of the last 2014 flood was equal to 4.5 m3·s−1 (RMSE = 0.32 m) using 26 scars as palaeostage indicators. The excess critical unit stream power was observed at only 24.2% of the reaches, representing predominantly bedrock and fine sediments. Despite local damage during the last flood, our results suggest relatively stable geomorphic conditions and gradual development of stream channels under discharges similar to that in 2014.