How Safe is Hydrologic Infrastructure Design? Analysis of Factors Affecting Extreme Flood Estimation: Fid-Bau Portal

How Safe is Hydrologic Infrastructure Design? Analysis of Factors Affecting Extreme Flood Estimation

Sordo-Ward, Álvaro / Bianucci, Paola / Garrote, Luis / Granados, Alfredo

This study evaluates the implicit safety level in hydrologic infrastructure design, performed in common practice with the calculation of the peak-flow frequency curve for high return periods ( $100 < return period < 10,000 years$ ) through use of single-peak hyetographs in a semidistributed hydro-meteorological event-based model. Through consideration of two basins located in mainland Spain, the paper studies the effect on the peak-flow frequency curve of (1) the shape of the design hyetograph defined by the alternating blocks (AB) method or through applying a Monte Carlo (MC) procedure; (2) the catchment area (ranging from 140 to $1,800 {km}^{2}$ ); and (3) the extent of disaggregation in the hydro-meteorological model (varying from 14 to 66 subbasins). The effect on hydrologic safety was measured through using the ratio $R = QmaxAB / QmaxMC$ , with QmaxAB, the peak flows obtained with the AB method and QmaxMC, the application of MC. The paper finds the following: (1) that the degree of safety decreases as the basin area increases, regardless of the extent of disaggregation in the model used; (2) a greater disaggregation in semidistributed hydrologic models leads to greater water safety, mainly for smaller basins (in this study, $150 {km}^{2}$ ); and (3) at the level of subbasin, the degree of safety decreases as the time of concentration and area increase.