One of the most often-used parameters that describes morphology and runoff from a watershed is the time of concentration (Tc

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<p><strong> </strong></p> <p><strong>Gergely Ámon<sup>1</sup>, </strong>and Katalin Bene<sup>2</sup><strong> </strong></p> <p><strong> </strong></p> <p><sup>1,2</sup>National Laboratory for Water Science and Water Security, Széchenyi István University, Department of Transport Infrastructure and Water Resources Engineering, Egyetem square 1., H-9026 Győr, Hungary</p> <p> </p> <p>Flash floods and low-flow events often severely impact small, steep watersheds. Water resources engineers need to understand and prepare for these events. On small, steep-sloped watersheds, meteorological and watershed characteristics influence the behaviour of the overland flow. In this research, we applied different precipitation events in time and intensity</p> <p> on the watershed to determine the impact on outflow characteristics.</p> <p>The Hidegvíz-valley watershed on the north-western side of Hungary, a well-measured and instrumented experimental watershed, was selected for surface flow modelling. A 2D hydrodynamical model was developed and calibrated on a measured rainfall-runoff time series. Two measured rainfall events and triangular design rainfalls with different return periods were applied to the calibrated model to determine the impact on surface runoff attributes. Peak outflow, runoff ratio and runoff volume were selected to describe outflow characteristics. The results show that the peak flow at one rainfall event is much greater than at the other rainfall events. The volume of a rainfall event increases for longer-duration events. After certain rainfall events, the runoff ratio and runoff volume did not change much.</p> <p>The research will help to better understand runoff processes due to different rainfall events and durations and help to improve the design approach for flood and drought protection.</p> <p>Keywords: numerical modelling, hydrodynamics, overland flow, watershed model</p> <p> </p> <p>The research is carried out within the framework of the Széchenyi Plan Plus program with the support of the RRF 2.3.1 21 2022. 00008 project. </p>

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The common feature of streams in steep sloping watersheds is that there is a significant change from base-flow to flash-flood; sometimes two or three orders of magnitude. In Hungary, these streams are usually ungauged, with lack of available data, and models. The watershed features both urban and natural land use conditions, but the main area is quite homogenic.This paper evaluates the impact of different model parameterizations, and rainfall duration on flash-flood events in the Morgó-creek watershed. The goal is to find the main parameters that can represent the uncertainty of a flash-flood sensitive area, and how the calibrated and determined parameters take effect on a model if these values are shifted on given intervals.