DERIVATION OF FLOOD HYDROGRAPHS IN UNGAUGED BASINS

Abstract

Estimation of floods is of extreme importance in designing hydraulic structures and systems, as well as in flood management, including ecosystem recovery. Accurate derivation of flood hydrographs in ungauged basins has additional challenges. The aim of this paper is to estimate flood hydrographs with different return periods using a semidistributed hydrological model, in the ungauged River basin of Benca, Albania. Benca River is part of Vjosa River, which is considered the last wild river of Europe. A frequency analysis of annual maximum daily precipitation is conducted for all meteorological stations in the study area. Average precipitation depths are calculated by constructing Thiessen polygons. Storm hyetographs distributions are determined using regional information. For precipitation abstraction, the Curve Number method is applied. Spatial distribution of runoff curve numbers is computed through GIS analysis, based on average antecedent moisture conditions, and hydrological soil-cover complexes. The watershed is modelled via HEC-HMS software, schematized into subbasins, and reaches. For generating hydrographs in each subbasin, the synthetic unit hydrograph recommended by the Natural Resources Conservation Service is used. The stream channel routing methodology applied is the Muskingum method. Subsurface components are also defined. Model results include floods with different return periods, their hourly flow rates, respective volumes, peak discharges, shapes, thus giving a complete representation of flood magnitudes the basin. The findings are relevant to policymakers, researchers, and engineers in the region.